nenett wrote:Plugging a opamp in backwards and powering up will usually kill the opamp or burn one or both the 10R resistors in the same PCB as it.
Check the 2 x 10R carbon resistors still measure 10R each and change the OPA2604AP for a new one should have you going.
Does the meter light up when switching to VU or GR? If not the comp will never switch the bypass relay so will stay in permanent bypass.
Hi Joe. Thanks for the reply. The meter does light up when switching to VU or GR. I checked the resistors and they still measure 10R as before. i'll try and find a new OPA2604AP and change that and then take it from there. Thanks for your help. I'll keep you posted.
Damir[/quote]
You can swap the OPA2604AP from the LA500 PCB and LA500SC PCB to see if the comp behaves differently which will narrow down if it is the opamp or not. Like your comp should pass audio and have makeup gain at the moment and swapping the opamps may stop the audio from working in GR or VU but stop the meter from pinning to the right. Which would show that OPA2604AP is dead.
If you are still having problems send me some well lite in focus photos of the top and bottom of the PCB's to check over.[/quote]
Hi, Joe. i have replaced the OPA2604AP with a completely new one. I ran the power and audio signal through it. The light comes on when I turn the switches to GR or VU on the meter, but it still is pinned to the right. ran some audio signal through it and it comes out unaffected. turning the makeup and threshold pots does not do anything to it. I am including some photos, so you see the PCBs the way they have been built. I can only attach three photos here. Can I send them to your email instead? what's the email?
Damir[/quote]
More photos and answer all questions below.
I need a photo of the underside of the LA500SC PCB and top and bottom of the POT PCB. Always best to send a fully built photo first.
Sounds like the bypass circuit is not working. Which is only the VU/GR switch 1k8 resistor and relay but this travels on the ribbon cable.
Does the meter pin to the right in both VU and GR?
Is the meter back to -20 fully left when VU/GR is off?
Have you got the ribbons plugged in correct positions?
Check you have +16v at pin 8 of the OPA2604AP measured from 0v?
Check you have -16v at pin 4 of the OPA2604AP measured from 0v?