Peavey Supreme

[goldtop5]

I've got a peavey supreme solid state guitar head that's producing -15vdc on the input jack (tip). I'm trying to trace it down its source but cannot find the fault. Any hints?

[The Dude]

Please post a schematic if you have one. "Semi-guessing" a shorted 1n4148 near the input circuit? Check diodes.

[goldtop5]

I replaced the diodes (d3 and d8) and the problem still persists. I'm also reading the -15vdc on ground of the input circuit.

[Jazz P Bass]

If you are truly measuring -15Vdc on the input jack, then you have a missing connection to ground.
The schematic shows two connections.
One to chassis ground & one to circuit ground.
So you have either a bad solder joint at the jack or copper traces are blown.

What are you using as your ground reference?

[goldtop5]

I've been using the chassis as ground reference. There is also -15vdc measured at the ground of the input jack.

[Jazz P Bass]

It appears that you have a broken ground trace at the jack.

[goldtop5]

I will check that out. If there is no resolution, then I'll check with the customer to see if he would like to have the preamp board replaced...that is if one is available. Part of me wants to throw this thing in the trash, along with all the behringer crap. Or better yet, since our workshop is out in the country, we have burn piles!

[nashvillebill]

Why would the entire preamp board need replacing?

[goldtop5]

Couldn't tell you, nash. But sometimes extreme cases may call for extreme measures.

[nashvillebill]

It's a very simple transistor circuit, so it's hard to imagine this being an extreme case. If your car has a problem with a spark plug, do we automatically assume we need to replace the engine?

Could be a bad ground as Jazz suggests. What are the voltages to ground from each leg of C31 to chassis ground?

[DrGonz78]

I will check that out. If there is no resolution, then I'll check with the customer to see if he would like to have the preamp board replaced...that is if one is available. Part of me wants to throw this thing in the trash, along with all the behringer crap. Or better yet, since our workshop is out in the country, we have burn piles!

Is the thing chaulk full of surface mounted components? We all at one time have felt this type of frustration and it feels really good later fixing the amp.

[goldtop5]

I believe it may have been the same voltage on both sides. I don't have the amp on the bench yet, but I will check it again tomorrow just to be sure.

[goldtop5]

No surface mounts, thank goodness.

[Jazz P Bass]

Please run a continuity check from chassis ground to the input jack ground.