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VR14/VR17 CRT display monitor user's manual

1. 2 2 INTERNAL CONTROLS ceroma al ae Al ite wee ee 2 2 INPUT SIGNAL REQUIREMENTS 2 2 THEORY OF OPERATION X AND Y DEFLECTION CIRCUITS 3 1 PLUS AND MINUS LOW VOLTAGE REGULATED SUPPLY 3 5 CRT ELECTRODE VOLTAGES 3 6 HIGH VOLTAGE POWER SUPPLY 3 6 W682 AND W684 INTENSITY CIRCUITS 3 10 LIGHT PEN AMPLIFICATION 3 13 375 Light ben Sua s IE Se Ge 3 14 MAINTENANCE PREVENTIVE MAINTENANCE 4 1 TROUBLESHOOTING rn ass kusanmi ek nt e 5 4 1 Picture ee aa Sara ee Gh ae eae 4 1 Pauly Picture a a a ee ee lee 4 5 ASSEMBLY REPLACEMENT INSTRUCTIONS 4 5 Deflection Heat Sink Removal 4 5 7007165 Power Regulator Assembly Removal 4 7 Regulator Heat Sink Removal 4 9 Yoke amb CRT Removal o oe wa ass s RS c eoo ges ORC A M UN 4 9 High Voltage Supply Removal 4 11 ENGINEERING DRAWINGS POWER SUPPLY TROUBLESHOOTING DEFLECTION AMPLIFIER TROUBLESHOOTING A225 REPAIR iii Figure No 1 1 1 2 2 1 2 2 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 4 1 4 2 4 3 4 4
2. o i NE Z SELECT L R3 100 RIO IOO K Z DIRECT INPUT D UNLESS OTHERWISE INDICATED DIODES ARE 0664 CAPACITORS ARE 100 20 El IS DEC7400N PIN 7 ON IC GND PIN I4 5V RESISTORS ARE 1 4W 10 NOTE This schematic may not reflect most recent engineering changes Figure 3 3 D6 6 gt TO CHANNEL SELECT SWITCH El O M F TO GRID 1 E TO BRIGHTNESS POT SLIDER Intensity Amplifier W682 Circuit Schematic DI3 05 D662 D662 RI2 330 U OUT D7 DEM 014 IN3039B CP 0764 CATHODE PULSE GENERATOR Z INPUT LOW VOLTAGE DETECTION 5 80V INTOL INTENSITY LEVEL GENERATOR INT L INT 2 L NOTE1 One of eight intensity levels as determined by the three intensity inputs NOTE 2 Brightness determined by grid 1 voltage which is a function of the intensity level generated and BRIGHTNESS pot position 80V CATHODE GRID LEVEL 222 GENERATOR BRIGHTNESS FRONT PANEL CP 076l Figure 34 W684 Intensity Control 3 5 W682 AND W684 INTENSITY CIRCUITS In the VR14 without the light pen option the intensifi cation of points on the screen is controlled by the W682 circuit board The intensity signal is routed to pin J This signal is a transition from a high to a low While the Z signal is at a high above 2 4 V the output from gate A pins 8 9 10 is low When the Z input is low momentarily the output of A goes high This posi
3. P2 P2 P2 gt N N NN gt YN CN m Indicates voltage depends upon input signal Table 4 1 VR14 VR17 Voltage Check Points Voltage 2 2V nominal 2 2V nominal 22 Vdc Red 22 Vdc Blue 5 Vdc 21 Vdc 22 Vdc 21 Vdc 22 Vdc 43 Vdc Orange 42 Vdc Gray Yellow 22 Vdc Red 43 Vdc Green 42 Vdc Gray Blue 22 Vdc Blue 43 Vdc Ground 43 Vdc 3 5 Vrms Ground 3 5 Vrms 70 Vrms 200 P P 150 Vrms 400 P P 22 Vdc Red Ground Black 22 Vdc Red 0 Vdc Black 80 to 400 Vdc Gray Red 400 Vdc Orange Signal Control X Current Sample Y Current Sample X Input Signal Y Input Signal Regulated dc Regulated dc For W682 W684 Component PNP Base 2N4399 PNP Emitter 2N4399 All Collectors NPN Base 2N5302 NPN Emitter 2N5302 Component Emitters of 2N4399 Bases of 2N4399 Collectors of 2N4399 Emitters of 2N5302 Bases of 2N5302 Collectors of 2N5302 Signal Control Raw dc Raw dc 1 2 Filament 1 2 Filament 80V tap 400V tap Regulated Hot Sense Cold Sense Focus Grid 2 Table 4 1 Cont VR14 VR17 Voltage Check Points 7007165 G836 Regulator Circuit Connectors P1 P2 P4 Voltage Signal Control 3 5 Vrms Brown Filament P4 8 3 5 Vrms Brown Filament P4 9 80 Vdc Gray Green To Brightness Potentiometer P4 10 0 to 40 Vdc Gray Violet Brightness
4. 1 3 BLOCK DIAGRAM DESCRIPTION Figure 1 1 is the functional block diagram of the VR14 without the light pen option The X and Y position signals are connected to their respective A225 Deflection Ampli fier Circuit Boards The A225s boost the input signal to a level sufficient to drive the power transistors while also providing gain and position controls In turn the power transistors drive the deflection yoke that positions the electron beam on the screen The yoke currents are then passed through a 0 5 resistor that converts the yoke currents back into voltages that are used as feedback for each A225 deflection amplifier This feedback allows the A225 to produce an exact current replica in the yoke of the input signals The intensity input is applied to the W682 circuit board that converts this input to a 60 V pulse which drives the cathode The cathode pulse is negative going this pulse turns on the electron beam creating a spot on the screen The W682 accepts a gating input that allows the intensity pulse to be time multiplexed between two input sources The G838 Fault Protection Board disables the intensity circuit in the event of a 22 V failure This prevents the phosphor screen from burning as there would be no deflection under these conditions Line power is passed through a fuse an on off switch and then through one normally closed thermal cutout switch The switch is located on the 22 V regulator heat sink and in the
5. Also at least a 500 ns waiting period must be allowed to intensify a dot before commanding the electron beam to move to its next location Not giving enough time to intensify a dot after the deflection is settled will also smear the dot since the deflection amplifier will start drag ging the dot to the new position The amount of delay required from the time new X and Y position information is presented to the VR14 VR17 and the intensify pulse is requested depends upon how large a position change is requested and how perfectly settled the dot has to be to its final ideal position Full scale deflection changes such as far left to far right or corner to corner require a 20 us waiting period for the dot to settle to within 0 01 inch of its final value If larger errors can be tolerated 18 us may be used Small deflec tion changes require much less time A 0 1 inch change can be settled in less than 1 us If there is no way for the circuits driving the VR14 VR17 to distinguish small position changes from large ones each change must be assumed to be large and thus requires the worst case delay Also if the D A converters driving the display have gliches error spikes generated while changing values proportion ately longer delays are required since the deflection amplifiers have to recover from the gliches The Z direct input applicable only to VR14s without light pen option allows direct modulation of the bright
6. dangerous but the surprise may cause the user to drop the CRT Never hold the CRT by the neck the thin cylindrical portion alone since it will break off Remove the 7007165 as shown in Figure 44 and unscrew the four 6 32 heat sink mounting screws from the side chassis Remove two pin connector from the high voltage bracket aam CTA b Lift heat sink straight out and repair faulty transistor NOTE Thermal cutouts have line voltage on them be sure line cord is removed Figure 4 5 Regulator Heat Sink Removal 4 10 The VR14 has a shell bond frame by which it is directly fastened The VR17 CRT is fastened to its support bracket by four clamp tubes DEC part no 7411301 mounted to the CRT by a worm gear clamp DEC part no 9009555 The clamp tubes and worm gear clamp are reused when replacing the VR17 CRT When installing a new CRT on the VR17 mount the 4 clamp tubes to the CRT using the worm gear clamp Do not tighten fully but leave sufficient slack so that the clamp tubes may be aligned with the support bracket screw holes Once the clamp tubes are aligned and the CRT fastened to the support bracket tighten the worm gear clamp 4 3 5 High Voltage Supply Removal To remove the high voltage supply proceed as follows 1 Remove the yoke and CRT as outlined in Paragraph 4 3 4 Ensure that the line cord is unplugged Disconnect the two red and two white wires from the high voltage
7. peak to peak and 1 7 V for Y when Ri and R2 on the A225 3 3 Figure 3 1 For larger input signals R1 and R2 are normally 10 With 10 the maximum input sensitivity is 0 5 V inch The input impedance is 5 kQ minimum for maximum sensitivity R1 and R2 3 3 POSITION GAIN HORIZONTAL VERTICAL BRIGHTNESS PRESET FOCUS 5481 1 Figure 2 2 Locations of Internal Controls and 20 minimum for Ri and R2 10 When driving long cables more than 30 feet high speed deflection may not be possible unless the cables are terminated in a low impedance less than 100 Q since the VR14 VR17 input impedance is too high for this application Input signals larger than 2 V may be used by attenuating with the gain controls and R1 and R2 on the X and Y deflection circuit boards However the potentiometers become much too sensitive for input signals greater than 10 V peak to peak and R1 and R2 should be increased to provide pre attenuation for these larger input signals The input signals may be bipolar such as 5 V or unipolar such as 0 V to 5 V or 0 V to 5 V The position potentiometer allows the deflection to be offset plus or minus half a screen thus a unipolar signal may be completely centered on the screen Offsets more than half of the full scale inputs cannot be handled In other words if the full scale deflection is offset from 0 V by more than half its full scale value centering on the
8. which through R9 adds or subtracts voltage from the actual input signal This allows the displayed information to move up down left right on the screen or in the case of offset input signals allows the information to be centered on the screen SIGNAL 150pF TYPICAL R31 R10 YOKE 2 2 IK RETURN R30 NOT p 270 USED C13 R7 4 64 1 8W 1 INPUT PWR Y GND Ll SIGNAL H GND R25 1 2W Q3 R26 10 1 2W UNLESS OTHERWISE INDICATED ALL CAPACITORS ARE 10pF 1004 5 22V ALL DIODES ARE 0664 22v 0 0 JUMPERS FOR THE A 225 YA VARIATION Ri amp R2 ARE 3 3K 1 4W 5 FOR INPUT SIGNALS LESS THAN 5V P P NOTE This schematic may not reflect most recent engineering changes ss YOKE ASSY y 7007088 r TOPINA YOKE RETURN 0 5 25W 1 TO PIN H SIGNAL GND 0762 Figure 3 1 X and Y Deflection Circuit 3 3 The remaining component the 225 is frequency compensation which allows the amplifier to operate over its required bandwidth without oscillation Because the ampli fier must operate from dc to beyond 1 MHz the voltage gain must be reduced continuously at higher and higher frequencies If this were not done excessive phase shift between input and output from feedback could cause the output to be in phase with the input and thus oscillate R12 R3 R32 C16 C15 and C11 perform the required gain reduction functions R12 reduces the
9. PL 7007078 0 0 Top Mtg Assy D AD 7007077 0 0 Top Mtg Assy PL A PL 7007077 0 0 CRT Yoke Assy D IA 7007088 0 0 Light Pen Assy C UA 375 0 0 VR14 Accessory List A AL VR14 0 7 CHAPTER 5 ENGINEERING DRAWINGS Table 5 2 Engineering Drawings Drawing No Drawing Directory B DD VR17 0 Engineering Specification A SP VR1 704 Block Schematic D IC VR14 0 1 Module Utilization C MU VR14 0 3 Module Utilization A PL VR14 0 3 Circuit Schematic G836 D CS G836 0 1 Circuit Schematic G840 D CS G840 0 1 Circuit Schematic A225 D CS A225 0 1 Circuit Schematic W684 D CS W684 0 1 Cable Keybd Interlock C IA 7009248 0 0 Circuit Schematic Heat Sink Circuit Schematic Deflection Circuit Schematic Power Supply VR17 Display Assy VR17 Display Assy PL Wired Assy Wired Assy PL Top Mtg Assy Top Mtg Assy PL CRT Yoke Assy Light Pen Assy VR17 Accessory List C CS 7007080 0 1 C CS 7007082 0 1 D CS 7007084 0 1 D UA VR17 0 0 A PL VR17 0 0 D AD 7007078 0 0 A PL 7007078 0 0 D AD 7007077 0 0 A PL 7007077 0 0 D IA 7007088 0 0 C UA 375 0 0 A AL VR17 06 The power regulator heat sink contains a thermal cutout connected to the input line voltage Always remove the line cord before handling the heat sink Generally if the 22 V reads above 25 V one or both of the regulator transistors has shorted The 22 V is con trolled by the PNPs 2N4399 that are the front set of transistors on the regulator heat sink a
10. Preset P4 11 80 Vdc Gray Orange For W682 W684 P4 12 22 Vdc Blue Hot Sense 4 13 O Vdc Black Cold Sense P4 15 22 Vdc Blue Regulated Note All voltages measured with respect to ground chassis or 02 Pi 2 8 5 9 6 HIGH VOLTAGE POWER SUPPLY 7007165 BRIGHTNESS FOCUS ADJ 6836 W CONNECTORS PRESET ADJ 6582 5 Figure 4 1 VR14 VR17 Interior View With an oscilloscope or meter measure 2 2 V maximum at AQ2 A with respect to ground 02 This point 02 is the X axis deflection coil current sample Because coil current flows through a 0 5 Q resistor voltage measured at 02 multiplied by two equals the current flowing With the A225 circuit cards removed no coil current should flow Momentarily tum on power to the VR14 VR17 If 02 has any voltage plus or minus refer to Appendix B a deflection power transistor probably is shorted Measure the same as in step 5 for the Y axis deflection coil current at A03 A with respect to ground A02 V Momentarily tum VR14 VR17 power on and off No voltage should be read this indicates no Y deflection coil current is flowing If any voltage is observed refer to Appendix B since a Y axis deflection transistor is probably shorted Replace the G838 G840 circuit into 01 and the A225 circuit into 02 Still leave the Y axis A03 board out Measure less than 2 2 V at pin 2 with respect to ground A02 V Momentarily
11. SUPPLY The high voltage supply is a self contained high voltage source that requires only line voltage input The input is actually the split primary of its own internal step up transformer For 115 V operation the primary windings are operated in parallel for 230 V operation they are operated in series The step up transformer delivers high voltage ac to a voltage doubler and filter The ultimate dc voltage is 10 5 kV and unregulated Thus the high voltage is slaved to the line voltage and varies linearity with it Because the electron beam is accelerated by the high voltage the ability to deflect the beam will change as the high voltage changes If a constant deflection current flows through the yoke the amount of deflection is reduced if the anode high voltage is increased smaller displayed picture the deflection grows if the anode high voltage decreases larger displayed picture The actual deflection factor change is proportional to the square root of the ratio of the old anode voltage to the new anode voltage 1 deflection factor IVa For example if the high voltage is halved the deflection would grow 1 414 V2 1 In terms of line voltage the deflection factor is approxi mately 0 4 of the change i e a 5 percent line change causes a 2 percent deflection change The VR14 VR17 incorporates circuitry which protects the unit from possible damage due to arcing Arcing is due to transient conditions within the CRT
12. X 228 6 mm 210 X 280 mm VR14 and VR17 Spot Size lt 20 mils inside the usable screen area at a brightness of 30 fL Jitter lt 1 2 spot diameter Repeatability lt 1 spot diameter Repeatability is the deviation from the nominal loca tion of any given spot Gain Change From a fixed point on the screen less than 0 3 gain change for each 1 line voltage variation Temperature Range 0 to 50 C operating Relative Humidity 10 to 90 noncondensing Brightness gt 30 fL for VR14 gt 25 fL for VR17 measured using a shrinking raster technique Linearity Maximum deviation of any straight line is lt 1 of the line length measured perpendicular to a best fit straight line Deflection Method Magnetic 70 diagonal deflection angle Focus Method Electrostatic High Voltage 10 5 dc nominal voltage proportional to input line voltage Supply is self contained and equipped with a bleeder resistor Shielding CRT is fully enclosed in a magnetic shield Overload Protection Unit is protected against fan failure or air blockage by thermal cutouts Power supply and amplifiers are current limited Phosphor protection is provided against fault conditions Deflection Amplifier a Deflection amplifiers are dc coupled and are capable of sustaining a full screen ac or dc deflection at environmental extremes b Input Specifications 1 Inputs are differential 2 Differential input imp
13. as described above and double check that the line cord is removed With a long bladed screwdriver that is grounded to the chassis a clip lead between the screw driver blade and chassis plus a second clip lead for safety is adequate slide the blade under the rubber cup on the high voltage connection at the CRT and touch the anode connection to discharge any remaining high voltage At the same time remove the high voltage connection The connection is made by two stiff wires that each have a bend or hook on the end The connection at the CRT is made by squeezing these two wires together so they can fit in the CRT metallic hole Then those two wires are let go so they can expand and grab the inner lip of the CRT with the hooked ends The connection is removed by squeezing the hook wires together and at the same time pulling them out so that the wires can clear the anode hole Remove the CRT plastic mask by removing the top and bottom screws from the front bezel casting The CRT is held by four screws one at each corner of the screen As each screw is removed support the weight of the CRT CAUTION The CRT is under high vacuum and is potentially in danger of implosion if subjected to sharp blows or very rough handling Also to avoid dropping the CRT accidentally never place your hand over the anode high voltage button while picking up or carrying the CRT in case the CRT has residual charge The shock is not in itself
14. event of a fan failure or excessive temperature on the heat sink VR14 VR17 input power will be shut off until it cools down The line power is then connected to the power transformer the high voltage power supply and the fans The high voltage supply converts the input line voltage to 10 5 kV that is connected to the CRT anode The power transformer has three basic secondaries a 6 3 V for fila ment a 70 150 for CRT electrodes and a 72 V center tapped for deflection The 72 Vac is rectified and filtered to provide 43 Vdc unregulated This 43 Vdc is regulated with circuits on the G836 board along with four power transistors on the regulator heat sink assembly The regulated output is 22 Vdc and is distributed to the deflection amplifiers The 70 150 ac is rectified and filtered on the G836 to generate 80 Vdc and 400 Vdc The 80 Vdc is used for the brightness potentiometer which is tied to the grid One side of the brightness control is connected to another potentiometer on the G836 which can adjust the maximum brightness range of the brightness potentiometer The 400 Vdc is supplied directly to grid 2 and also to one side of the focus potentiometer on the G836 board The wiper of the focus potentiometer goes directly to the focus electrode on the CRT Figure 1 2 is a block diagram of the VR14L and VRI7L i e VR14 VR17 with the light pen option Note that the G840 Light Pen Amplifier replaces 6838 Fault Protec tion Circuit B
15. is held at a TTL low Thus if two separate pieces of information are to be displayed by placing Z select at a high only during Channel 1 intensification times and low only during Channel 2 intensification times both curves will be displayed when the channel select switch is at 1 amp 2 and only Channel 1 when Channel 1 is selected and Channel 2 when Channel 2 is selected In the VR14L and VR17L brightness level is a function of three input signals Intensity 2 0 as well as the front panel brightness control These input signals combine in the W684 module to generate a voltage which is applied to grid 1 of the CRT establishing a particular brightness level 3 1 X AND Y DEFLECTION CIRCUITS The X and Y deflection circuits are identical therefore only one axis will be described The deflection circuit consists of the A225 circuit board two power transistors and a deflection yoke Figure 3 1 The input signal is applied to pins E and B on the A225 circuit board The input signal is handled as a differential or balanced signal even if the input is driven from a single ended source the single ended source being a special case of a balanced input where one side is grounded Ri and R2 establish the minimum input impedance and form an attenuator with R3 the gain potentiometer The voltage developed across R3 is amplified and converted from balanced to single ended by amplifier El El is an inverting amplifier whose gain is estab
16. open loop gain of E2 at all frequencies C11 reduces the gain of Q2 at high frequencies and is of major significance to the overall bandwidth The yoke itself represents a major roll off for the amplifier and its high frequency characteristics domi nate the stability of the amplifier An RC network across the yoke enhances the high frequency settling character istics of the yoke The power output stage 2N5302 and 2N4399 is current limited by the 22 V and 22 V power supply regulators If the deflection amplifiers are driven way off screen the power supply limits the maximum current to 11 A If this condition is allowed to exist eventually either the 22 V fuse or the 22 V fuse will blow rendering the circuit safe from such overloads 3 2 PLUS AND MINUS LOW VOLTAGE REGULATED SUPPLY The input line voltage is stepped down in the power transformer to approximately 36 Vrms There are two identical secondary windings to deliver these 36 V Both windings are connected in series making a 72 V center tapped winding Using full wave bridge rectification the ac becomes approximately 86 Vdc By grounding the center tap the 86 Vdc split evenly with respect to ground thus a 43 V and a 43 V are available with respect to ground A filter capacitor on each 43 V line smooths the ripple and finishes the task of generating the raw unregulated dc for the 22 V regulators The regulators are contained on the G836 circuit board Figure 3 2 and
17. pin D In the event of a failure of either the 22 V supplies deflection ceases and a bright spot could occur on the CRT causing a burn To prevent this G838 Figure 3 5 contains a circuit that supplies 5 V to the W682 If either the 22 V or 22 V goes to O in the case of a short circuit or blown secondary fuse the circuit supplying the 5 V shuts down Because the G838 has a low value resistor across the 5 V 47 Q the 5 V line pin A on the W682 is grounded 3 11 This causes the base drive to Q1 to be shunted to ground through D16 and renders Q1 off this shuts off the CRT UNLESS OTHERWISE INDICATED RESISTORS 1 4 5 0757 Figure 3 5 6838 Circuit Diagram In the VR14L and VR17L the intensification of points on the screen is controlled by the W684 module The Z input intensity signal enters the W684 at pin J drawing D CS W684 0 1 Before the Z input is asserted pin J is a TTL high The output of E2 pin 3 is low disabling the two AND gates E2 pin 6 and E2 pin 11 This causes Q7 to be cut off and Q6 to conduct Consequently Q2 is cut off because its base is low at this time With Q2 cut off the cathode voltage at pin U will be positive approximately 62 V and no beam is generated The cathode voltage is produced by the Zener action of D4 from 80 V input from the G836 When the Z input is asserted E2 pin 3 is disabled and E2 pin 6 and E2 pin 11 are enabled Now the situation is reversed is cu
18. position signal E2 compares the input voltage at R11 with the feedback voltage at R31 R10 Because the amplifier has voltage gain only a small voltage is needed between pins 10 and 9 of E2 to cause large changes in the output Pin 9 of E2 is referenced to ground through R13 which is strictly an impedance balancing resistor that minimizes offsets in E2 due to temperature changes Therefore pin 9 is essentially grounded If any voltage appears at pin 10 of E2 the output will immediate ly respond in a manner that tends to reduce the voltage at pin 10 to zero thus a null is always achieved at pin 10 of E2 If a variable voltage is present at the input of R11 the output or yoke current will vary in such a manner that a continuous null is achieved at pin 10 The only way this can occur is if instantaneously the yoke current undergoes exact equal and opposite changes to those occurring at the input to R11 Therefore the yoke current will be an exact but opposite polarity replica of the input voltage In absolute numbers the actual yoke current versus input voltage can be determined by comparing resistor ratios For example if 1 V is applied to the input of R11 1 mA will flow through R11 This occurs because the amplifier forces pin 10 of E2 to 0 V thus one side of R11 is O V the other is 1 V so 1 mA flows This current does not flow into pin 10 of E2 because if it did pin 10 would rise in voltage because the input of E2 looks lik
19. the 43 V to drop the null would again be disturbed and El would act in a way that would turn on the output hard enough to return to its proper level the level that maintains the null This regulating action takes place in a matter of micro seconds The actual output voltage at which the null will be maintained is determined by the ratio of R3 to R2 times the reference voltage The mechanics of how EI controls the output can be traced stage by stage El drives emitter follower 1 to give the output of El sufficient drive capability to fully turn on Q2 if required Q2 through R12 controls the base current of the series pass transistors that are external to the G836 board The pass transistors maintain a constant output since they are supplied power from the raw dc source Because of the high open loop voltage gain high frequency networks are used to roll off the gain of the regulator to ensure stable nonoscillatory operation C2 R5 and C5 serve this purpose The output power transistors are current limited by D13 and D14 These diodes conduct whenever excessive collec tor current is demanded In so doing the diodes limit the base drive thereby limiting the maximum fault current that may flow 3 3 CRT ELECTRODE VOLTAGES The CRT requires the following electrode voltages fila ment cathode grid 1 grid 2 focus and anode The filament voltage is derived from the 3 5 Vac windings of the power transformer The 3 5 Vac
20. windings are connected in series yielding 7 Vac Due to resistance losses approximately 6 3 Vac is provided across the CRT filament The 70 Vrms winding is used to provide cathode and grid 1 bias voltages The 70 Vrms winding terminates on the G836 Figure 3 2 Through Dil C17 R36 and C16 this winding generates a 80 Vdc by half wave rectification The same winding in like manner generates 80 Vdc from D12 C18 R37 and C19 The 80 V is applied to one side of the front panel brightness potentiometer The other side of the potentiometer returns to the brightness preset potenti ometer G836 R38 R38 setting determines the maximum voltage that can be made available to grid 1 and thereby acts as a limiter of the maximum intensity The wiper of the brightness potentiometer is connected to pin E of the W682 W684 circuit board In VR14 versions where the W682 Intensity Control Figure 3 3 is used pin E connects by way of R9 to grid 1 of the CRT The W684 Intensity Control is used in the VR14L and VRI7L In the W684 Figure 34 and drawing D CS W684 0 1 the voltage at pin E is modulated by the three intensity signals Intensity 2 0 before it is sent to grid 1 Operation of W682 W684 circuitry is explained in Paragraph 3 5 The bias voltage applied to grid 1 of the CRT may vary from 80 Vdc to 0 V the upper limit being determined by the setting of R38 on 6836 Intensity on the screen is generated by cathode pulses from t
21. 0 V and is 100 V The VR14 VR17 can operate with any of the three input line voltages simply by changing the jumpers and interconnections on TB1 and TB2 Figure 2 1 and drawing D CS 7007084 0 1 Equipment cooling is the most important VR14 VR17 installation requirement Fans draw air from the bottom of the unit therefore at least 1 inch of free air space must be provided below the bottom chassis The table top model keeps the bottom 1 inch above the table surface In the rack mounted unit if equipment is mounted immediately below the VR14 as long as there is open area under the VR14 fans a screen is acceptable a solid plate closer than linch is not proper cooling can occur The same requirements apply on the rack mounted unit to the area immediately above the unit The table top model has a solid top cover The cooling air exits from the rear of the unit Therefore at least 2 inches of free space must be provided immediately behind the unit Do not push the VR14 VR17 flush against a wall or solid vertical surface that would cut off air circulation NOTE Before applying power to the VR14 VR17 ensure that the position potentiometers are set for the particular input signals being used Because of the universal nature of allowable input signals the deflection amplifiers may be driven into saturation far off screen by position settings Leaving the deflection amplifiers satu rated way off screen continuously may cause dama
22. 4 5 Table No 1 1 2 1 2 2 2 3 3 1 4 1 5 1 5 2 ILLUSTRATIONS Title Page Block Diagram of VR14 Without Light Pen Option 1 4 VRIAL VRI7L Block Diagram 1 5 Input Power Jimiper as v ie br ERR ACE Ke RCRUM 2 1 Locations of Internal Controls 2 6 X and Y Deflection Circuit 3 3 G836 Circuit Board Part of the 7007165 Power Regulator Assembly 3 7 Intensity Amplifier W682 Circuit Schematic 3 9 W684 Intensity Control 3 10 839 Circum Di gram gt Swan ee RER Te CA 3 11 VR14L VR17L Brightness and Contrast Control 3 12 Light Pen Amplifier scema Wr AA RR 3 13 Light Pen Pulse Timing 6840 Module 3 14 VR14 VR17 Interior View 4 3 Deflection Heat Sink Removal 4 6 7007165 Power Regulator Assembly 4 7 7007165 REMOVAL ss e osa na rn ee De ea TTL 4 8 Regulator Heat Sink Removal 4 10 TABLES Title Page VR14 and VR17 Configurations 1 1 J17 Rear Connector Pin Assignments 2 3 118 Rear Connector Pin Assignments 2 5 Control Settings pter eg a e
23. 82 apply a proper Z input 3 V to 0 V transition at J17 pin 4 and check to see that the signal reaches A04 J If so check A04 R with the channel select in the 1 amp 2 position to see that a high is present there If so see that 5 V is being supplied to A04 A If A04 A is less than 4 V replace or repair the G838 module as this is where the 5 V is developed If the three preceding measurements are good and the W682 output measured at A04 U is not going from 60 V to for at least 300 ns repair or replace the W682 module To check the W684 apply 0 V ground to the Z input at J17 pin 4 and check to see that it reaches A04 J If so see that 5 V is being supplied to A04 A If 04 is less than 4 V replace or repair the G840 module as this is where the 5 is developed If the two preceding measurements are good and the W684 output measured at A04 U is not at approximately repair or replace the W684 module Measure 6 3 Vac between P4 7 and P4 8 and observe the glowing filament on the CRT No 6 3 Vac can be traced back to the power transformer by way of P2 pins 1 and 2 Measure the grid 1 voltage at A04 F It should vary from 80 Vdc to between 30 V and 0 V when the front panel brightness control is varied The 80 Vdc comes from the G836 board Trace back to the G836 Measure grid 2 at P4 6 It should be at least 300 V Trace back to the G836 The last item operating improperly for pict
24. LIFIER POWER lt 20 ran PS 115 0 5 x VAC CURRENT SAMPLE Y FEEDBACK 0758 Figure 1 1 Block Diagram of VR14 Without Light Pen Option S I FROM THERMAL CUTOUT 115 INTENSITY INTENSITY 2 INTENSITY OUT 115 VAC FAN 115 22V PASS 22V PASS Ea THERMAL 115 RANSISTORS rRANSISTORS b CUTOUT UNIT POWER RECTIFIERS 22V FILTER CAP ae B 22 HIGH POWER SUPPLY amp Focus VOLTAGE 115VAC POWER A a REGULATOR BOARD POWER ila N E 6836 SUPPLY UE bate Ku ee ee ROM 1800 00 ANODE BRIGHTNESS FOCUS 6 3 PRESET Bea VAC en 61 62 5 DEFLECTION d 80V INTENSITY gt 4 80V LIGHT PEN INDUT X FEEDBACK 22V URRENT 22V BRIGHTNESS CONTRAST SAMPLE DEFLECTION LIGHT PEN X INPUT AMPLIFIER PULSE X INPUT A225 Y INPUT Y DEFLECTION Y INPUT AMPLIFIER A225 0 5 fv CURRENT SAMPLE Y FEEDBACK L CP 0760 Figure 1 2 VR14L VR17L Block Diagram 2 1 INSTALLATION The VR14 is shipped either as a standard RETMA 19 inch by 10 1 2 inch 10 7 16 inch rack mounted unit or as a table top model without chassis slides with its own decorator cover The VR17 comes only in a table top model The VR14 VR17 can operate from a power line frequency between 47 and 63 Hz The input line voltage however is specified by a letter designation after the VR14 VR17 is 115 V A D is 23
25. Prolonged off screen deflection of the CRT beam can damage the VR14 VR17 Ensure that the X and Y driving signals into the VR14 VR17 never drive the CRT beam off screen because of intermittent incorrect signals 4 2 TROUBLESHOOTING VR14 VR17 voltage checks Table 4 1 and most tests can be done with a volt ohm milliampere meter however an oscilloscope will be needed if waveform analysis is required NOTE When making voltage measurements on a malfunction VR14 VR17 set the voltmeter or oscilloscope to the proper range connect the leads to the test points then turn the power on and off very quickly so that the anticipated reading may be taken Power is only on for a very brief moment In this way fault condi tions may be discovered without causing further damage Never leave power on to a malfunctioning or repaired VR14 VR17 until all necessary checkpoints are measured and proved nominal CHAPTER 4 MAINTENANCE The circuit card connector block as viewed from the wiring side is labeled A01 and A04 left to right on the top section and B01 to B04 on the bottom section Figure 4 1 shows pin and connector locations for P1 P2 P3 and P4 4 2 1 No Picture Probably the most common failure mode with this type of equipment is no picture Unfortunately this condition can be caused by almost any malfunction such as a loss of input intensity pulse incorrect input deflection signals driving the beam off the screen a power suppl
26. VR14 VR17 CRT display monitor user s manual EK VR14 OP 005 VR14 VR17 CRT display monitor user s manual digital equipment corporation maynard massachusetts 1st Edition April 1971 2nd Printing Rev June 1971 3rd Printing Rev June 1972 4th Printing Rev January 1973 5th Printing July 1973 2nd Edition December 1973 7th Printing November 1974 Copyright 1971 1972 1973 1974 by Digital Equipment Corporation The material in this manual is for informational purposes and is subject to change without notice Digital Equipment Corporation assumes no respon sibility for any errors which may appear in this manual Printed in U S A The following are trademarks of Digital Equipment Corporation Maynard Massachusetts DEC PDP FLIP CHIP FOCAL DIGITAL COMPUTER LAB 1 1 1 1 2 1 3 2 2 1 2 2 2 3 2 4 2 5 3 3 1 32 3 3 3 4 3 5 3 6 3 6 1 CHAPTER 4 4 1 4 2 4 2 1 4 2 2 4 3 4 3 1 4 3 2 4 3 3 4 3 4 4 3 5 CHAPTER 5 APPENDIX A APPENDIX B APPENDIX C CONTENTS Page GENERAL INFORMATION INTRODUCTION er u A SLE E e Noe A A a 1 1 SPECIFICATIONS 555 sa Bre wa a QU o dt 6d 1 1 BLOCK DIAGRAM DESCRIPTION 1 3 OPERATION INSTALLATION By ie S 2 1 FRONT PANEL CONTROLS 595 3 Aro A Bee 2 1 REAR PANEL CONNECTORS
27. a polished cylinder approximately 0 45 X 5 0 inches The output signal connection is via a cable that plugs into the VR14L VR17L front panel When an intensified beam strikes the CRT phosphor where the light pen is being aimed the phototransistor Q1 conducts and negative going alternation is output to the G840 Light Pen Amplifier module Figure 3 7 In the G840 the light pen output is shaped to become the TTL compatible signal LIGHT PEN PULSEL d E TUI gt 8 7045 5 note 1 This output must be low before a second LIGHT PEN PULSE L signal can be asserted 0571 Figure 3 8 Light Pen Pulse Timing G840 Module This chapter deals with the prevention diagnosis and repair of fault conditions Successful troubleshooting of the VR14 VR17 can be performed using a volt ohm milliampere meter however an oscilloscope facilitates and expedites isolation and repair of faults 4 1 PREVENTIVE MAINTENANCE VR14 VR17 preventive maintenance consists of ensuring that the equipment is getting and maintaining proper air flow for cooling and a periodic cursory inspection for abnormal hardware conditions Because of the power dissipation on the deflection and regulator heat sinks good air flow must be maintained A periodic check is required to see that fans are operating properly and are not obstructed by dirt dust accumulation or inadvertently blocked by external equipment or surfaces
28. apply power If the voltage is within safe limits within 2 2 V leave power on and adjust the position potenti ometer on the A225 circuit Doing this should change the voltage reading on 02 providing the A225 indeed is controlling the coil current Return the position potentiometer to its origi nal position If the voltage at 2 is beyond 2 2 V shut down immediately Because the position potentiometer on the A225 can drive more current than the 2 2 V limit signifies 4 4 A it is possible that it the position potentiometer has been adjusted to one extreme or the other To prove whether this is the case or if the A225 circuit board is faulty turn the position potentiometer as fol lows clockwise if the voltage at 02 was very negative counterclockwise if the voltage at A02 A was very positive If no change is noted at 2 after adjusting the position potenti ometer the A225 board is faulty and should be replaced or repaired refer to Appendix Repeat the same tests as in step 7 for the Y axis deflection circuit A225 plugged into Monitor Refer to Appendix for A225 repair 4 4 10 11 12 13 If the fault has not been isolated the intensity circuit W682 W684 the electrode voltages and the high voltage supply are suspect The output of the W682 W684 drives the cathode At rest it should be 62 V and when triggered go to approximately 0 V To check the W6
29. de being the VR14 VR17 uses the deflection signal with respect to its own ground and not the VR14 VR17 ground which most likely is different and could cause picture ripple and hum If a separate ground is not available the single deflection signal is applied to one side of the differential input The remaining differential input is terminated with the source impedance of the driving signal or if this is low the input is simply grounded signal ground not chassis ground Signal ground is pin 9 and pin 12 X and Y signal ground deflection signal itself The Function For VR14 VR17 options GND For VR14 VR17 options 22 For VR14 VR17 options Bell Speaker Used with LK40 option KB Signal Used with LK40 option KB Signal Used with LK40 option Not Used 22 V GND Jumpered from J18 pin 1 to J18 pin 8 by P18 Jumpered from J18 pin 2 to J18 pin 9 by P18 Jumpered from J18 pin 3 to J18 pin 10 by P18 Provides 5 V to LK40 option Provides GND to LK40 option Provides 22 V to LK40 option respectively Never use chassis ground for X and Y input reference always use signal ground When using balanced or differential inputs tie each side of the twisted pair shielded cable to the two inputs and the shield to the signal ground The importance of using signal ground cannot be overstated most noise and washing displays are a result of indiscriminate grounding The minimum voltage signal for full X deflection is 2 V
30. do not disappear immediately when power is shut off Use extreme caution when throubleshooting the board For troubleshooting the 7007165 may be operated outside its normal mounting position by laying the board flat and reconnecting the four cable connectors Ensure that the etch side of the module does not touch the chassis causing short circuits by insulating the board with a book or piece of cardboard as shown in Figure 4 4b NOTE When placing the 7007165 back into the unit ensure that the bottom of the circuit board rests in the slotted groove insulator block provided on the bottom chassis 12 0331 Figure 4 3 7007165 Power Regulator Assembly 4 7 a Remove power cord and all connectors to the 7007165 Unscrew mounting screws from the opposite side of the vertical chassis wall b Reconnect connectors and place a cardboard under the 7007165 to prevent shorting out the circuit against the chassis when troubleshooting the board outside the unit Figure 44 7007165 Removal 4 8 4 3 3 Regulator Heat Sink Removal To remove the regulator heat sink Figure 4 5 proceed as follows 1 Remove the 7007165 See Paragraph 4 3 2 for instructions Remove the four heat sink mounting screws on the right chassis wall when viewed from front Lift the heat sink assembly straight out To remove a faulty transistor s unscrew the two 6 32 screws holding the transistor s down then pull the transistor s straig
31. e a high impedance The current must flow through R10 and R31 This occurs only if the feedback voltage is a negative value because R10 R31 is tied to pin 10 which is O V so pin A must be negative In fact if 1 mA flows through R10 and R31 the feedback voltage must be 3 2 V and negative The 3 2 V originates from the 0 5 Q resistor in series with the yoke therefore 3 2 V divided by 0 5 Q current is flowing through the yoke This of course is 6 4 A which is an excessive amount of voltage and current limit circuits explained later would probably be called into action to limit the output transistors 3 1 The remaining transistors on the A225 boost the current from E2 to a sufficient drive level to operate the power transistors on the large heat sink The output of E2 drives through its base resistor R14 Q1 serves two pur poses a stage of inversion and a level shifter Inversion is necessary to get the final output in the proper polarity for negative feedback Level shifting is required to drive Q2 at its base voltage E2 cannot do this alone The Q1 stage has no voltage gain but has current gain Q2 however has voltage and current gain and is where the true output voltage is first generated Q2 is a grounded emitter amplifier where in this case the emitter although tied to 22 V can be considered grounded and the collector resistor R23 is not tied to 22 V but for analysis tied to 44 V Q2 has the capability of sw
32. ecessary voltages 80 V that keep the CRT shut off drain to 0 V faster than the high voltage supply When the grid to cathode voltage becomes more positive than cut off the CRT turns on very hard D2 and prevent this from happening When power is turned off the 80 V goes to 0 V but in so doing C1 hangs on to its voltage 60 V and thus back biases D2 which does not allow C1 to discharge momentarily acts like Q1 s power source allowing the emitter and CRT cathode to hold at 62 V which is the safe or off condition Eventually C1 discharges however by that time the high voltage has also discharged rendering the CRT safe 3V PEAKING CIRCUIT O 9602 1 SINGLE O SHOT 3 6 LIGHT PEN AMPLIFICATION The input from the 375 Light Pen that results from detection of beam intensification is not usable in its analog form it must first be converted to a TTL compatible signal This is the prime function of the G840 Light Pen Amplifier module drawing D CS G840 0 1 and Figure 3 7 In relation to the G840 the light pen phototransistor acts as a variable resistor that presents a low going signal at the input J1 pin 3 to the module when screen intensification occurs within the light pen s angle of acceptance This negative going analog signal is inverted by 1 and peaked by the circuit at the collector of Q1 The signal now positive going with a greatly decreased rise time about 1 us is differentiat
33. ed before being input to the LM 306 Comparator The LM 306 is a high speed voltage comparator designed to produce a sharp edged TTL compatible output when the input attains a predetermined threshold voltage In this application the input to the LM 306 pin 2 is held at about 400 mV When the differentiated input at the 5 400mv NZ VOLTAGE 1 COMPARATOR DIFFERENTIATOR ENABLE L LIGHT PEN PULSE L ee 0759 Figure 3 7 Light Pen Amplifier 3 13 input reaches this threshold negativegoing output signal is produced at pin 7 provided an ENABLE signal is present at E3 pin 13 This qualifying signal ensures that all light pen hits LIGHT PEN PULSE L from the G840 are valid inhibiting those hits that might be generated by spurious noise from the light pen The LM 306 output occurs about 30 ns after the two input voltages compare fall time is approximately 20 ns and remains low as long as the input stays above the 400 mV threshold This assertion time is indicated in Figure 3 7 as tl Positive feedback is provided from the output to the input to assist the input signal comparison The negative going output from the LM 306 triggers one stage of a 9602 Monostable Multivibrator which in this application functions as a single shot to produce a 150 ns output signal LIGHT PEN PULSE L Coincident with this signal from the 0 output the 1 output from the first stage of the 9602 triggers the second s
34. edance 5 minimum 3 Input sensitivity 500 mV inch maximum 200 mV inch with resistor change 1 2 4 Common mode rejection ratio 40 dB 5 Maximum operating input 6 V Maximum oper ating input is the sum of the common mode input and the differential input 6 Input offset not to exceed 1 2 peak to peak input signal 7 Maximum nonoperating input 50 V c Full screen deflection and settling time to within 1 spot diameter lt 18 us d Small signal settling time to within 1 2 spot diameter lt us for a 0 1 inch deflection e Small signal linear slew rate gt 0 4 inch 1 us f Velocity error coefficient 500 ns maximum average ramp delay between input and output Z Axis on VR14 without Light Pen Option a Z Input A negative transition from 2 2 4 V but not exceeding 8 V to lt 0 8 V but not more negative than 4 V in 2 20 ns causes an unblanking pulse at the CRT cathode from approximately 62 V to ground with a duration of 2 200 ns at the 50 percent points Delay between the 50 percent point of the negative input transition to the 50 percent point of the output pulse is less than 100 ns Driver must sink 4 mA b Z Direct A positive going pulse not exceeding 65 V but at least 45 V in height and not exceeding 10 us but at least 1 in duration unblanks the CRT to a viewable intensity This signal is ac coupled to the CRT grid Channel Select With the Channel Select Switc
35. ee oe ee e bo 2 7 Brig tnessControl poa a Q s gea ow ee SE ee 3 12 VR14 VR17 Voltage Check Points 4 2 VRI4 Engineering Drawings 5 1 VR17 Engineering Drawings 5 1 iv WARNING Maintenance procedures should be performed by qualified service personnel only High voltages are present within the unit and under certain conditions are potentially dangerous All electrical safety precautions must be observed Inherent implosion protection is employed in the CRT design however the tube may be damaged if it is subjected to rough treatment or dropped while being removed from or installed in the display Exercise caution during these operations 1 1 INTRODUCTION The VR14 and VR17 are completely self contained CRT display monitors that require only analog X and Y position information and an intensity input to generate sharp bright displays The VR14 and 17 are electrically identical The VR17 however has a larger display screen 17 inches diagonal than the VR14 12 inches diagonal This necessitates a correspondingly larger enclosure and a CRT support bracket for the VR17 Except for the CRT itself both VR14 and VR17 are composed of fully solid state circuits utilizing high speed magnetic deflection to enhance brightness and resolution The inputs for the X and Y deflection may be balanced or single
36. ence ground Not Used J17 24 Pin Connector Pin 15 J18 Pin 4 Pin 16 N C Pin 17 J18 Pin 5 Pin 18 J18 Pin 6 Pin 19 1 20 J18 Pin 12 21 N C Pin 22 J18 Pin 8 Pin 23 J18 Pin 10 Pin 24 J18 Pin 9 Table 2 1 Cont 317 Rear Connector Pin Assignments VR14 Not Used Not Used Not Used Not Used Not Used 22 V is available if J18 Pin 8 is jumpered to J18 pin 1 22 V is available if J18 pin 10 is jumpered to J18 pin 3 J18 pin 9 must be jumpered to J18 pin 2 Bell Speaker KB Signal KB Signal Light Pen Out 5 VIN VRIAL VRI7L Function Used in LK40 option Used in LK40 option Used in LK40 option Amplified light pen pulses Used in LK40 option 22 V is available if J18 Pin 8 is jumpered to J18 pin 1 22 V is available if J18 pin 10 is jumpered to J18 pin 3 J18 pin 9 must be jumpered to J18 pin 2 Table 2 2 J18 Rear Connector Pin Assignments J18 14 Pin Connector Signal Name Pin 1 22 V Regulated Pin 2 GND Pin 3 22 V Regulated Pin 4 117 Pin 15 Pin 5 J17 Pin 17 Pin 6 J17 Pin 18 Pin 7 N C Pin 8 J17 Pin 22 Pin 9 J17 Pin 23 Pin 10 J17 Pin 24 Pin 11 N C Pin 12 J17 Pin 20 Pin 13 GND Pin 14 22 V along with the deflection signal from where it is generated a quasi differential signal is generated Instead of termi nating this ground at the VR14 VR17 chassis use the ground as if it were one side of a differential signal the other si
37. ended bipolar or offset and positive or negative going without any modification to the VR14 VR17 The VR14 and VR17 come in several configurations listed in Table 1 1 Table 1 1 VR14 and VR17 Configurations pel Designation Light Pen Option VR14 0 VR14 A No VR14 B No VR14 C No VR14 D No VR14 E No VR14 LC Yes VR14 LD Yes VR17 LC Yes VRI7 LD The VR14 versions without the light pen option contain a W682 Intensity Control Circuit Board and a G838 Fault Protection Circuit Board as well as a front panel CHANNEL switch which operates with the W682 board In CHAPTER 1 GENERAL INFORMATION 1 1 this variation intensity pulses may be time multiplexed or gated by a separate input to allow the screen to be timeshared by two inputs The VR14 VR17 versions with the light pen option VR14 LC VR14 LD VR17 LC VR17 LD do not have this timesharing capability nor channel selectivity They contain a W684 Intensity Control Circuit Board in place of the W682 and a G840 Light Pen Amplifier in place of the G838 The G840 circuit board however contains the fault protection circuitry of the G amp 38 board 1 2 SPECIFICATIONS VR14 VR17 specifications are as follows Physical VR14 VRI7 Height 10 1 2in 267 mm 15 381 mm Width 19 in 483 mm 21 1 2 in 546 mm Depth 17 in 432 mm 27 in 686 mm Weight 75 16 34 kg 85 Ib 39 kg Viewable Area 6 3 4 in X 9 in 8 1 4 in X 11 in 171 45
38. ge See Paragraph 2 5 and Table 2 2 for proper settings CHAPTER 2 OPERATION 115 Vac TB1 jumper jumper 230 Vac TB1 100 Vac jumper Interchange Interchange Orange with White with Red from Gray from Transformer Transformer Figure 2 1 Input Power Jumper 2 2 FRONT PANEL CONTROLS The on off brightness control and the channel select control not applicable to VR14L VR17L are located on the front panel The on off switch turns on input power to the VR14 VR17 when the knob is rotated clockwise from the maximum counterclockwise off position Turning the knob clockwise also increases the brightness of the dis played information A delay of about 30 seconds occurs before information appears on the screen while the CRT filament warms up In an operating system it is recom mended that power be left on the display even when it is not in continuous use so that the filament warmup delays do not occur The channel select switch on VR14s without the light pen option works in conjunction with the channel select signal applied at the rear connector When not using the dual channel feature the select switch should be in the 1 amp 2 position When using the dual channel system points on the screen will be intensified from Z intensity inputs only when the channel select signal at the rear connector is high and the channel select switch is in the Channel 1 position If the channel select input signal goe
39. h in the Channel 1 position a positive level of greater than 2 4 V but not exceeding 8 V enables the Z input circuit A level of less than 40 8 V but not more negative than 4 V disables the circuit With the switch in the Channel 2 position a positive level disables the Z circuit a negative level enables it Placing the switch in the Channel 1 amp 2 position disables this input Z Axis VR14 VR17 with Light Pen Option VR14L and VR17L a Z Input This is a TTL logic signal When a low it unblanks the CRT by causing the cathode voltage to change from approximately 62 to ground The CRT will remain unblanked as long as the Z input is at a logic low b Intensity O 1 2 These three signals together with the brightness control generate a voltage of from 80 V to on the CRT grid 1 to determine image brightness The combination of the three intensity signals asserts one of eight possible analog voltages which in turn is ANDed with the output of the brightness control to generate a grid voltage in the 0 to 80 V range Thus there are eight intensity levels at each of the infinite positions of the brightness control Power a All power supplies necessary for operation of the unit are self contained b Input Requirements Voltage Selectable by tap changes 100 V 10 115 V 10 230 V 10 Frequency 50 60 Hz Power lt 500 W Current lt 5 A Type Single Phase
40. he 2N4399 s collector is also tied to the output the yoke it also supports the output current and in fact becomes the primary source of output current Depending on Q3 s demands the 2N4399 is completely slaved to Q3 If Q3 turns on harder so does the 2N4399 If Q3 shuts off so does the 2N4399 Therefore the output looks like it is an emitter follower Q3 but the 2N4399 delivers all the current and handles the necessary power dissipation re quirement 3 2 To minimize power consumption the output would like to operate in Class B i e while positive current is required no negative current transistors should be turned on and vice versa However this approach creates problems at the point where the transition between positive and negative current takes place The reason is that one set of transistors does not shut off exactly where the other set takes over but instead shut off prematurely This creates a dead zone or man s land where neither the positive nor the negative transistors are on and controllable The appearance on the CRT screen of such a phenomenon is a bunching or nonlinear compression of displayed information where it occurs usually near the center of the screen This problem can be solved by not allowing the positive transistors to shut off at zero but rather conduct somewhat into the opposite side s region In so doing the positive transistors would not shut off for example until the negative transistor
41. he W682 W684 card When not intensifying the cathode is held at 62 V The 62 V is derived from the 80 Vdc at the W682 W684 When the beam is to be turned on the 62 V on the cathode is grounded or made V However this alone does not determine brightness since intensity is related to grid to cathode voltage Thus the cathode is constantly going between 62 V and 0 V but depending on where the grid voltage brightness potentiometer is set the beam may never be on dim or very bright Grid 2 of the CRT is operated at approximately 400 Vdc The 400 V is generated from the 150 Vac tap of the power transformer by a voltage doubler on the G836 board The ac passes through C14 and is prevented from going negative by D9 This causes the entire peak to peak voltage to become positive D10 rectifies this voltage and C15 filters it the resultant output is 400 Vdc The 400 Vdc goes directly to grid 2 If grid 2 is not substantially positively biased the CRT beam can never be turned on regardless of how much grid to cathode drive occurs The 400 Vdc also goes to one side of the focus potentiometer R35 on the G836 board The other side of the potentiometer goes to 80 Vdc The wiper goes to the focus electrode on the CRT Because of CRT manufacturing tolerances proper focus may occur from unit to unit anywhere between 3 6 80 Vdc and 400 Vdc The anode is supplied 10 5kV from the high voltage supply 3 4 HIGH VOLTAGE POWER
42. ht out from the socket Apply an even coat approximately 1 32 inch thick of thermal compound to all mating surfaces of the new transistor Replace the new transistor ensuring that the base and emitter pins are oriented properly otherwise the transistor case will not align with the two screw holes Also ensure that the insulating washer is between the transistor and the heat sink and that each mounting screw has a star washer 4 3 4 Yoke and CRT Removal To remove the yoke proceed as follows 1 Remove the line and all the circuit modules G838 G840 A225 W682 W684 along with the plastic CRT socket cover Carefully remove the yoke cable connector from its mating connector on the inner side of the circuit board mounting bracket Using a screwdriver loosen the screw that holds the yoke neck clamp by inserting the nut driver through the access slot provided in the CRT shield Loosen sufficiently for the yoke clamp to be slipped off the yoke Carefully remove the CRT socket connector and slide the yoke clamp off the CRT neck Slip the yoke connector through the access slot in the CRT shield and pass it along with the entire yoke assembly off the CRT neck and out the rear Sometimes the yoke gets stuck at the socket end of the CRT because the yoke plastic mounting piece hugs the CRT neck tightly and must be spread to pass over the CRT socket To remove the CRT proceed as follows 1 Remove the yoke first
43. inging its collector almost a full 22 V This large swing is necessary for the yoke which must swing as close as possible to the 22 V The reason for this will be explained later The collector of Q2 drives Q3 and Q4 which are emitter followers for the positive and negative outputs Since a low output impedance is necessary emitter followers are used however Q3 and Q4 are not capable of handling the output power necessary since each can only drive 0 5 A A bootstrap power stage is used to raise the emitter follower current capability to the 4 A required This is accom plished with two power transistors on an external forced air cooled heat sink These external transistors are essentially slaved to the Q3 and Q4 emitter followers Because the positive swing and negative swing work in the same way only the positive is described When the amplifier is required to deliver positive current in the yoke the circuit responds by turning Q2 on thus placing a positive voltage on the base of Q3 Q3 s emitter responds in a similar manner however it cannot supply the necessary yoke current Still Q3 attempts to deliver the necessary current Unlike a normal emitter follower Q3 s collector is not tied to 20 V but instead to the base of the 2N4399 Power Transistor Thus when Q3 tries to deliver the output current from its emitter this very current must flow into Q3 s collector from the base of the 2N4399 which will now turn on Because t
44. lished by the resistor ratios of R7 to R4 and R6 to R5 The bandwidth of the amplifier is tailored by C5 and C6 which act internally on the integrated circuit and C13 and C14 which act at high frequency to roll off the low frequency gain established by the R7 to R4 and R6 to R5 ratios A 6 V is generated for both El and 2 from the 22 V This is done by dropping resistors R18 and R19 and Zener diodes DS and D6 and and C2 and C4 are local high frequency bypass filters for the 6 V to reduce any high frequency signal noise at each operational amplifier thus avoiding the possibility of parasitic oscillation The single ended output of El is conducted to R11 which is the input to the actual deflection amplifier El serves more as a signal conditioner preamplifier The amplifier is essentially an inverting voltage to current amplifier i e an input voltage is converted to an output current 180 out of phase or inverted with respect to this input Because the input is a voltage however the output current must be converted back into a voltage in order that the feedback compare volts with volts Current is converted to voltage with a 0 5 Q resistor in series with the yoke voltage across this resistor is an exact replica of the current flowing in the yoke thus the amplifier compares the input voltage with the yoke current to ensure that the yoke CHAPTER 3 THEORY OF OPERATION current is an exact replica of the input
45. ll the transistor straight out from the socket Apply an even coat approximately 1 32 inch thick of thermal compound to all mating surfaces of the new transistor Replace the new transistor making sure that the base and emitter pins are oriented properly otherwise the transistor case will not align with the two screw holes Also ensure that the insulating washer is between the transistor and the heat sink and each mounting screw has a star washer 4 3 2 7007165 Power Regulator Assembly Removal The 7007165 Power Regulator Assembly comprises a G836 regulator printed circuit board with a mounting frame for J1 J2 J3 and J4 To remove the 7007165 Power Regulator Assembly proceed as follows 1 Remove the line and all circuit modules G838 G840 A225 W682 W684 2 Remove all four cable connectors Figure 4 3 coming into the connector bracket on the 7007165 by squeezing the two locking tabs on the sides of each connector while pulling the connector straight up allowing the locking tabs to pass through the square holes they were butted against Do not pull the connector by its wires only by its plastic body TO VR14 TO DIODES TO TRANSFORMER AND FILTERS Remove the two mounting screws for the 7007165 from the opposite side of the 7007165 chassis wall The 7007165 is now free and may be pulled straight out WARNING The 7007165 has 80 Vdc 80 Vdc and 400 Vdc available on it These voltages
46. n or ground et J17 24 Pin Connector Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8 Pin 9 Pin 10 Pin 11 Pin 12 Pin 13 Pin 14 L Z Select X Input X Input X Signal GND Y Input Y Input Y Signal GND Z Direct Table 2 1 117 Rear Connector Pin Assignments VR14 High input enables Z intensify to occur if channel select switch on 1 A low input enables Z intensify to occur if channel select switch on 2 Not Used Not Used When this input goes from high to low an intensify pulse is generated One side of X input signal line Other side of X input signal line ground for single ended input X signal reference ground One side of Y input signal line Other side of Y input signal line ground for single ended input Y signal reference ground Input signal that directly modulates CRT grid ac coupled Intensity 2 Intensity 0 Intensity 1 Z Input X Input X Input X Signal GND Y Input Y Input Y Signal GND VRIAL VRI7L Function Determines intensity level Determines intensity level Determines intensity level When this input is low an intensify signal is applied to the CRT One side of X input signal line Other side of X input signal line ground for single ended input X signal reference ground One side of Y input signal line Other side of Y input signal line ground for single ended input Y signal refer
47. nd vertical gain on the right The two rear potentiometers are the hori zontal position on the left and the vertical position on the right The gain adjustments allow the VR14 VR17 to accom modate a range of input signal amplitudes and expand or contract the horizontal and vertical deflection to suit full screen requirements The position controls accommodate a variety of input signals and allow offset inputs to be centered on the CRT screen Once initially adjusted for the particular input signals used the gain and position controls rarely have to be adjusted Gross positioning off screen or excessive gain deflecting off the extremities of the screen should be avoided since the deflection amplifiers will go into current limiting and may overheat if allowed to stay in this condition any length of time Turning the X and Y gain controls clockwise increases the gain or displayed image size Turning the X and Y positions clockeise moves the displayed information right and up respectively The focus and brightness preset adjustments are located at the top right central portion of the unit They are on the power supply regulator circuit G836 that is somewhat recessed from the top of the unit The brightness preset is the rear most of the two This potentiometer allows the range of the front panel brightness control to be limited to any maximum brightness desired Turning the brightness preset counterclockwise increases the maximum brightne
48. ness Positive going signals increase brightness This input is not direct coupled therefore de brightness information cannot be used The RC time constant is approximately 30 ms The Z direct may be used with or without the Z intensify input If Z direct is used with Z intensify it can alter the brightness of the normal intensify pulse by adding or subtracting at the CRT grid This is accomplished by pulsing the Z direct with a pulse of equal duration with the Z intensify By varying the amplitude and polarity of the Z direct pulse the dot will be of a different brightness When using Z direct without the Z intensify such as for vector intensity control or any other non point plotting application the signal must be large enough to overcome the CRT cutoff A typical direct signal will have 5 V to 10 V of actual brightness information riding on top of a 40 V pedestal the 40 V pedestal ensures that the CRT will reside below cutoff The Z select input applicable only to VR14s without light pen option works in conjunction with the front panel channel select switch The Z select allows the Z intensify pulse to be gated or time multiplexed When the channel select switch is on the 1 amp 2 position Z select inputs have no effect on the VR14 When the channel select switch is in the 1 position Z intensification occurs only when Z select input is a TTL high When the channel select switch is at 2 Z intensification occurs only when Z select
49. nly half deflection is working no positive current or no negative current C 1 APPENDIX C A225 REPAIR capability and the power transistors are operating properly Q3 should be replaced for no positive current and Q4 for no negative current Also check R26 and R27 for burns These resistors overheat if the deflection amplifier is operated in the fault current limit condition for any length of time Finally if C9 become shorted R9 or 10 respectively will burn out Check C9 or C10 with an ohmmeter to verify this type of failure V R14 VR17 CRT DISPLAY MONITOR USER S MANUAL EK VR14 OP 005 READER S COMMENTS Your comments and suggestions will help us in our continuous effort to improve the quality and usefulness of our publications What is your general reaction to this manual In your judgment is it complete accurate well organized well written etc Isit easy to use What features are most useful What faults do you find with the manual Does this manual satisfy the need you think it was intended to satisfy Does it satisfy your needs emmm Why Would you please indicate any factual errors you have found Please describe your position Name Organization Street _ 0 Department City State FN Zip or Country FIRST CLASS PERMIT NO 33 MAYNARD MASS BUSINESS REPLY MAIL NO POSTAGE STAMP NECESSARY IF MAILED IN THE UNITED STATES Postage will be paid by Digital Equipmen
50. oard The G840 contains the G838 circuitry as well as an amplifier to detect and shape pulse outputs from the light pen The output of the light pen amplifier is brought out of the VRIAL VRI17L through pin 19 of the 24 contact amphenol connector J17 at the rear of the display monitor Note that in the VR14L and VR17L the W684 intensity control replaces the W682 The W684 allows an intensity pulse to the cathode whose duration is equal to that of the Z intensify signal The W684 circuitry also modifies the grid 1 bias voltage thereby allowing eight intensity levels for a particular setting of the front panel brightness control All other circuits represented in Figure 1 2 are identical to those represented in Figure 1 1 ri CHANNEL 1 FROM THERMAL CUTOUT 115 145 UNIT POWER RECTIFIERS FILTER POWER TRANSFORMER CHANNEL 2 gt oL o 2 INTENSITY INTENSITY 682 Tezy FAULT PROTECTION 22 v G838 X INPUT Y INPUT 145 VAC FAN 22V PASS 22V PASS p THERMAL RANSISTORS TRANSISTORS Es CUTOUT 115 22V 22 HIGH POWER SUPPLY amp FOCUS VOLTAGE REGULATOR BOARD POWER 6836 400V SUPPLY 80V 80V 10 500VDC CHANNEL BRIGHTNESS ANODE SELECT Y BRIGHTNESS Focus NGHTNE FOCUS ad 62 FOCUS DEFLECTION 80V gt FEEDBACK 0 5 0 CURRENT SAMPLE x DEFLECTION AMPLIFIER A225 Y 22V DEFLECTION 6 22 AMP
51. pin 02 or 03 has voltage The 02 X axis transis tors are on the right side of the heat sink assembly when viewed from the front of the VR14 VR17 03 Y axis transistors are on the left side In both cases a plus voltage at 02 or 03 means the PNPs 2N4399 at fault These are the lower transistors on both sides If the voltage APPENDIX B DEFLECTION AMPLIFIER B 1 TROUBLESHOOTING at 02 03 is minus the NPNs 2N5302 are faulty These are the upper transistors on both sides If readings are observed at 02 03 when the A225 boards are removed then the deflection fault is on the boards themselves assuming of course proper input signals are applied and all power supply voltages are nominal If the yoke current goes full negative only when the A225 card is plugged into that axis the most likely suspect is the 2N2904A Q2 If one axis is faulty a quick check can be made by swapping the X and Y deflection boards A225 to see if the faulty axis follows the circuit board in question After the power supply deflection power transistors have been proven sound incorrect deflection coil current readings may be isolated to the A225 circuit board itself If when the A225 is plugged in the deflection current goes full negative about 4 V as measured at 02 for X for Y and not controllable Q2 has probably opened and should be replaced If o
52. rom 0 through 7 The higher the brightness level the more positive the emitter of Q5 and therefore the harder Q5 conducts As Q5 conducts harder more voltage is dropped over the Q4 R18 R19 and R29 network causing the base of Q3 to become more positive This in turn decreases Q3 conduction and the emitter grid 1 voltage approaches V Figure 3 6 illustrates the relationship between the eight brightness levels that are program controlled and the brightness control which can be changed by the operator Reference A shows the relative brightness at a particular brightness control setting for each of the brightness levels As the control is turned clockwise there is a linear increase in brightness at each level reference B The contrast control R19 is positioned between Q4 and Q5 As the control is turned clockwise dropping more voltage the brightness range between brightness level 0 and brightness level 7 is increased i e the image contrast is increased This is indicated in Figure 3 6 as the change from reference A to reference C the original brightness spread x is increased Actually level becomes dimmer and level 7 becomes brighter Therefore the brightness control IMAGE BIGHTNESS must also be adjusted at the same time to compensate for the decreased lower intensity levels Reference D shows the result of this final adjustment Note that grid 1 voltage is the consequence of the three intensity level
53. rs the left side of the screen is controlled by the left lower power transistor if the deflection heat sink is viewed from the front of the VR14 VR17 the lower part of the screen is controlled by the right lower power transistor Of course the upper and right are controlled by the NPN 2N5302 the right side of the heat sink controlling the upper screen the left side of the heat sink controlling the right screen The remaining possible faulty picture patterns such as picture swim 60 Hz oscillations distortion etc will be restricted generally to improper input signals especially grounding techniques or faults on the A225 circuit board If input signals are not suspect a faulty A225 may be isolated by swapping X and Y A225s with one another to see if the problem changes axis 4 5 d Ifa weak picture that is deflected off the screen on all sides is encountered with excessive jitter and ripple the high voltage supply should be replaced 4 3 ASSEMBLY REPLACEMENT INSTRUCTIONS Other than the G838 G840 A225s and W682 W684 circuit modules most repair and replacement will involve the G836 regulator subassembly the regulator heat sink assembly and the deflection heat sink assembly and in rare cases the high voltage assembly yoke and CRT It cannot be stressed too strongly that the VR14 VR17 line cord be removed from the line before doing any mainte nance Turning power off or removing fuses does not render the uni
54. s generating a brightness level one of eight that is then combined with the particular brightness control setting At the same time the contrast control setting determines the difference in brightness between the bright ness levels Table 3 1 Brightness Control Front Panel Brightness Control Intensity Level Brightness SNOOP WN O A a r In case of a decrease in the 5 or 80 V input to the W684 the cathode and grid circuits described above are disabled If these circuits were not shut off when this low voltage condition occurred the phosphor would be burned and the screen damaged This is because X and Y deflection circuits are disabled by the same power failure and the electron beam would be continually directed to the same spot on the screen If the 5 V input from the G840 at pin A drops to about 4 V Q9 loses forward bias and ceases to conduct CP 0584 Figure 3 6 VR14L VR17L Brightness and Contrast Control 3 12 Effectively this opens the 5 V input to the emitter of Q7 cathode circuit and to the R21 R22 and R23 voltage divider grid 1 circuit The same result occurs if the 80 V input to the cathode circuit fails In this instance the base of Q9 becomes more positive Q9 is cut off and the 5 V input opens When power is removed from the VR14L VR17L the CRT must be prevented from blooming and possibly burning the phosphor Blooming can occur because the n
55. s low while the select switch is at 1 intensification ceases On the other hand the Channel 2 position works in the opposite manner If the channel select input signal is low and the select switch is at 2 Z intensification signals will intensify on the screen Thus if a group of information points is to be separated from another group separation can be achieved by having group intensification pulses occur only when the Z select line is high and group 2 intensification pulses occur only when the Z select line is low Channel select position 1 amp 2 overrides the select input signal and displays every intensifi cation pulse of both channels at once To observe only Channel 1 information select Channel 1 and all Channel 2 signals are locked out By selecting Channel 2 only Channel 2 signals are displayed 2 3 REAR PANEL CONNECTORS The rear panel has an Amphenol 14 contact connector J18 and an Amphenol 24 contact connector J17 Tables 2 1 and 2 2 list rear connector pin assignments 2 4 INTERNAL CONTROLS The VR14 VR17 internal adjustments include six potenti ometers X position X gain Y position Y gain focus and brightness preset Access to the adjustments is gained by removing the case cover Figure 2 2 The gain and position adjustments are located on the top left central portion of the VR14 VR17 as viewed from the front The two forward potentiometers on the deflection circuits are the horizontal gain on the left a
56. s viewed from the front of the VR14 VR17 The 22 V is controlled by the NPNs 2N5302 on the rear section of the regulator heat sink If after replacing the power transistors the problem is not corrected the G836 board itself is suspect If the APPENDIX A POWER SUPPLY TROUBLESHOOTING regulator circuits are not working the output could be beyond its nominal value The MC1709 is the most likely suspect followed by the drive transistors Q3 for 22 V and Q1 for 22 V If on the other hand the 22 V read zero the same power transistors are still suspect they may be open Also in this case if the two 1N4001 diodes used as current limiting for the power transistors are shorted the power transistors cannot receive base current and thus will not turn on rendering their output To check for this condition turn off the power and measure resistance with a VOM set at RX1 across D15 and D16 if the 22 V was 0 and D13 and D14 if the 22 V was 0 The resistance with the VOM lead connected either way should always be above 5 Q When the deflection circuit cards A225 are removed their respective power transistors receive no drive and therefore are off When monitoring 02 X yoke current sample and 03 Y yoke current sample no reading should be observed Any voltage at these points indicates a power transistor is on by itself Generally this transistor is shorted To determine which transistor is faulty observe which
57. s were well turned on Thus the amplifier would have control to cancel any nonlinearities that might occur This task is accomplished with R23 R26 R27 The major influence is R23 because it places voltage between Q3 and Q4 bases which allow one to be on a little into the conduction region of the other If R23 were 0 the dead zone would be very abrupt causing maximum distortion On the other hand as R23 is increased the transistor conducts further and further into the opposite side s operating region This creates two major problems The power dissipation causes excessive heating of the output stage and the extra current required overloads the power supply The value of R23 is chosen therefore to minimize dissipation but also to minimize the cross over distortion The output at the yoke has the capability of swinging a full 22 V This is necessary because even though the yoke is less than 0 1 Q at dc it has inductance thus to force current through at high speeds requires a lot of voltage V L Aiyat To change 2A through 20 in 2 us requires 20 V That is why the A225 not only has to boost the input signal to a large current but also has to have good voltage capability to force the yoke current to change quickly Position control in the A225 is accomplished by adding another input to E2 exactly the way the signal comes in This is accomplished with R9 The position signal is nothing more than an adjustable dc level from R8
58. screen cannot be accomplished A 3 V peak to peak deflection signal for example may not be offset from O by more than 1 5 V So 1 5 V 0 V to 3 V or to 3 V are all acceptable but a deflection input that goes from 1 V to 4 V cannot be used until it is shifted down a minimum of 1 V Table 2 3 summarizes the control settings for various inputs Table 2 3 Control Settings Input Deflection Position Setting 2 05 With inputs set and 0 0 center position potentiometers to get 2 V to 5 V is up 0 V at 02 for X and A03 A and to right for Y 0 V to 2 V to 5 V With no inputs set 2 2 V 0 0 upper right 02 with X and screen Y position potentiometers 0Vto 2Vto 5V 0 0 lower left With no inputs set 2 2 V 02 03 with X and Y position potentiometers The Z intensify input requirement is simply a TTL transi tion from high to low In VR14s using a W682 Intensity Control this triggers the intensity circuit to generate a 300 ns intensify pulse In VR14Ls and VR17Ls which use the W684 Intensity Control the intensify circuit is trig gered and remains active until Z intensify goes high NOTE The intensify signal must be delayed from the X and Y position signal for an appropriate length of time to allow the deflection coil to settle the electron beam to its required posi tion Failure to do so displays smeared dots that are located incorrectly on the screen
59. ss range of the front panel control Generally this control is set so that at maximum brightness setting on the front panel knob the displayed information does not bloom causing a degradation in resolution The focus potenti ometer is in front of the brightness preset The adjustment is quite insensitive and requires several turns to go through focus The VR14L and VR17L also contain a contrast adjusting potentiometer R29 located on the W684 module It is accessible from the top of the VR14 VR17 This control is used to extend or contract the brightness range of the CRT display It does not normally have to be changed after an initial adjustment is made to compensate for component variations 2 5 INPUT SIGNAL REQUIREMENTS NOTE The deflection amplifiers must not be driven so that the CRT beam is off screen for any length of time or permanent damage may occur Ensure that input deflection signals fail to a safe on screen value The VR14 VR17 requires analog voltage inputs for X and Y deflection and a logic level change or pulse for intensify The X and Y inputs are identical However because the CRT is a 3X4 rectangle only 3 4 of the horizontal deflection is required for full vertical deflection The deflection inputs are differential but may be driven from single ended sources When using single ended sources the differential input is helpful in eliminating annoying ground loops and hum By carrying the local commo
60. supply from TB2 of the right side chassis Remove the cast bezel by removing the three right and left retaining screws Remove the two side and two bottom high voltage assembly mounting bracket screws and remove the high voltage assembly out toward the front of the unit Each 14 17 is shipped with a current set of engineering drawings If any discrepancies exist between the schematics in this manual and those delivered with the unit the set of drawings shipped with the unit should be considered the most accurate Tables 5 1 and 5 2 list the drawings shipped with the VR14 and VR17 respectively Table 5 1 VR14 Engineering Drawings Drawing No Drawing Directory B DD VR14 0 Engineering Specification A SP VR14 04 Block Schematic D IC VR14 0 1 Module Utilization C MU VR14 0 3 Module Utilization A PL VR14 0 3 Circuit Schematic G836 D CS G836 0 1 Circuit Schematic G840 D CS G840 0 1 Circuit Schematic G838 B CS G838 0 1 Circuit Schematic PL A PL G838 0 0 Circuit Schematic A225 D CS A225 0 1 Circuit Schematic W684 D CS W684 0 1 Circuit Schematic W682 B CS W682 0 1 Circuit Schematic PL A PL W682 0 0 Cable Keybd Interlock C IA 7009248 0 0 Circuit Schematic Heat Sink Circuit Schematic Deflection Circuit Schematic Power Supply C CS 7007080 0 1 C CS 7007082 0 1 D CS 7007084 0 1 VR14 Display Assy D UA VR14 0 0 VR14 Display Assy PL A PL VR14 0 0 Wired Assy D AD 7007078 0 0 Wired Assy PL A
61. t Corporation Technical Documentation Department 146 Main Street Maynard Massachusetts 01754
62. t off and Q7 conducts With 7 conducting 5 REG is coupled to the base of Q2 causing it to conduct The cathode voltage goes from 62 to 0 V and a beam can be produced provided one other condition is satisfied grid 1 must be sufficiently positive before the grid to cathode voltage results in a beam strong enough to cause screen fluorescence Grid voltage can be varied from approximately 80 to almost brightness increases as the voltage becomes more positive Q3 controls the grid voltage with the screen brightest when Q3 is cut off When Q3 conduction increases the image becomes dimmer Conduction of Q3 is determined along with the contrast control setting by the voltages present at the base of Q4 and the emitter of Q5 The voltage at the base of 4 is established by the front panel brightness control Turning this control clockwise causes Q4 to conduct less the emitter voltage becomes more positive As a result the base of Q3 becomes more positive Coincident with this the emitter voltage of Q5 is determined by the state of the three intensity level signals Intensity 2 0 L These signals forward bias three diodes D8 D9 and D10 that control the conduction of 5 REG through a voltage divider consisting of R21 R22 and R23 Table 3 1 shows the relationship between the three inten sity levels and the resultant brightness level As the number of levels asserted increases from 0 through 3 the brightness level increases f
63. t safe from shock hazards since the power switch and fuse interrupt only one side of the ac input line voltage the other side is permanently connected as long as the line cord is plugged in Do not take chances UNPLUG the line cord NOTE Photographs in this section are of a VR14 prototype but generally apply to all VR14 and configurations 4 3 1 Deflection Heat Sink Removal To remove the deflection heat sink Figure 4 2 proceed as follows l Remove the line cord and all circuit modules above the deflection heat sink assembly G838 G840 A225s W682 W684 2 Remove the four 6 32 screws that hold the heat sink assembly to the rear chassis plate 3 Lift the assembly out to make room for removing the assembly cable connector The 15 pin connector is removed by squeezing the retaining tabs on each side of the connector so that when the connector is pulled the tabs pass through the square holes that they were butted against Do not pull the connector by its wires only by its plastic body Remove circuit boards and the four 6 32 screws holding the deflection sink to the rear panel b Remove heat sink assembly and its connectors if necessary and remove faulty power transistor Later models do not have the four BNC connectors at the top rear of the unit Figure 4 2 Deflection Heat Sink Removal 4 6 4 remove a faulty transistor unscrew the two 6 32 screws that hold the transistor down Then pu
64. tage also configured as a single shot The 1 output of the second stage high for 70 us inhibits a second light pen hit immediately following the first one Timing for this operation is shown in Figure 3 8 The comparator output assertion time is unimportant because only the negative going transition is needed to initiate LIGHT PEN PULSE L COMPARATOR OUTPUT E4 7 4 150ns LIGHT PEN PULSE L E1 3 E2 6 E2 10 NOTE In the event of failure of either 22 V supply deflection ceases and a bright spot occurs on the CRT resulting in a burn To prevent this the circuit on the G840 module that produces 5 V for the W684 intensity module will be disabled if either the 22 V or 22 V goes to 0 in the case of a short circuit or blown secondary fuse Referring to drawing D CS G840 0 1 if 22 V fails loses forward bias at the emitter and turns off shutting down the 5 V If the 22 V goes to 0 Q2 loses emitter voltage and the base of Q3 goes high This causes Q3 to turn off and 5 V drops This circuitry aside from some component values is identical to the fault protection circuitry on the G838 Figure 3 5 Note that this failure detection circuit is in addition to the W684 low 5 V voltage protection circuit previously described Paragraph 3 5 3 6 1 375 Light Pen The 375 Light Pen is simply constructed A phototransistor is recess mounted drawings C UA 375 0 0 and D CS 5410268 0 0 in
65. tage drop across D6 and the output of gate C QI s collector is tied through R7 and D8 to 80 Vdc With Q1 off the collector tries to ride up to 80 Vdc but D7 begins to conduct at 62 V clamping the collector at 62 V The 62 V is generated by dropping the 80 V across R8 and Zener diode D14 Q1 s collector is tied through R12 to the CRT cathode Therefore in the absence of an intensify input the cathode resides at 62 V This along with the negative bias on the grid keeps the CRT beam shut off When an intensify signal occurs gate C s output goes high allowing Q1 to receive base current from the 80 Vdc via D17 R11 R5 D13 and D15 This base drive turns on Ql causing its collector and the cathode of the CRT to go from 62 V to O V This turns the CRT beam on The duration of this intensify pulse is determined by the time constant of C2 R4 and is normally 300 ns D16 prevents the voltage supplied to R5 from exceeding 5 V this is necessary to prevent damage to gate When power is removed from the VR14 the CRT must be prevented from blooming and possibly burning the phos phor Blooming can occur because the necessary voltages 80 Vdc that keep the CRT shut off drain to 0 V faster than the high voltage supply When the grid to cathode voltage becomes more positive than cutoff the CRT turns on very hard D8 and C14 prevent this from happening When power is turned off the 80 V goes to 0 V but in so doing C4 hangs on
66. the heat sink adjacent to the G836 Since the 22 V regulators are symmetrical only the negative regulator is described The 43 V is dropped by R33 and R34 and preregulated with D5 and to 12 Vdc and D7 and D8 to 12 Vdc The 12 Vdc are the voltages necessary to operate El and E2 they are also used to generate the reference voltages with which the 3 5 output voltage will be compared The reference for the 22 V regulator is made with the 12 Vdc passing through and establishing 6 2 V across D1 C1 across D1 reduces the dynamic resistance of the reference by removing high frequency fluctuations The reference voltage is delivered to R2 which ties to the summing point pin 2 of operational amplifier El The feedback from the output regulated voltage through R3 is also applied to the summing point of El The nature of the circuit is that a null will be maintained at pin 2 of El Therefore because the voltage on R2 reference is stable the only variable is the output Whenever the output changes for any reason the null is disturbed at pin 2 of El El then forces the output to change in a manner that returns the null For example if the input line voltage increases causing the 43 V to increase the 22 V regu lated output starts to climb The null would then be disturbed and El would shut the output down somewhat so that the null could be maintained On the other hand if a heavy load occurred on the 22 V regulator causing
67. tive going transition is ac coupled through C2 and becomes a positive spike that exponentially decays to 0 The time constant of this decay is determined by C2 and R4 This positive going spike is the input to gate B pins 11 12 and 13 Also as input to B is the channel select information which comes from pin R This information either enables gate B to respond to the intensification spike or not Assuming B is enabled from pin R the positive spike causes the output of to go to a low This low remains as long as the input spike to B is above its 1 or high threshold level As soon as the spike decays below the threshold B s output immediately reverts to the high state B s output is fed back to A s input pin 10 to allow A s output to latch high thus not requiring A s input pin 9 to remain low but rather be a momentary drop from a high Of course when the spike decays at B s input the 3 10 latching input is removed from A pin 9 thus enabling A to respond to the next negative going transition on the Z intensify input 05 clamps the input from going negative during the negative going transition that occurs when A resets Gate C pins 1 2 and 3 simply inverts the intensify pulse to drive the output pulse amplifier Q1 Gate normally is low until a pulse comes along This low grounds out the base drive for Q1 therefore it will be off D13 and D15 guarantee that Q1 will be off even though there is a residual vol
68. to its voltage and thus back biases D8 which does not allow C4 to discharge C4 momentarily acts like Q1 s power source allowing the collector and CRT cathode to hold at 62 V which is the safe or off condition Eventually C4 discharges however by that time the high voltage has also discharged rendering the CRT safe Five volts are supplied at pin for El and also as a clamp for D16 A 3 V logical 1 level is generated across D9 10 11 and 12 through R2 D2 and D3 protect gate A and gate D inputs from exceeding 5 V D1 and D4 prevent the same inputs from becoming negative The two remaining inputs on the W682 are the Z select and Z direct The Z select is a bit that allows the intensity pulse to be multiplexed or time enabled As mentioned before whether or not the intensity pulse is allowed to pass to the output through gate B depends on whether or not a high input is available at pin 13 of gate B This high is continuously available independently of the Z select input when the channel select switch is in the 1 amp 2 position When the channel select switch is in the 1 position intensification occurs only when a high is presented at Z select and an intensify input is presented When the channel select switch is in the 2 position gate B is enabled only when the Z select input is a low The Z direct is an input directly to the grid through C5 Video or other time varying brightness information may be coupled to the grid at
69. ure is the high voltage supply itself Generally all other measurements should be made before considering the high voltage since the majority of no picture conditions will not be caused by the high voltage supply Measuring the high voltage directly is extremely dangerous and not recommended Instead a quick method is to take a long screwdriver and ground the blade with two separate clip leads for safety Turn the VR14 VR17 on for 5 seconds and then SHUT IT OFF After it is off ground out the anode cap on the CRT with the GROUNDED screwdriver If done within 5 to 10 seconds after power is turned off an arc should occur to the screwdriver indicating that the CRT was charged with high voltage If no arc occurs replace the high voltage supply 4 2 2 Faulty Picture a No Focus Check the range of the focus potentiometer on the G838 by monitoring the focus voltage at P4 5 while adjusting the focus potentiometer through its range Minimum range is 350 Vdc to 60 Vdc See G836 for repair Half or Quarter of the Picture Missing Gener ally this condition indicates that one of the two deflection transistors is not working thus only half deflection is available The transistor in question can be identified by observing which side of the screen is not working The left and bottom portions of the screen are controlled by the PNP 2N4399 power transis tors on the deflection heat sink These are the lower two transisto
70. which cause a spark to jump between the anode and other CRT elements The protection circuitry consists of two voltage transient suppressors DEC part no 11 11562 R30 and D13 on W684 R43 G836 R9 on W682 and IK resistor mounted on the CRT socket The resistors act as current limiters diode D13 prevents grid 1 from becoming more positive than OV the voltage transient suppressors mounted on the CRT socket prevent grid 2 and the focus electrode from exceeding 600 V R15 1K 43V RAW 22V D13 014 IN400 IN4001 R11 68 1 2W 10 R8 C1 270uF 15V 10 IN4004 GND BD2 8S2 TIE ETE Pye 43V RAW 22V 015 016 IN4001 IN4001 IN4004 D2 IN752A R16 AL2 43V RAW 22V 0 1 0 1 SW 5w AR2 2N5302 2N5302 BR2 BN2 AE2 BP2 FOCUS 80 80V 7007080 22 R43 BS2 IK 400VDC 62 2w R35 500K R36 R37 Dig 1W 2w 120 c14 IN4004 10 10 zw 10uF D11 D 10 AD2 450V IN4004 1 4004 AJ2 150 VAC x cio cis A GND SENSE 450v t isov zi Bis 4004 150v 25uF K 150 43V 71 RAW 22V 0 4 BK2 SW NOTE SENSE This schematic may not reflect most BE2 recent engineering changes 22V REG BL2 GND SENSE Figure 3 2 6836 Circuit Board AF2 BRIGHTNESS R38 100K 34W 10 76PR C19 25uF 150V CP 0763 Part of the 7007165 Power Regulator Assembly 3 7 6 lt Z SIGNAL J RI 100 6 8 MFD 35V 10
71. y fuse or fan failure thermal cutout The following sequence of events leads to the isolation of the fault s 1 Check fuses If they are in good condition continue If not replace any that are blown and then continue If a blown fuse is replaced leave power on only long enough to complete each check in this procedure 2 Remove all input signals at the rear of the unit and all modules except W682 W684 and G836 3 With a voltmeter or oscilloscope measure the 22 Vdc 20 Vdc to 22 Vdc is acceptable This can be measured between AO1 U red wire and A02 V which is ground Momentarily apply and shut down power If the 22 V is above 22 V the regulator has a fault refer to Appendix A If or below 20 Vdc occurs the 22 V is overloaded continue to the next step 4 Set up to measure 22 V This can be found between 01 blue wire and A02 V which is ground Momentarily apply and shut down power If the 22 V is more negative than 22 Vdc the 22 V regulator has a fault refer to Appendix A If 20 V or more positive the 22 V is overloaded continue to next step Circuit Block Pin 2 02 AO1U AOIK A01P Deflection Heat Sink Pin X A xis Y Axis 5 14 5 15 5 13 5 12 Ps 11 J Wm BWR Regulator Heat Sink Pin P3 1 P3 2 3 P3 12 11 P3 10 7007165 G836 Regulator Circuit Connectors P1 P2 P4 Pi 1 1 3 6 P1

VR14/VR17 CRT display monitor user's manual

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