TROUBLESHOOTING GUIDE
Contents
1. Ray Picture Tube The cathode ray tube CRT receives p four inputs e Video R G B MD VOLGE ERU Vertical sweep which scans the CRT EHV POWER SUPPLY SECTION Screen from top to bottom TO VIDEO AMPS RGB FINALS BRIGHTNESS GRID e Horizontal sweep which scans the CRT screen from side to side e High voltage to attract electrons to the CRT screen FOCUS GRID EHV FROM FLYBACK Problems To Look For On The Screen DARK NO RASTER ALSO CHECK HV FLYBACK FUSES THERMISTORS AND VARISTORS HORIZONTAL OUTPUT NO CONTROL OF BRIGHTNESS ALSO CHECK VIDEO SECTION BLANKING MAY NEED TO ION BURNS BE REJUVENATED CHECK VIDEO SECTION CONTROLS2. problem that affects both raster and video a totally black screen for example you will have to perform voltage and continuity checks on all three sections INCIDENTALLY THE MOST COMMON RASTER AND VIDEO PROBLEM is a shorted horizontal output transistor or damper diode The symptom is a black screen with no heater voltage on the CRT and an HV Supply voltage that s ten to twenty volts above normal since the power supply s overcurrent protection circuit has shut off isolating the supply from the rest of the monitor CHECK HERE FOR OQ RASTER PROBLEMS VIDEO PROBLEMS VERTICAL SWEEP SECTION amp HV SUPPLY SECTION HORIZONTAL SWEEP SECTION amp HV 120 160 VDC typical 412KV 25KVDC typical 42 30 VDC typical Extremely High Voltage LV Low Voltage HV High Voltage THE HV SUPPLY SECTION Q4 SERIES PASS REGULATOR Q2 OVERCURRENT SHUTOFF SWITCH AVR X RAY PROTECTION OVP Q3 Q4 INPUT OUTPUT VOLTAGE COMPARATOR CIRCUIT OR IC MODULE Problems To Look For On The Screen DARK NO RASTER COLOR ALSO CHECK HUM BAR DEGAUSS CRT FLYBACK IN PICTURE THEN CHECK VIDEO AMP CHECK ON BOARD SETTINGS ELECTROLYTICS DEGAUSSER HORIZONTAL COIL ABOUT OUTPUT 42 OHMS See Flyback Transformer For LV amp EHV If HV supply voltage rises to 140 150 at TPI check horizontal output damper diode retrace tuning capacitors yoke flyback primary One or more may be
3. E VIDEO AMPLIFIER SECTION NO V SYNC CHECK CAPACITOR IN SERIES WITH WIDTH COIL SEE HORIZONTAL UNSTABLE SWEEP SECTION RC H SYNC MISSING OR CRITICAL TRY SYNC AMP L Blanking luminance AFC Automatic Frequency Control THE VIDEO AMPLIFIER SECTION PREAMPS FROM SYNC Ee SECTION 4 BLACK PREAMPLIFIERS LEVEL INCOMING e VIDEO FROM GAME DRIVERS n POWER AMPS Problems To Look For On The Screen LOW RASTER CONTRAST ONLY HUM BAR IN PICTURE CHECK FILTER CAPS ALL THROUGH MONITOR L Blanking luminance These will be electrolytics of 20 or more MF Most likely the culprit is in the HV section Could also be hiding out around the LV tap of the flyback supplies power to video amps THE VERTICAL SWEEP SECTION V SWEEP FROM SYNC SECTION VERTICAL YOKE About 50 Ohms Problems To Look For On The Screen HORIZONTAL LINE ONLY RED BLUE OR GREEN GHOST IMAGES CONVERGE PICTURE PICTURE IS KEYSTONE SHAPED CHECK VERTICAL YOKE COIL WITH OHMMETER SQUASHED PICTURE OR PICTURE COLLAPSES ODDLY SHAPED RASTER ADJUST YOKE AND CHECK IT WITH OHMMETER THE HORIZONTAL SWEEP SECTION HV SUPPLY SECTION RETRACE TUNING CAP TO amp H SWEEP EHV SUPPLY FROM SYNC SECTION SECTION HORIZONTAL YOKE About 2 5 Ohms Problems To Look For On The Screen DARK SCREEN PICTURE NO BLOOMS RASTE
4. R VERTICAL NARROW ALSO CHECK NO DETAIL LINE ONLY NON LINEAR FLYBACK IN WHITES HV SUPPLY LIGHT COLORS VIDEO AMP SETTINGS 2 PICTURE i Crops RED BLUE OR ODDLY SHAPED GREEN GHOST RASTER IN IMAGES OCCASIONAL RETRACE CONVERGE ADJUST YOKE OVERSCANNING LINES PICTURE AND CHECK IT MAY BE SEVERE CHECK WITH OHMMETER H OUTPUT TRANSISTOR RETRACE TUNING CAPS LV amp EHV POWER SECTION FLYBACK TRANSFORMER FROM HORIZONTAL ANODE SWEEP SECTION HV RECTIFIERS TRIPLER FOCUS BOOSTED HV TO VIDEO G SCREEN BRIGHTNESS FINALS PRIMARY About TO HORIZONTAL AFC ___ About 12 Ohms SYNC SECTION FROM HV o p 5 1 SUPPLY SECTION BOOSTED HV 460 190VDC TYPICAL AFTER HALF WAVE RECTIFICATION Problems To Look For On The Screen REN ie BLOOMS a WHEN TE yl BRIGHTNESS E Yi TURNED UP BLACK SCREEN SNOW HORIZONTAL NO EHV OR NO NO LV STREAKS 6 3V FILAMENT TO SYNC POPPING POWER CRT VIDEO NOISES ALSO CHECK HV CRT VIDEO AMP SETTINGS HORIZONTAL OUTPUT On some monitors an SCR circuit protects against excessive EHV and X ray hazards The SCR shuts down the horizontal oscillator when a hazard exists producing a black screen WARNING DO NOT defeat X ray protection circuitry THE CATHODE RAY TUBE VIDEO FROM VIDEO SECTION VERTICAL SWEEP FROM VERTICAL SWEEP SECTION HORIZONTAL SWEEP FROM HORIZONTAL OUTPUT SECTION The Cathode
5. e e 16 3000 104 November 1982 RASTER MONITOR THEORY amp TROUBLESHOOTING GUIDE Cali TOLL FREE with your monitor problems ELECTRONICS INC 800 621 1253 3401 N California Avenue In Illinois call 800 572 1324 Chicago Illinois 60618 THE RASTER MONITORS WILLIAMS ELECTRONICS USES can be broken down into seven block circuits or sections These are shown in the diagram below A more detailed breakdown of each circuit plus various symptoms that relate to problems in each section follows General Hints FOR TROUBLESHOOTING PURPOSES you should try to mentally localize a problem to one of these seven sections This procedure will save you time and promote an effective step by step troubleshooting method IF A PROBLEM DOESN T SEEM TO SUGGEST A PARTICULAR SECTION try to decide what type of problem it is The diagram below contains an R or a V in each section These initials will help to lead you to a section or group of sections when you ask yourself a single question Does the problem involve picture information or video V or does it involve the illumination of the picture tube or raster R OF COURSE A PROBLEM MAY AFFECT BOTH the video and the raster sections of the monitor Notice the arrows on the diagram Only the EHV amp IV Supply section affects both video and raster But it in turn is driven by the Horizontal Sweep section And the Horizontal Sweep section receives its power from the HV Supply section If your monitor has a
6. shorted Also check AVR output transistor if present This is usually OK Warning Never disable AVR automatic voltage regulator or X ray protection circuits OVP OVER VOLTAGE PROTECTION Some monitors have a separate OVP circuit using a single transistor and an additional fuse At unsafe voltage levels where the risk of X ray emission exists this transistor conducts and shunts the HV power supply voltage to ground through a current limiting resistor With the shunt in place the AVR cuts off and a fuse in the collector circuit of series pass regulator transistor amp 1 blows SOMETIMES THIS FUSE may not blow soon enough to save the OVP transistor If replacement fuses blow test as you would for a black screen but also check the OVP or X ray protection transistor and its circuit ALWAYS REPLACE DEFECTIVE X RAY PROTECTION CIRCUITRY with exact equivalent parts as specified in the monitor manual WARNING Do NOT defeat X ray protection circuitry THE SYNC SECTION USUALLY USUALLY IC IN FROM FLYBACK DISCRETE HI PASS gt Q INCOMING b 16 H SYNC H SWEEP V OSC TO V SWEEP SECTION SYNC INCOMING V SYNC FROM GAME gt V HOO TO VIDEO SECTION Problems To Look For On The Screen 5 gt FULL WIDTH gt RASTER S 22 NARROW ZIG ZAG PICTURE VIDEO OR PIECRUST LOCKS OUT PICTURE OF PHASE A BLANKING PROBLEM HORIZONTAL AFC V OR H CHECK SYNC CHIP ALSO BLANKING AMP SE
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