Troubleshooting Table For Transmitter (Uhf2); Table 6-3. Troubleshooting Table For Transmitter (Uhf2) - Motorola EP350 Service Manual

UHF2 Troubleshooting Tables: Troubleshooting Table for Transmitter (UHF2)
6.3

Troubleshooting Table for Transmitter (UHF2)

Symptom
No internal Mic 1. Mic dead or defective
audio
2. Mic bias fault
3. Audio Processor IC
not starting up
No EXT. Mic audio 1. J601 defective
2. Audio Processor IC
not starting up
No transmit (No TX 1.PTT switch defective
LED indication)
No transmit (TX 1. Synthesizer out of lock Refer to
LED indication OK)
2. No TX–Enable
Low Power 1. Low TX injection
2. R417 defective
3. Incorrect control
voltage
4. Q403 defective (High
current)
5. Antenna switch defect
6. Harmonic filter
defective
7. Incorrect power tuning
(this has to be performed
only after item 1-6 has
been checked)
Poor TX range 1. Defective or wrong
(Conducted power Antenna.
OK)

Table 6-3. Troubleshooting Table for Transmitter (UHF2)

Possible Causes Procedure
Verify audio present (~10mV rms)
when speaking into Mic.
Check bias of R194 (3.3V).
Verify U101 Pin 78 is 1.1V when
PTT button is pressed.
Verify clock input U102 Pin 14 is
3.5795 MHz using high impedance
probe.
Check connection with EXT mic
Verify clock input U102 Pin 14 is
3.579545 MHz using high
impedance probe.
Verify U101 Pin 44 is low when PTT
is pressed.
Table 6-2
.
Verify U101 Pin 84 (TX–EN1) is high
when PTT is pressed.
Verify Q407 collector voltage is
approximately 4.7V when PTT is
pressed (TX–EN2).
Check the RF level at Q409 & C449
per schematic.
Verify resistance is 0.1 Ohm
Verify Q404 collector voltage is
approximately 5.5V in low frequency
& high power.
Verify U401 Pin 7 is near 0V
Verify CR401 anode voltage is
approximately 1.4V
Visually inspect components
C426 – C429, C445, C446, C430
Check conducted power
Verify correct antenna is installed.
Try using another antenna.
Corrective Action
Replace Mic.
Check/Replace U101
Troubleshoot/Replace FL102
Check/Replace J601
Troubleshoot/Replace FL102
Replace PTT switch PB501
Check U101 operating
Check U101 Pin 85 is high/
Replace Q407/Check LK2 is
short
Troubleshoot Q409 circuitry &
VCO bias
Replace R417.
Troubleshoot APC circuitry
Replace Q404
Replace Q403
Check/replace CR401 & CR301
Repair/Replace if necessary
Re-tune power using tuner.
Replace antenna
6-3