Troubleshooting Table For Synthesizer (Uhf2); Table 6-2. Troubleshooting Table For Synthesizer (Uhf2) - Motorola EP350 Service Manual

6-2
6.2

Troubleshooting Table for Synthesizer (UHF2)

Symptom
Synthesizer Out of 1. Defective 12.8 MHz
Lock (No RX VCTCXO
Mode)
2. 1/2VCC defective
3. No RX–Enable
4. Check PLL–LD port
Synthesizer Out of 1. Defective 12.8 MHz
Lock (No TX Mode) VCTCXO
2. 1/2VCC defective
3. No TX–Enable
4. Check PLL–LD port
UHF2 Troubleshooting Tables: Troubleshooting Table for Synthesizer (UHF2)

Table 6-2. Troubleshooting Table for Synthesizer (UHF2)

Possible Causes Procedure
Verify clock output FL701 Pin 3 is
12.8 MHz using high impedance
probe.
Verify FL701 Pin 1, U502–B Pin 5 &
U502–D Pin 14 voltage is 1.9V.
Verify U101 Pin 71 (RX–EN1) is
high.
Verify Q304 collector voltage is
approximately 4.7V in RX mode
Verify U101 Pin 27 is Low (Normal
Mode)
Verify U101 Pin 27 is swept from low
to high (Power Save Mode)
Verify clock output FL701 Pin 3 is
12.8 MHz using high impedance
probe.
Verify FL701 Pin 1, U502–B Pin 5 &
U502–D Pin 14 voltage is 1.9V.
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).
Verify U101 Pin 27 is Low (Normal
Mode)
Verify U101 Pin 27 is swept from low
to high (Power Save Mode)
Corrective Action
Repair/Replace FL701
Troubleshoot: 1/2VCC circuitry
Check U101 operating
Troubleshoot: Q304 & Q305
circuitry
Troubleshoot: PLL circuitry.
Repair/Replace U701
Repair/Replace FL701
Troubleshoot: 1/2VCC circuitry
Check U101 operating
Check U101–Pin 85 is high/
Replace Q407/check LK2 is
short
Troubleshoot: PLL circuitry
Repair/Replace U701