TROUBLESHOOTING - E
Contents
1. IN This section will be devoted to providing a better under standing of the Ace Digital Commander system and thus any digital system It is hoped this will be achieved by presenting system integration procedures by indicating how parts of the system might be used with other systems and by presenting troubleshooting procedures for those who have some test equipment System Integration Procedures The individual tune up procedures have been described in detail for the transmitter and receiver and servo neutral set up instructions were provided It would be wise to review those detailed procedures as the integration procedures to follow are studied The use of batteries and switch harness arrangement are largely left up to the builder depending cn his planned system application The following recommendations are in order a It is rather pointless to buy alkaline energizers for the receiver or transmitter packs at around 70 cents per cell when excellent 450 mah nickel cadmium cells which may be re charged hundred of times can be purchased for around 1 50 2 00 per cell from several sources b If alkaline energizers are used three will suffice to provide 4 5 volts for operation of boats and cars c While the builder may take liberty with the power harness for the airborne unit the arrangement shown in Figure J is strongly recommended The switch hook up should also be used for the transmitter A double pole double2. Collector 3 0 Q3 bad or improperly installed T1 secondary open IV Check continuity and value of R9 R10 and R11 Primary of T2 may be open Can also be upset by shorts in AGC line R18 R19 C21 and C20 Servo 1 Check supply voltage 2 Check pot setting approximately 2500 ohms 4 Q4 Emitter 45 Base 1 0 Collector 4 0 and wiper action Q4 bad or improperly installed Check continuity and 3 Check for shorts to board from wires to motor nea R14 R13 and R15 Primary of T3 may 4 Check for p c board shorts 5 Check capacitors placement value and for shorts 5 Q5 Emitter 0 Base 0 4 Collector 4 1 remove from board to check with ohmmeter QS bad or improperly installed D1 shorted or open 6 Check resistors for placement value and continuity T3 primary open Check continuity and value of R16 7 Replace IC 1 R17 Recheck AGC line C22 may be shorted epeeg ca Interference caused by excessive servo motor noise 6 Q6 Emitter 3 8 Base 4 4 Collector 4 5 can be eliminated by installing a 1 mf capacitor Q6 bad check R24 and R25 C24 shorted across the motor terminals orange and white wires 1 Output of Q1 unijunction master clock 2 v em vertical 2 ms em horizontal Absence means Q1 or C1 bed or improperly instaiied Frame rate may be changed by changing value of R3 Increasing gives higher frame rate 2 The differentiated vertical segment from Q1 at Junction of R4 and C2 0 1
3. problems can be localized to some extent by checking the voliage shown in Table i using a VEVM having an input Inpedance of 10 000 ohins per voli oi more However localization is much easier using the scope i Using Parts of the System With Other Sets This system was purposely created to permit its use wiih other systems a The receiver decoder will operate with any transmitter so long as they are on the same frequency and the receiver is tuned to that transmitter This is one of the major applications envisioned If this is the case simply center the servos with the transmitter control and trim centered until the servo output is centered Do not reset the transmitter used be cause that will change the centering of servos for the original system b The builder may wish to use an existing extra servos with the receiver decoder Check if the servos require a positive or negative going pulse and make the PC board modi fication if necessary The MRC five wire servos need 4 8V supplied to both the red and the green wires c The servos may be used with any positive pulse IC decoder system The Heathkit 405 series may require a 10K load between signal and ground d The transmitter is rather limited it will operate a one or two channel receiver system except for the Kraft KP 2B or the Jerobee receiver which do not use the nor mal digital concept and will provide two channels out of de coders designed for more than two ch
4. 1 SN7404 is vad or improperly installed 2v em vertical 2 ms em horizontal 13 Output from second inverter of decoder 1C 1 2 fem vertical 1 ms cm horizontal Absence of signat given the proper signal at output from first inverter means 1C 1 is bad or C3 possibly shorted Available at pin 2 16 Output of fourth inverter of decoder 1C 1 2 v em vertical 1 ms em horizontal Note that this inverter is controlled by the inverter input which was a sawtooth fo NE the output has a sawteoth annearance Ca miay ba ut of tolerance on the low capacitance side tf the input was correct absence of output can be caused only by a bad 1C 1 Available at pin 6 14 Output from third inverter of decoder 1C 1 2v em vertical 1 ms cm horizontal Absence of signal given proper input from second inverter means 1C 1 is bad Avaitable at pin 4 17 Output of fifth inverter of decoder 1C 1 This inverter takes the output from the fourth inverter further squares and inverts it Absence of sianal means and to san s h s iC 17 is wad Output irom fifth inverter is avananie at pin 8 of D 1 SWITCH WIRING TUBING FIGURE 1 15 Input to fourth inverter of decoder 1C 1 Note the integration of pulses from the second inverter coupled via D1 and integrated by C4 0 5 v em vertical 1ms cm horizontal Incovrect signal here could be caused by D1 or C4 bad or incorrectly installed check these fir
5. 5 Q2 bad or incorrectly installed or not being driven prop 4 Output from inverter No 2 Pins 2 and 3 into inverter erly out of pin 3 of IC 3 Check R8 R9 and R11 for No 3 and to diode 4 0 IC 1 bad continuity and C 8 for shorting 5 Output from inverter No 3 Pin 4 0 05 7 Q3 Emitter 6 1 Base 6 5 Collector 0 IC 1 bad C 1 shorted Short to in clock line Q3 bad or improperly installed Q2 not functioning properly Check Ril and R12 for continuity 6 Input to inverter No 4 from diode Pin 5 1 5 IC 1 bad Diode bad 8 Q5 Emitter 1 0 Base 1 7 Collector 6 8 Q5 bad Crystal bad Check continuity of R 15 R 16 7 Output from inverter No 4 to No 5 Pin 6 0 o3 and R 17 IC 1 bad 9 Q6 and Q7 Emitter 0 2 Base 0 02 Collector 6 8 8 Output from inverter No 5 Pin 8 4 0 QG and Q7 bad or iuproperly installed L6 open IC i bad C4 shorted Short in reset line to J of FF 1 9 IC 2 Pin 1 2 3 8 Hl Receiver No Incoming Signal Nickel Cadmium IC 2 bad Power Supply 10 IC 2 Pin 9 1 6 1 Q1 Emitter 1 5 Base 0 7 Collector 2 4 IC 2 bad Q1 bad or improperly installed L1 open Check con tinuity and value of R1 R3 and R4 11 IC 2 Pin 3 4 5 6 10 11 12 0 05 i IC 2 bad 2 Q2 Emitter Q 15 Base 0 6 Collector 3 3 Q2 bad or improperly installed Check continuity and 12 IC 2 Pin 14 4 0 resistance of R6 and R7 T1 primary open 1C 2 bad IC 1 bad 3 Q3 Emitter 0 2 Base 1 0
6. Pin 0 2 0 2 3 2 4 4 0 5 0 2 6 0 7 1 8 3 4 9 0 10 0 11 3 5 12 0 2 13 0 14 3 NOTE Voltage at pin 14 should vary 0 1 v with full elevator stick movement Failure to achieve above voltages for IC 1 and IC 2 are prouauly caused by IC 1 or IC 2 installed improperly or failed C 3 or C 5 may be bad or improperly in cS stalled or C 2 or C 4 may be bad C 6 will not effect Hi Decoder No Incoming Signal Nickel Cadmium IC 1 or IC 2 Power Supply 5 IC 3 Pin 1 0 8 2 0 3 0 4 4 0 5 0 8 6 0 1 Q7 Emitter 0 Base 56 Collector 5 Q7 bad 7 0 8 0 3 9 and 10 0 6 or slightly minus or improperly installed Check value and continuity 11 0 5 12 0 5 13 0 14 0 8 of R20 R21 and R22 C22 and C23 may be short ed these components are on the Receiver board Failure to achieve the readings for IC 3 probably means C1 C2 shorted located on Decoder board IC 3 is failed or a leaky expander is involved in either i case replace IC 3 It is possible but improbable that 2 Input to inverter No 1 Pin 13 IC 1 1 6 C7 or R7 might be at fault The problem of greatest IC 1 bad C1 shorted R1 open Q1 defective concern is that the reading on pin 3 be relatively close or else Q2 will not be controlled properly 3 Output from inverter No 1 Pi 1 into inverter No 2 0 05 IC 1 bad C 1 shorted Diode shorted 6 Q2 Emitter 0 Base 0 2 Coll ctor 6
7. throw switch is used to permit easy addition of an external charger If a charger is to be used the charging plug or jack should be connected to the back or OFF contacts of the switch as indicated Plus from the charger must go to plus on the batteries and minus to minus e The trans mitter will provide quite satisfactory operation from a 9 Volt dry battery such as the Eveready D 6 or Mallory 1603 but don t substitute anything of smaller capacity This size battery will provide about eighteen hours continuous operation However in my opinion the most satisfactory arrange ment is to use a 450 mah 9 6 Volt nickel cadmium pack for the transmitter g Suitable exter al chargers are available from Ace R C Royal Electronics and many electronic stores but be sure they provide the proper charge rate for the cells selected for the system i e 10 of the milliampere hour rating h The transmitter may be operated on just seven nickel cad mium cells 8 4 Volts for car and boat operation i Alter natively if the modeler finds it necessary in order to fly ina high interference area the transmitter may be operated from 10 nickel cadmium cells or eight pencells alkaline for 12 volts However heat sinks should be added to Q6 and Q7 in the transmitcer RF section Assuming at this point that the transmitter receiver de coder and servos have been constructed and the batteries selected the following procedure
8. annels The outputs will not necessarily appear at the first two decoder channels and may appear morc than once depending on decoder design This completes the instructions on the Digital Commander system We truly hope that those who build the set enjoy success with it Further we hope that interest in the material presented here will prompt some of the tinkerers to sit up and generate some ideas for improvement addition or just simply _ new ways of doing things TABLE OF VOLTAGE MEASUREMENTS Taken with 20 000 Ohms volt VTVM DC scale VTVM ground to OV all values in volts If the indicated value is not achieved within about 20 the probable cause is as stated for each measurement voltage values shown in _ Each step presumes voltage checks in preceding steps have been correct All checks assume that boards affected have been checked for shorts solder bridges broken components or Jeads and any leads which may touch others l Transmitter ON 9 v Battery 1 Q4 Base 3 8 Emitter 3 5 Collector 0 Voltage Regulator Emitter must read 3 4 to 3 8 If not Z1 or Q4 is bad or incorrectly installed 2 Q1 Junction R2 Q1 6 8 Junction R3 Q1 4 2 QJ or Cl bad or incorrectly installed 3 IC 1 Pin 1 0 2 0 2 3 2 4 4 0 5 0 2 6 1 8 7 0 8 3 4 9 0 10 0 11 3 5 12 0 13 0 14 3 NOTE Voltage at pin 14 should vary 0 1 v with full rudder stick movement 4 IC 2
9. battery problems a servo or assembly error then it is desirable to have access to a scope for further troubleshooting although a VT VM may be used to check those voltages shown in the Table 1 The accompanying sequcuitial scope trace photos preity well tell the whole story The shape of the proper signal is evident and the amplitude and period are noted The number of pulses shown on your scope will depend on the number of transmitter channels Probable difficulty if the proper waveform is not pre sent is noted The numbered sequence begins with the trans mitter master clock and proceed through the encoder the mod ulator and the RF sections Proper RF output power can be determined with a field strength meter or by demodulating the RF wave and checking it on a scope or VT VM as described in the transmitter instructions Starting with Trace Number 7 the receiver can be checked One trace which is not shown may be checked on a scope hav ing a sensitivity of 0025 volts cm if available that being the local oscillator output which is a simple sine wave The shape of the IF waveform at various stages is very much like that of Trace Number 8 but the amplitude is considerably less so don t fret if it can t be seen on a scope with low sensitivity Faces are not provided for the servos because thev are ra meaningless As indicated earlier problems with servos are almost certainly one of the two things listed For those who do have a scope
10. is used to integrate the sys tem a Tune the transmitter in accordance with the trans mitter instructions If a scope is available set the control pulse widths to precisely 1 5 ms If not set ihe resistance of the control pots at 2500 ohms using an ohmmeter for a close approximation b Connect the receiver and decoder and tune the receiver as described in the instructions with the airborne pack connected to the decoder but no servos If a plastic case is used for the receiver no further tuning is needed c If an oscilloscope is available check the waveforms through out in accordance with the scope traces provided with this article d The servo potentiometers should have been set up in accordance with the servo instructions i e use an ohmmeter to set the resistance at the terminals to which the short blue wires connect to 2500 ohms with servo output centered and blue wires unconnected e If the transmitter pulse widths were set accurately with an oscilloscope ignore the preceding two steps and instead set the servos to exact center by insert ing a small jeweler s screwdriver in the output shaft and adjust ing until centering is correct f Check for smooth linear travel in both directions Having completed the preceding integration the system is ready for installation If a glider or power plane is to be flown a fall range check with transmitter antenna extended should be rn Have a helper walk out with the transm
11. itter with the antenna held upright while slowly and steadily moving one con trol back and forth Caution him not to move the other controls as it is desirable to use their steadiness as an indication of solid operation Hold the model at head level and check operation to a range of around 500 feet Solid operation to this point is an indication of solid operation to an air distance several times greater In Case Of Difficulty In case of difficulty the procedure for this or any system is as follows a Always check battery voltages first thing b Localize the problem determine if the transmitter is radiating and the pulse train is present An audio monitor or an FM receiver may be used for this The audio hum may be heard on an FM set at around 108 MHz When the control stick is moved in either direction the buzz should change tone c If say one servo is dead but one is good swap servos If the servo was bad it won t work on the good channel If the good servo quits then there is a problem with the transmitter engeder or the decoder d Almost any servo problem will t co one of two things a mistake was made in assembly or the iC is bad e If the problem is a servo recheck the assem bly for errors If none is found replace the IC One word of caution reversal of polarity to the servo or shorting the servo output to ground no matter how short the time will ruin the IC f If the problem is not simpie
12. st or 1C 1 is bad Available at pin 5 18 Output of IC2 pins 3 4 5 6 10 11 12 13 if used 2 viem vertical 2 ms cm horizontal The only cause for lack of signal is a bad 1C 2 It is possible for this signa to bo degraded by a failure in a serve a0 ii should be checked both with and without a sorvo plugged in
13. the output of each of the preceding components Exact measurements are possible only with an exactly known input signal level from a signat generator Signal levels for full AGC limiting condition are listed ii Capacitivety coupled autput to decoder 2 v em vertical 1 ms cm horizontal Absence of signal maans C2 is bad or tst inverter in decoder possibly shorted given that output trom Q1 was correct pt h i 3 Output of encoder one shots both took alike available et pin 14 of 1C 1 and 1C 2 Absence means 1C 1 or 1C 2 bad C3 or C5 bad control pots bedly out of proper setting or for 1 2 C4 is bad 2 v em vertical 2 ms cm horizontal The width of the pulse should bo 1 5 ms variable from 1 0 to 2 0 ms via control pot i Ee ME 3 6 RF output from Q6 Q7 0 005 v em vertical 0 02 H sec cm horizontal Visible only on a scope capable of displaying 27 MHz 9 Detected output at collector of QS 1 v em vertical 2ms cm horizontal With AGC full limiting i e transmitter nearby The amplitude at this point shoutd change oniy gradually as transmitter range is changed Abrupt changes are an indication of AGC Instabitity Absence of signal at this point means Q5 is bad provided that IF signal was present through to output of T3 12 Output from first inverter of decoder SN7404 at pin 12 H signal input at pin 12 was correct lin the same as output from C2 absence of signal means decoder IC
14. v cm vertical 2 ms em horizontal Absence means C2 bad 1C 1 Possibly bad or improperly installed Similar waveform present at Junction of C4 R5 and C8 RE6 v 4 Output of expander E3 at junction of R8 and R9 2v cm vertical 0 2 v cm horizontal Absence meens 1C 3 is bad provided the three differentiated spikes Pa at inputs to E1 end E2 respectivety at pins nd 13 vertical 0 4 ms cm horizontal Lightly shaded ares is the 455 KHz envelope Problems here arise from lack of local oscillator operation via failure of Q1 or XTAL improper construction of L2 and L3 L4 or improper operation of Q2 10 Output ot collecice of Q1 on tho decoder 2 v cm vertical i tastom horzontal Shape should be square s shown over futi rocurver range Absence of signa mean either Q1 C22 of C23 is bad or improperty in stalied yivun that the proper ugnali level was present at output from QS 5 Output at collector of Q2 2N3646 2 v em vertical 1 ms cm horizontal Provided that the output from expander E3 was correct absence of signal meens that Q2 is bad or improperly installed Note the shape of the pulse it must not be absolutely square but shaped as shown 8 Typical IF waveform seen at the output of receiver Q4 0 5 v cm vertical 0 4 ms em horizontal Similar waveforms of varying amplitude and sensitive to transmitter range are present at the output from Ti Q3 and T2 Action may be traced by viewing waveform from
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