Motorola Commercial Series Service Information page 21

Troubleshooting Table for Transmitter
Symptom
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
No EXT MIC audio 1. Mic bias fault
2. Audio path fault
3. Defective audio
accessory
Possible Causes Procedure
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 L141 in 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 1.8V dc across
cartridge when side PTT button is
pressed. Verify audio present (~10
mV rms) when speaking into mic.
Verify continuity between J471 pins
4 and 5.
Verify approx 1.8V dc across EXT
MIC cartridge in TX mode. Verify
audio present (~10 mV rms) when
speaking into mic.
Verify mic audio present (~10 mV
rms) at U451-46.
Verify amplified mic audio present
(~200 mV rms) at U451-40.
Try another accessory.
Corrective Action
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.
Check Q470. R475, R477,
L471. Check VR473, VR475,
D470 for shorts.
Check L471, C470.
Check/replace U451.
Replace defective accessory.
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