Finally found a moment to get to testing this out. I discovered that the positive power line into Ch 1 dingo had worked itself loose so there was no connection. I corrected that.
I removed the 4x 99v opamps and didn't see the VU's go back to -20db on power up. Then I encountered a new problem.
Couldn't complete the rest of your test's because I did something to cause the power on the unit to start flickering. All the power connections look to have a good solid connection, the fuse looks good, but now the power and power LED's are flashing on and off at about 1 second intervals. I suspect that I plugged the opamps back in with the power on. With the opamps in, or with the opamps out, the power flickers. Do you suspect I blew something up by plugging those back in while powered up?
Pictures and answers to your questions for the original issue below.
Do you have +24v between 0v and +V on the dingo?
unable to test
Do you have -24v between 0v and -V on the dingo?
unable to test
If you remove the 4 x 99v on the dingos and power up do both VU meters go back to -20dB?
The VU Meters did not return to -20db
Does the 1k trim measure 1k when fully turned down?
unable to test
Send me a photo of the two dingo top without opamps fitted
Dingo_L_Ch.jpg
Dingo_R_Ch.jpg
PCB's look fine. If power supply is hiccuping one or more of the 4 x 24v 1w zeners will be short circuit.
Replace short circuit zeners and you should be going again.
When going again do the above volts test with opamps fitted.
If the meter never turns down even with no input on VU then there will be a power rail down or opamp dead on LA500sc or solder short under the LA500sc pcb.
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