6-2 UHF2 Troubleshooting Tables: Troubleshooting Table for Synthesizer (UHF2)
6.2 Troubleshooting Table for Synthesizer (UHF2)
Table 6-2. Troubleshooting Table for Synthesizer (UHF2)
Symptom Possible Causes Procedure Corrective Action
Synthesizer Out of
Lock (No RX
Mode)
1. Defective 12.8 MHz
VCTCXO
Verify clock output FL701 Pin 3 is
12.8 MHz using high impedance
probe.
Repair/Replace FL701
2. 1/2VCC defective Verify FL701 Pin 1, U502-B Pin 5 &
U502–D Pin 14 voltage is 1.9V.
Troubleshoot: 1/2VCC circuitry
3. No RX-Enable Verify U101 Pin 71 (RX-EN1) is high.
Verify Q304 collector voltage is
approximately 4.7 V in RX mode
Check U101 operating
Troubleshoot: Q304 & Q305
circuitry
4. Check PLL-LD port Verify U101 Pin 27 is Low (Normal
Mode)
Verify U101 Pin 27 is swept from low
to high (Power Save Mode)
Troubleshoot: PLL circuitry.
Repair/Replace U701
Synthesizer Out of
Lock (No TX Mode)
1. Defective 12.8 MHz
VCTCXO
Verify clock output FL701 Pin 3 is
12.8 MHz using high impedance
probe.
Repair/Replace FL701
2. 1/2VCC defective Verify FL701 Pin 1, U502-B Pin 5 &
U502-D Pin 14 voltage is 1.9 V.
Troubleshoot: 1/2VCC circuitry
3. No TX-Enable 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 U101 operating
Check U101-Pin 85 is high/
Replace Q407/check LK2 is
short
4. Check PLL-LD port Verify U101 Pin 27 is Low (Normal
Mode)
Verify U101 Pin 27 is swept from low
to high (Power Save Mode)
Troubleshoot: PLL circuitry
Repair/Replace U701
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