Ericsson LBI-38505A - Manual (Page 10)

TROUBLESHOOTING PROCEDURES
SQUELCHED UNSQUELCHED
NOISE SQ OUTPUT U605-2
0.2 VDC 9.9V
CAS U605-1
0.1 VDC 9.9V
RX MUTE U605-14
0.2 VDC 9.9V
RUS U605-13
0.2 VDC 4.9V
SQ DISABLE SW. INPUT U606-1
0.2 VDC 9.9V
AUDIO GATE SW. CONTROL U606-11
0.2 VDC 9.9V
If External Decoder is used (CG, DCG, Type 99, etc.), RX Mute will remain low (regardless of noise squelch output), until proper
response is decoded. RX Mute = Noise Sq Output
•
Decoder Output.
In above cases, Sq Disable is assumed high (9.9V). If Sq Disable is grounded, U606-10 = 0.2 Vdc, U606-11 = 9.9 Vdc and Unit
is unsquelched for all conditions.
SQUELCH CHECKS
SYMPTOM PROCEDURE
IMPROPER SQUELCH OPERATION
•
Check voltages on Schematic Diagram.
•
Make gain and waveform checks with noise.
•
Make gain and waveform checks with 6 kHz signal.
•
Check discrete components in the squelch circuit.
•
Replace IC circuit U603.
LOW OR DISTORTED AUDIO
•
Check voltages on Schematic Diagram.
•
Make gain and waveform checks.
•
Check receiver alignment and FM -DET output.
•
Check Q601, Q602, Q605 and other discrete components.
SYMPTOM CHECKS Con’t.
LBI-38505 LBI-38505
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