Peavey 6505+ 112 Combo Blown Filter Caps

[misterc57]

Bought amp knowing it turns on but no sound. I found one wire at the speaker was disconnected. Looks like the cable was stretched causing one side to slip off. I repositioned the speaker so that would not happen again. After reconnect still no sound.

Pull the chassis to find the big filter caps (C32, C33 and R7) blown. Both output tubes weak, half the preamp tubes weak.

Curious if the damage could have been caused by not having the speaker connected?

I am going to start by checking for voltages. Then replace C32, C33 and R7.

Suggestions appreciated.

MC


Peavey-6505PLUS-112-Schematic.pdf

[J M Fahey]

Absolute zero sound or slight hum/buzz/hiss with your ear to the speaker?
Touch speaker with a battery, does it click?
With amp OFF, unplugged and zero Voltsb remaining in supply, touch a 9V battery at OT primary, from one plate to CT, then from the opposite one, then plate to plate.
Any clicks on the speaker?
Even if weak.

This even before checking voltages or replacing anything.

[xtian]

Wow! Did the fuse(s) survive?

As JM suggests, we want to know if the OT burned up.

[misterc57]

Absolute zero sound or slight hum/buzz/hiss with your ear to the speaker?
Touch speaker with a battery, does it click?
With amp OFF, unplugged and zero Voltsb remaining in supply, touch a 9V battery at OT primary, from one plate to CT, then from the opposite one, then plate to plate.
Any clicks on the speaker?
Even if weak.

This even before checking voltages or replacing anything.

All 3 tests at OT primary produced clicks/crackle to the speaker!

All fuses survived.

The preamp tubes have no voltage on them. Probably because R7 is blown.

So far I will need to order

C32, C33 100uF 550V
R7 390 5W

and perhaps...

VR4 - 31190908 250KB SNGL 12MM HOR. VR4 has a broke shaft.
R102 220K 1W. This one may be okay.

Appreciate the advice and help!

MC

ps. Speaker tested good with a different amp.

[Mick Bailey]

When Peavey finished here in the UK they cleared a lot of unrepaired warranty-returned amps where a new unit had been issued in exchange. At the time I had a fair workload from music shops and studios that had bought these by the pallet load. All of the guitar heads had the same capacitor damage in the same location as per the photos - some had eaten through the tracks and caused additional repair problems. My thought at the time was the caps were defective from new. Interestingly all the PA heads had leaking SMD caps - all in the same locations and confined to certain values. Some were only a few weeks old when I got them.

[misterc57]

Finally got the board and caps C33 C34 off. They were stubborn to remove.

I have a question about removing R7 (390 5W), The legs are on standoffs which appear to be soldered into the board. Do I unsolder the standoffs on the underside of the board to get R7 out? Or is there another way?

C33 topside negative pad came off. Bottom side is okay. Concerns?

Bottom side looks burned at D18 D19 D23 D24 (3rd picture). All diodes test good. Concerns?

All traces in that area underside appear okay and have continuity.

[The Dude]

1) Personally, I wouldn't worry about saving the standoffs. Just solder the new resistor above the board to keep heat away from the board.
2) Topside C33 pad doesn't appear to have a trace connected to it. If that's right, don't worry about it. If there is a trace that's supposed to go to the pad that was removed, you'll have to repair it first.
3) Any burnt area of the PCB near the diodes should be ground out. Burnt board can become conductive. I might just take an exacto knife and cut some grooves in between traces to make sure there's no board conductivity in the circuit. I'd also consider just replacing the diodes even if they check good. They were obviously stressed. It would also be a good opportunity to leave the leads of the diodes longer and get them off the board a bit.
4) Make sure fuses are not only good, but the correct value.

[xtian]

A Dremel with cutoff wheel is a good tool for removing charred FR4. This Mitchell Pro suffered a bad arc between plate and screen. I was worried the board was burned right through, but it was just the surface that was roasted. Amp sounded great when repaired.

[The Dude]

Thanks for posting the picture. Yes, that's what I was talking about- "notching" between traces.

[g1]

I would think the resistor leads should just pull out of the standoffs when you heat them (the standoffs)? Then just suck the solder out. I've never had a problem getting leads out of them.
Otherwise you can just omit them like The Dude said, but the hole left in the board may be a little large.

[misterc57]

I would think the resistor leads should just pull out of the standoffs when you heat them (the standoffs)? Then just suck the solder out. I've never had a problem getting leads out of them.
Otherwise you can just omit them like The Dude said, but the hole left in the board may be a little large.

I did try that but they did not want to come out. Maybe I need to flow some fresh solder into the standoffs first, and try heating and pulling the old resistor legs out again.

[g1]

Maybe I need to flow some fresh solder into the standoffs first, and try heating and pulling the old resistor legs out again.

That should help and that's how I do it. But I don't deal with lead free solder all that much and that would make things a lot more difficult.

[Enzo]

The posts are really just Molex pins. They are made to solder to a board and are staked in place, not just soldered there. SO you can get them out, but not a simple unsolder job.

I usually snip the old part off right at the pin top, then go underneath and heat the solder and pluck out the lead wires, clean out the holes and install a new part. I like the posts as they add support for the part - it vibrates lees and so less likely to break a lead. But I am not married to them, if the post is a problem, I can live without it.

[misterc57]

This project has been put aside for a while. I have not ordered the parts yet.

Anyone know what the voltage is going to C32 and C33? I am wondering if I can use 100uf 500V instead of 100uF 550V caps.

Thank you

[Helmholtz]

This project has been put aside for a while. I have not ordered the parts yet.

Anyone know what the voltage is going to C32 and C33? I an wondering if I can use 100uf 500V instead of 100uF 550V caps.

Thank you

Measure the voltage across C32 in standby.