Peavey XR 8600

[nosaj]

The .22ohm ballasts are

Part Number#30241102

Description .22--5W--5%--WW--AXL

In case anyone stumbles onto this thread and is in the same predicament.

Just a wild shot in the dark but would a shorted or flakey output jack give any of this grief? I keep reading how some of the newer amps are a little intolerant of incorrect speaker loads these days(class d?) So if not set me straight.

nosaj

[Enzo]

This is not a digital amp, no class D, this is a commutating amp, so class G or H, I forget which, and it doesn't matter for the discussion at hand.

These are no less reliable than any other Peavey amplifier or other brand of similar type.

COuld a shorted jack stress the amp? Sure, as it would any amp. So could a bad speaker cord, or a guitar cord used as a speaker cord, or loose jacks in the speaker load. Plugging a cord into the amp with a large static buildup on it can damage a transistor. A good cord pulled halfway out of a speaker jack can short across. Someone could have connected the output of some other amp into this output, and not told anyone of their mistake. Circuits fail all the time for reasons we will never find out. An amp is in the trunk of the car on a frigid day. You bring it in and moisture condenses on the cold surfaces - including the circuit board. You fire up the amp before that evaporates, and BOOM a short circuit. But when you open it up, all that has dried leaving no evidence. You'd never know.

[lowell]

Ok back at it again.

I've got all the 1k resistors from B to E in place.

Replaced an open V103 79L15 (bottom left of PA) feeding Q17 Base.

The inner sets of NPN and PNP all have +/- 660mv Vbe respectively.

Could we say this is fixed and that I can safely install 8 brand new power transistors ?

I'm admittedly nervous about blowing up $25 worth of parts... after having done that once already.

[Enzo]

That is why you use a bulb limiter. And you do not put a load on the amp.

[lowell]

Ok. And other than confirming the 660mv Vbe are there any other readings I should take with the limiter and no load?

[The Dude]

Always confirm that there is no DC on the output before attaching a speaker to a solid state amp.

[lowell]

Ok. When first powered on with limiter, the bulb glows bright for 3 seconds, then goes straight to dim.

There is DC on the output while the bulb is bright. But not once dim. Power transistors Vbe look good. Drivers have:

Vb +/-1.2v
Vbe +/-620mv

Can we say I can power up without the limiter? I'm still concerned about the brightness at power on... but realize it may just be the caps charging.

[Jazz P Bass]

Looks good from where I am sitting.

[lowell]

Ok. Still have it in the limiter. Connecting a speaker I get a loud hum. Still no DC on output...but is 2vAC

ALL gain and master volumes at 0.

[The Dude]

If you have no DC on the ouptut, take it off the limiter and try it. It's being current starved.

[lowell]

Ok what I feared the most. Plugged straight into wall and the DCV on the output immediately climbed from about 0 to 2vDC and I shut it off. I then smelled burning. (Tastes like burning). I'm not sure what to do with this thing at this point.

I should note that I only have 1 PA out of 2 connected to the transformer. Each PA has its own winding and Molex connector.

[nosaj]

Ok what I feared the most. Plugged straight into wall and the DCV on the output immediately climbed from about 0 to 2vDC and I shut it off. I then smelled burning. (Tastes like burning). I'm not sure what to do with this thing at this point.

I should note that I only have 1 PA out of 2 connected to the transformer. Each PA has its own winding and Molex connector.

Your welcome to the 2 you gave me if they will help you out of a jam, you just gotta come out my way.
i still have not had the time to crack them open,
nosaj

[lowell]

Those are both fried too I believe so not sure they'll be of any help. But thanks! Hoping to fix this thang then maybe I can assist on those. Pulling all the transistors out again. Weeeeeeeeeeeee!!!!!

[lowell]

Consensus on no heatsink when using bulb limiter? I'd like to be able to see the components when firing it up. In case I see smoke. The heatsinks cover the PA.

Also consensus on powering up without outer sets of transistors? Only inner transistors installed?

[lowell]

Well I went ahead and tried it. Just inner pairs of devices... with limiter.

So the issue is 2vAC on output. Very low and sounds like 60hz. Don't hear ANY 120hz... Just 60hz.

Thoughts? A filter cap?

EDIT:
Scratch that. My meter says it's 120hz. So I'm thinking filter cap.