Table 12 Transmitting Troubleshooting Chart - Motorola Spectra Service Manual

Symptom Possible Cause
No RF power out 1.
2.
3.
4.
5.
No modulation 1.
2.
3.
Distorted modulation 1.
2.
3.
4.
Bad microphone 1.
sensitivity
2.
3.
4.
5.
No/low signalling 1.
(PL,DPL, 2.
trunking, MDC)
Can't set 1.
compensation
2.
Table 12. Transmitting Troubleshooting Chart
TX power level Check TX power level programming (from front panel or programmer).
programming
No keyed 9.6V from Check for keyed 9.6V on pin 15 of J500 w/transmitter keyed. If none, replace
command board command board.
No injection to power a.
amplifier
b.
Power Amplifier Measure PA control voltage (pin 2 of P503); if > 6 volts, replace PA board.
Power control circuit If PA control voltage above was < 6 volts, replace command board.
(on command board)
VCO board a.
b.
HearClear board. Is there > 200mVrms @ pin 19 of P501? If not, replace HearClear board.
Command board If there is the correct voltage @ 19 of P501 and not at pin 11 of J500, check deviation
and compensation programming; if OK, replace command board.
HearClear board a.
b.
Command board Is the output of the command board (pin 11 of J500) distorted? If so, replace command board.
VCO board Replace VCO board.
Compensation not set/ Check compensation setting; if compensation won't adjust, go to "Can't Set Compensation"
working (DPL distorted) below.
Check deviation and Reset if necessary.
compensation
Microphone Speaking loudly into the microphone, monitor the output voltage; if it is not > 1 Vp-p,
replace the microphone.
HearClear board W/80mVrms on the microphone high line, monitor the output of the HearClear board
(pin 19 on P501); if less than 40mV, replace the HearClear board.
Command board W/80mVrms on the mic high line, monitor the VCO mod line (pin 11 on J500); voltage
should be > 200mVrms; if not, replace command board.
VCO board If correct voltage was found on pin 11 of J500, replace the VCO board.
Check programming
Command board Check for proper modulation at pin 11 of J500; if not, replace command board.
Command board a.
b.
RF board If maximum deviation can be set to > 2.5 kHz, but compensation cannot be set,
replace RF board; otherwise, replace VCO board.
Correction or Test (Measurements Taken at Room Temperature)
Check the lock line (pin 14 of J500); if not less than 2 volts, go to synthesizer
troubleshooting chart.
Measure injection; should be > +19dBm; if low, replace VCO board.
All modulation testing should be done w/ the radio keyed & 1Vrms on the microphone
high line of the microphone.
Is there > 300mVrms @ pin 11 of J500? If so, replace VCO board.
These measurements should be made w/ 1 kHz tone @ 80mVrms injected @ the
microphone high line.
Is the output of the HearClear board distorted (pin 19 of P501)? If so, replace the
HearClear board.
All modulation testing should be down w/ the radio keyed & 1Vrms on the mic high
line of the microphone; check that normal voice deviation is OK; otherwise go to
"No modulation" or "Bad microphone sensitivity".
Set deviation & compensation controls to maximum; voltage & pin 17 of J500
should be > 3Vp-p; voltage @ in 11 of J500 should be > 3VP-P; if not , replace
command board.
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