Peavey XR-600C Troubleshooting No sound

[dadroadie]

Hi To All,
I recently picked up a non-working, well road worn Peavey XR-600C for us to use for our band rehearsals. The problem was no sound output. The person I bought it from said it would not pass a signal but sometimes it would come on if you talked very loudly into the microphone. The power never went off or blew a fuse.
When I got it home I did the input-output jack troubleshooting and found the following.
From main out to main in (everything worked but the graphic EQ section)
From Graphic Out to Power Amp In (everything works including the Graphic EQ section)
Since I can get everything to work when going between the Graphic Out and Power Amp In jacks and reviewing the schematic (attached) I’m thinking that the power supplies are working correctly and there is a good chance that the Power Amp In jack is bad or needs to be resoldered. (Cleaning it with CAIG did not help). There are a couple of input jacks that I think need to be repaired in this matter. Before I open it up is there is anything that I’m missing with this conclusion and should look for? XR600C- XR680C.pdf
Thanks in advance for any suggestions
dadroadieXR600C- XR680C.pdf

[Enzo]

That is the first test you do on an amp like this, plug across the main out to power amp in. Yes, exactly, the cutout contact is dirty or bent on the power amp jack.

This is the most common amp failure there is.

Look up at the top of the menu page for this section (Maintenance and repair) There is a sticky thread: "The dreaded switching jack problem." Read it.


And as a second clue, No sound, but WANG a loud chord through the amp and the sound comes on is further evidence of this jack thing.

The patch jacks like the lower right on your XR600 are a common place for this, but you can also find things like footswitch jacks, and their jacks get dirty and then the amp randomly switches channels on its own, or cuts the reverb or other feature off and on when it feels like it.

Often a spray of Deoxit into the jack works, but you must clean the contact. Also contacts can get damaged. They can get bent, lose their tension, whatever. If the jack doesn't clean right up, just replace it.


Here is my rule of thumb. I measure the resistance of the closed cutout contact. If it is not under half an ohm, it needs service. If you measure say 1 or 2 ohms, it will work right now, but that elevated reading means the contacts are not clean and will cause trouble now and then.

[dadroadie]

Thanks Enzo!
All the Best!
dadroadie