Peavey Century 200 Series

[spartadrive_in]

I checked it and they are good. I think the voltage values that I got are not right with the schematic. Can you look at that schem and tell me what they should be? Just to make sure I looked at the right voltages.

[Enzo]

There are voltage specs all over the schematic, they are all ball park numbers, not critical settings. Like 37v on the output bus. ALl it is is one half the B+ voltage. SO if B+ is 78 or 69 or whatever, the output bus should sit at half that, more or less. And so on, there are plenty of noted voltage points to chose from, compare to the drawings.

But if your problem is intermittent loss of power, it should read right when it works. When it doesn't work is when I expect funny readings. I am comfortable connecting directly to this power amp, but if you are confident your cable from the preamp is OK< then plug a signal into the front, and set it for resoanble loudness out the speaker. Now start flexing the cable, rapping on the front and rear panels, and pushing components on the boards around with an insulated something - a wooden chopstick works great. We are trying to find something that is sensitive and causing your loss of signal.

[spartadrive_in]

pp

[52 Bill]

Good call Enzo.

I haven't seen one of these amps in quite a few years, but I can remember replacing a few of those driver transformers.

I also seem to recall that sometimes if you cut open the paper coil covering, you can sometimes fix internal breaks where the coil winding meets the pc lead wire.

[spartadrive_in]

After hooking up a cd player to it so that I can push down on things I have found that sound DOES come out BUT at a VERY LOW volume. I can hear the music coming through very quiet.
I hope this can tell you what the actual problem area is. I have it open right now and am working on it. THANK YOU!

My guess is that everything is connected but there is a component that is bad. Am I right to think this? Now which one could it be and how do I test?

[spartadrive_in]

After hooking up a cd player to it so that I can push down on things I have found that sound DOES come out BUT at a VERY LOW volume. I can hear the music coming through very quiet.
I hope this can tell you what the actual problem area is. I have it open right now and am working on it. THANK YOU!

[spartadrive_in]

Found It!!

Seems to be the amplifier transistor TIP29C.
When I tap it it works but I have to keep hitting it (with a wooden spoon). I'm going to Fry's today to get a new one and switch it out. This SHOULD be all.

I want to thank you guys for all the help you've given me. I really learned A LOT about amplifiers this time around and best of all I got REALLY acquainted with the layout of my amp. I'll post a pic once I've got her back together.

[Enzo]

If for some reason you have not yet got the new part, a TIP31C is a good sub for that TIP29C. A bit more robust. Nothing wrong with a 29 though.

[spartadrive_in]

Ok here's the pics

Picture of the amp, the guts and the bad transistor.

It's been a week and it still plays good with no problems.
It does get hot though. Is that normal for older amps?

Thanks again!

[Enzo]

Older/schmolder, amps get hot.

There are two largish looking resistors on the power amp board - not hte cement ones, but two that look like carbon comp maybe 2w size? They look brown and discolored. Are they? or is it just the picture makes them look that way? If so, replace them. The transistor you replaced will get warm, that is why it is on a heat sink. Check any resistors associated with it for shifted values.

[spartadrive_in]

I do not see which resistors you are talking about? Could you point them out to me please?

[Enzo]

Immediately under the right-most of the four long cement power resistors is one oriented vertically in the photo. There are two smaller cement resistors between it and the transistor pointed to by the arrow. The second one is immediately to the right of that transistor. It is oriented horizontally in the photo. I guess that second one could be a cap, but I cannot see it clearly.

[52 Bill]

Enzo: I think the resistor on the left is the 22 ohm Zobel network piece, and it does look burnt. The lower right horizontal one looks like a cap to me.

SD: By "it does get hot", do you mean the entire amp? The replacement transistor? Does it get hot while at idle, or after being driven? And how hot are we talking here, warm? Too hot to touch?

[spartadrive_in]

That black on on the right IS a cap. I was thinking of that left resistor. I wondered if it was not supposed to look like that. It does look slightly melted. But I thought maybe it was some chemical they put on it or something. During my troubleshooting before I did replaced it but then I put it back since it was not the problem you know.

Hot while its being driven at high volume. Radiating from the back. When at full blast for a few minutes you can smell a light burning smell.

What is the value of that resistor? I believe it was a 22 ohm if I remember my reading correctly. 1/2 watt?

[Dzavor]

Problem with amp.

Spartadrive_in have you got shematic for power section of this amp?