Motorola CP150 - Page 47

6880309N62-C June, 2005
VHF Troubleshooting Tables: Troubleshooting Table for Transmitter 6-5
Low Power
1. Low TX injection Check that RF level at jct. R100/
R101 per schematic.
Check U251, L291-292, C290-
291.
2. Low gain in TX stage 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 5T voltage is correct.
Troubleshoot Q100 circuitry.
Troubleshoot Q100 circuitry.
Check/replace Q100.
3. Incorrect control volt-
age
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.)
Check programming. Trouble-
shoot controller circuitry. Check/
replace U451.
Troubleshoot U150, Q150 and
associated circuitry.
4. Antenna switch defect 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.
Check/replace D120-121, L120-
121, R120-122, etc.
5. Harmonic filter defect Visually inspect components C130-
137, L130-132. Check dc continuity
of L130-132 in RX mode only.
Repair/replace if necessary.
Poor TX range,
conducted power
OK
1. RF test jack defective Verify continuity of J140 pins 3 and 4
in RX mode only.
Replace J140.
2. Antenna matching net-
work fault
Visually inspect components C140-
141, L140 or L141. Check dc conti-
nuity of L140 or L141in RX mode
only.
Repair/replace if necessary.
3. Defective or wrong
antenna
Verify correct antenna is installed.
Try another antenna.
Replace antenna.
No internal mic
audio (EXT MIC
audio OK)
1. Mic bias fault Verify U451-35 is low when side PTT
is pressed.
Verify Q470-6 is high when side PTT
button is pressed.
Check/replace U451.
Check/replace R474, R476, and
Q470.
2. Defective mic 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.
Check mic connector and R478.
Replace mic cartridge.
3. Defective mic jack Verify continuity between J471 pins
4 and 5.
Replace J471.
Table 6-3. Troubleshooting Table for Transmitter (Continued)
Symptom Possible Causes Procedure Corrective Action