November 24, 2003 HKLN4216A
10-2 UHF Troubleshooting Tables: Troubleshooting Table for Receiver
No Audio
1. Synthesizer out of lock Verify U201-4 is at 3V dc. Troubleshoot synthesizer/VCO
circuits.
2. Defective IFIC Verify audio is present at U51-8. Check Q70, Y70, U51.
3. RX audio buffer fault Verify audio is present at U451-2. Check U510 and associated
parts.
4. ASFIC fault Verify audio is present at U451-41.
Verify U451-14 is high.
Check squelch setting, PL/DPL
programming. Troubleshoot/
replace U451.
5. Audio PA fault Verify U490-1 is <0.2V dc.
Verify audio is present at U490-5
and 8.
Check Q490.
Check/replace U490.
6. Defective speaker Verify audio is present at speaker
terminals.
If not, check continuity of J471-2
and 3. Check J491. If yes,
replace speaker.
No Receive
(squelch noise
present)
1. No first injection Check that RF level at T42-6 is
approx +6 dBm.
Check that RF level at U251-8 is at
least -8 dBm.
Check injection filter C40-44,
L40-41.
If yes, check Q280 and associ-
ated parts. If no, check U251
and components on pins 5 and
6.
2. No 5R source. Verify U401-49 is high in RX.
Verify Q311 gate is 0V dc in RX
Verify Q311 drain is 5V dc in RX.
Check/replace U401
Check/replace Q313.
Check for shorts, check/replace
Q311.
3. Harmonic filter or
antenna switch fault
Apply on-channel 100 mV RF signal
at antenna port. Verify RF level at jct.
C1/C2 per schematic.
Check TX harmonic filter, D120-
121. Should be 0V dc on D120-
121.
4. Back end fault Apply on-channel 100 mV RF signal
at antenna port. Measure RF levels
from FL51 through U51.
Check components prior to loss-
of-signal point.
5. No second injection Measure RF level at U51-3, verify
approx. 280 mV rms.
If dc voltages at U51-3 and 4
are OK, check Y51 and associ-
ated parts. If not replace U51.
Table 10-1. Troubleshooting Table for Receiver (Continued)
Symptom Possible Causes Procedure Corrective Action
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