[noeqplease]

Hi,

So one of my 4 LA 502 compressors did not work when first turned on. today I tested all the items on your handy troubleshooting list.

1. Checked for bad / cold solder joints, did not find any visible ones. Tested some different places on the circuit, and was able to get readings everywhere pretty much.
All ICs, transistors, and capacitors are in their correct orientations. No leads are near the chassis plate at all.

2. Checked DC voltages: + voltage is 16.14VDC, - voltage is -16.60 VDC. On TP1 I do get 1.105 VDC with the circuit bypassed, 1.04 VDC with the circuit engaged. So, there is some issue.

3. Applied a 1 VAC 1kHz signal to the input to follow it: Black probe on 0 V point.
R2 right leg reported 0.69 VAC
R 5 Right leg reported 0.025VAC with circuit in bypass, 0 VAC when engaged. REV 1.4
TP1 Reported 0 VAC, and no change when turning the GAIN knob.

So, something is definitely up. Please let me know what else I should test and how, so I can pinpoint the issue.

Thanks!!!

PS the other 3 compressors work beautifully.

[noeqplease]

Just tested all 6 OPA 2134 ICs, all passed the test, both amps on each IC.

Will continue testing...

[noeqplease]

pic of the OPA2134 tests...

[JPK]

Remove U1 and check again R5 right pin.
You can keep U1 removed until this is fixed.
Check the value of R5. It will be lower than 100k because of the other components around.
Checl the optocoupler is in the right direction.
Look for solder bridges or bad joints around R2, R3, R4 and the ratio switch.