Ericsson LBI-38505A manual SYMPTOM CHECKS Con’t, Squelch Checks, Troubleshooting Procedures

LBI-38505	TROUBLESHOOTING PROCEDURES		LBI-38505
	SYMPTOM CHECKS Con’t.
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.

SQUELCH CHECKS

		SQUELCHED	UNSQUELCHED
NOISE SQ OUTPUT	U605-2	0.2 VDC	9.9V
CAS	U605-1	0.1 VDC	9.9V
		0.2 VDC	9.9V
RX MUTE	U605-14
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.

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