Motorola CP150TM - Manual (Page 170)

June, 2005 6880309N62-C
11-4 UHF Troubleshooting Tables: Troubleshooting Table for Transmitter
11.3 Troubleshooting Table for Transmitter
Table 11-3. Troubleshooting Table for Transmitter
Symptom Possible Causes Procedure Corrective Action
No Transmit (no TX
LED indication) 1. PTT switch defective. Verify U401-71 goes low when PTT
is pressed. Replace PTT switch S441.
2. EXT MIC PTT fault Verify U401-72 goes low when J471-
4 is grounded. Check/replace Q470, L471 etc.
No Transmit (TX
LED indication OK) 1. Synthesizer out of lock Refer to Table 11-2 . Refer to Table 11-2 .
2. No TX_ENABLE Verify U401-50 is high when pin 71
or 72 is low. Check/replace U401.
3. TX DC switch fault Verify Q171-C is 0V in TX.
Verify Q170-C is at Vbatt in TX.
Replace Q171.
Check for shorts, replace Q170.
4. Power control fault Check Q150 and U150 dc voltages
per schematic and
Table 11-4 .
Repair/replace defective com-
ponents
5. No TX injection Check that RF level at jct. R100/
R101 per schematic. Check U251, L291-292, C290-
291.
6. No 5T source Verify Q312 gate is 0V dc in TX
Verify Q312 drain is 5V dc in TX.
Check/replace Q313.
Check for shorts, check/replace
Q312.
7. TX gain stage failure Check RF levels at Q100 and U110
per schematic. Troubleshoot Q100/U110 and
associated circuitry.
8. Antenna switch failure Verify dc voltage at jct. R122/L120 is
approx 1.5V. Check/replace D120-121, L120-
121, R120-122, etc.
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 ~1.3V
(VHF) or ~0.5V (UHF).
Verify that RF level at U110-1 is
approx. 1V (VHF) or 1.6V (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 1.8V dc
(at 1 watt) to 2.6V dc (at 4-5 watts).
Verify that the dc voltage at U110-2
is approx 2-3V dc (at 1 watt) to 3-4V
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
1.7V. 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.