Troubleshooting Table For Transmitter; Table 5-3. Troubleshooting Table For Transmitter - Motorola EP450 Service Manual

5-4
5.3

Troubleshooting Table for Transmitter

Symptom Possible Causes
No Transmit (no TX 1. PTT switch defective.
LED indication)
2. EXT MIC PTT fault
No Transmit (TX 1. Synthesizer out of lock Refer to
LED indication OK)
2. No TX_ENABLE
3. TX DC switch fault
4. Power control fault
5. No TX injection
6. No 5T source
7. TX gain stage failure
8. Antenna switch failure
November 24, 2003
VHF Troubleshooting Tables: Troubleshooting Table for Transmitter

Table 5-3. Troubleshooting Table for Transmitter

Verify U401-71 goes low when PTT
is pressed.
Verify U401-72 goes low when J471-
4 is grounded.
Table 5-2
Verify U401-50 is high when pin 71
or 72 is low.
Verify Q171-C is 0 V in TX.
Verify Q170-C is at Vbatt in TX.
Check Q150 and U150 dc voltages
per schematic and
Check that RF level at jct. R100/
R101 per schematic.
Verify Q312 gate is 0 V dc in TX
Verify Q312 drain is 5 V dc in TX.
Check RF levels at Q100 and U110
per schematic.
Verify dc voltage at jct. R122/L120 is
approx 1.5 V.
Procedure
Replace PTT switch S441.
Check/replace Q470, L471 etc.
. Refer to
Check/replace U401.
Replace Q171.
Check for shorts, replace Q170.
Repair/replace defective com-
Table 5-4
. ponents
Check U251, L291-292, C290-
291.
Check/replace Q313.
Check for shorts, check/replace
Q312.
Troubleshoot Q100/U110 and
associated circuitry.
Check/replace D120-121, L120-
121, R120-122, etc.
Corrective Action
Table 5-2
.
HKLN4216A