LBI-33057
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on these assemblies. The troubleshooting test setup
should be identical to the set-up used in the
ALIGNMENT PROCEDURES section of this manual.
Table 5 lists common problems and most likely problem
areas.
REAR COVER ASSEMBLY
The troubleshooting procedures that follow primarily
assume a problem has been narrowed to a problem on the
RF Board. Transmitter, receiver and synthesizer symp-
toms/causes are outlined.
Transmitter Troubleshooting
Inoperative Or Low Power
Power sources and regulated power supplies should
be one of the first areas to check before troubleshooting
any transmitter problem. The radio's power source,
whether it is a battery or a bench power supply, is espe-
cially critical when troubleshooting a portable radio. Cur-
rent consumption is an excellent troubleshooting tip
when troubleshooting a dead or weak transmitter. See the
Control Board maintenance manual for complete radio
current consumption data.
When the synthesizer is not locked the radio will
beep and flash "NO LOCK" in the display. If the synthe-
sizer does not lock or stay locked at the start of or during
a transmission, I/O Microcontroller will not enable or
continue the transmission. Check LOCK DET at J102/P2
pin 8 for a low or pulsing (not locked) condition. See
Synthesizer Troubleshooting for further details.
1. Check for battery power on l02/P2 pin 2.
2. Check for 5.5 Vdc
±
0.1 Vdc at l02/P2 pin 6 with
the transmitter enabled. Also check the operation
of the TX 5.5V switch to insure 5.5 Vdc is being
delivered to the RF Board at J101/P1 pin 5 when
the PTT button is pressed.
3. Battery power should be present at the Power
Amplifier module pins 2 and 4; if not, suspect Q4
or A1. If current consumption appears normal for
both high and low-power modes, the problem
may be antenna T/R switch DI/D2, the low-pass
filter circuit, or antenna switch SWI. If the low-
pass filter circuit or the antenna switch have a
problem, generally the receiver will also be weak.
A defective pin diode (DI or D2) can cause
transmitter and receiver problems.
4. If low RF power is a symptom, check the opera-
tion of Power Controller AI and Q1. PWR SET
on J101/PI pin 1 should be approximately 1.0
Vdc in low-power mode and 4.0 Vdc in high-
power mode. If Q1 is saturated (collector voltage
is approximately 7.5 Vdc), troubleshoot the PA
for a gain problem. Also check the VCO for low
RF drive. Normal VCO power from A4 pin 1 is 8
dBm.
5. Check Tracking and Channel Data. Reprogram if
necessary.
Excessive Power Output
Short battery life and possible damage to the PA
module may result if a problem occurs in the power con-
trolling circuitry.
1. Check PWR SET from the Control Board. PWR
SET on J101/PI pin 1 should be approximately
1.0 Vdc in low-power (1 Watt) mode and 4.0 Vdc
in high- power (5 Watts) mode. If incorrect,
troubleshoot the D/A converter circuits (in Audio
Processor U8) on the Control Board. Check
Tracking and Channel Data. Reprogram if neces-
sary.
2. The collector of Q1 should be approximately 3.5
Vdc in low-power mode and 5.5 Vdc in high-
power mode. If Q1’s collector stays near 7.5 Vdc
in receive mode, it is most likely shorted. Tempo-
rarily short the emitter and base while monitoring
the collector voltage. If the collector voltage falls,
there is a problem in Power Controller AI.
Frequency Error
If transmit frequency error exists (greater than 2.5
ppm) when the synthesizer is locked, Reference Oscilla-
tor U3 alignment or replacement is necessary. See
ALIGNMENT PROCEDURES for details. The I/O Mi-
crocontroller will not enable a transmission if the syn-
thesizer is not locked.
Modulation Problems
Modulation problems can be caused by a failures in
the audio circuits in the front cover or the modulating
circuitry of the RF Board.
1. Verify modulating audio is present on J102/P2
pin 1. A 1 kHz, 600 mV rms TX MOD signal at
