Troubleshooting Table For Synthesizer - Motorola Commercial Series Service Information

Troubleshooting Table for Synthesizer

2.0 Troubleshooting Table for Synthesizer
Symptom
Synthesizer Out of 1. VCO fault
Lock (RX mode
only)
2. Synthesizer fault
3. Programming fault
Synthesizer Out of 1. VCO fault
Lock (TX mode
only)
2. Synthesizer fault
3. Programming fault
Synthesizer Out of 1. VCO fault
Lock (RX and TX
modes)
2. Synthesizer fault
3. DC voltage fault
4. Programming fault
Possible Causes Procedure
Verify oscillator is working, check RF
level at U251-10 per schematic.
Check dc voltages at U251 pin 2
Board and IC
through 6 and 10 per
troubleshooting table
.
Verify steering line voltage is
between ~3V and 10V.
Verify TRB line (from U201-2 to
U251-19) is low in RX mode
Verify RX channel programming is
correct.
Verify oscillator is working, check RF
level at U251-10 per schematic.
Check dc voltages at U251 pins
Board and IC
1,3,4,10,15,16 per
troubleshooting table
.
Verify steering line voltage is
between ~3V and 10V.
Verify TRB line (U201-2 to U251-19)
is high (3V) in TX mode
Verify TX channel programming is
correct.
Check that RF level at U251-12 is at
least 150 mV (VHF)
Check that RF level at U201-32 is at
least 150 mV (VHF).
Verify steering line voltage is
between ~3V and 10V.
Verify 4.5V dc at U201-28.
Verify 12.1V dc at U201-47
Verify channel programming is cor-
rect.
Corrective Action
Check VCO tank components
connected to U251-5 and 6.
Check for shorts/opens, replace
U251.
Check D251 and associated
components.
Check for shorts, check U201
Board and IC
voltages per
troubleshooting table
, replace
U201 if incorrect.
Re-program if necessary.
Check VCO tank components
connected to U251-15 and 16.
Check for shorts/opens, replace
U251.
Check D261 and associated
components.
Check for shorts, check U201
Board and IC
voltages per
troubleshooting table
, replace
U201 if incorrect.
Re-program if necessary.
If low/missing, check L276,
C276-7, R276.
If correct, check/replace U201.
If incorrect, check R248 and
C241.
Check loop filter components
R243-5 and C243-5.
Check C231-233, etc., for
shorts. If OK check/replace
U201.
Check for 3V 1.05 MHz sq
waves at U201-14 and 15.
Check C218-228, D220-221.
Re-program if necessary.
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