Motorola EP450 Service Manual page 36

VHF Troubleshooting Tables: Troubleshooting Table for Transmitter
Table 5-3. Troubleshooting Table for Transmitter (Continued)
Symptom Possible Causes
Low Power 1. Low TX injection
2. Low gain in TX stage
3. Incorrect control volt-
age
4. Antenna switch defect
5. Harmonic filter defect
Poor TX range, 1. RF test jack defective
conducted power
OK
2. Antenna matching net-
work fault
3. Defective or wrong
antenna
No internal mic 1. Mic bias fault
audio (EXT MIC
audio OK)
2. Defective mic
3. Defective mic jack
HKLN4216A
Procedure
Check that RF level at jct. R100/
R101 per schematic.
Verify dc voltage at Q100-E is ~1.3 V
(VHF) or ~0.5 V (UHF).
Verify that RF level at U110-1 is
approx. 1 V (VHF) or 1.6 V (UHF).
Verify that the dc voltage at
PWR_SET (R162) is approx 1.8 V
dc (at 1 watt) to 2.6 V dc (at 4-5
watts).
Verify that the dc voltage at U110-2
is approx 2-3 V dc (at 1 watt) to 3-4
V dc (at 4-5 watts). (See schematic.)
Verify dc voltage at jct. R122/L120
(VHF) or R121/L120 (UHF) is approx
1.7 V. Note: Do not attempt to mea-
sure RF or DC voltages at the
diodes. Damage to test equipment
may occur.
Visually inspect components C130-
137, L130-132. Check dc continuity
of L130-132 in RX mode only.
Verify continuity of J140 pins 3 and 4
in RX mode only.
Visually inspect components C140-
141, L140 or L141. Check dc conti-
nuity of L140 or L141in RX mode
only.
Verify correct antenna is installed.
Try another antenna.
Verify U451-35 is low when side PTT
is pressed.
Verify Q470-6 is high when side PTT
button is pressed.
Verify approx 1.8 V dc across car-
tridge when side PTT button is
pressed. Verify audio present (~10
mV rms) when speaking into mic.
Verify continuity between J471 pins
4 and 5.
Corrective Action
Check U251, L291-292, C290-
291.
Verify 5T voltage is correct.
Troubleshoot Q100 circuitry.
Troubleshoot Q100 circuitry.
Check/replace Q100.
Check programming. Trouble-
shoot controller circuitry. Check/
replace U451.
Troubleshoot U150, Q150 and
associated circuitry.
Check/replace D120-121, L120-
121, R120-122, etc.
Repair/replace if necessary.
Replace J140.
Repair/replace if necessary.
Replace antenna.
Check/replace U451.
Check/replace R474, R476, and
Q470.
Check mic connector and R478.
Replace mic cartridge.
Replace J471.
November 24, 2003
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