Peavey KB100 popping and thumping with humidity

[Agent24]

Re: Peavey KB100 popping and thumping with humidity

I fixed a friend's subwoofer\amp that was thumping when the cable was moved, at first I thought it was the plug\cable, but it turned out to be broken PCB traces for the jack.

[kc8adu]

Re: Peavey KB100 popping and thumping with humidity

any evil brown glue?

[Marko7]

Re: Peavey KB100 popping and thumping with humidity

Carefully resolder all low-level audio stages, clean the P.C. board in the preamp area, dry it COMPLETELY and then try spraying some clear non-conductive sealent over both sides of the board.
The goal is to make any connections which are in close proximity with each other [in the preamp or output driver I.C. area] from having moisture [beads] conducting spurious D.C. currents around, like between pin 3 (+ In) & 4 (-Vcc) on a dual (or single) op amp I.C. That should help.

[macjedimatt]

Re: Peavey KB100 popping and thumping with humidity

budm, That is the "newer" version of it. I have the 1984 which is slightly different. Hoping to get it apart and post some pictures Tuesday night.

[budm]

Re: Peavey KB100 popping and thumping with humidity

It is solid state amp.
Diagram

[ben7]

Re: Peavey KB100 popping and thumping with humidity

I agree with STJ.

Is this a tube amp?

Also, the extra moisture may be causing a resistor or capacitor to break-down.

Yes, you should do a preventative re-cap of the electrolytics.

[stj]

Re: Peavey KB100 popping and thumping with humidity

when i think of churches - i think of cold damp buildings.

something you probably dont know - flux obsorbs moisture.
make sure it's not got loads of flux all over it.

[SteveNielsen]

Re: Peavey KB100 popping and thumping with humidity

I agree solder joints are certainly suspect. Not just those on the board either. Bad solder joints can hide really well on ground points soldered directly to the chassis.

One very elusive pop, crackle, thump problem I had in a guitar amp wound up being the reverb tank drive transformer that had an intermittent winding short so check that puppy too. You may not be able to measure an intermittent short in it but heating it up when cold and having the noise with a hair dryer could expose it.

Since this is a 90s amp you have it's probably a good idea to replace the electrolytics, or a least check them. I wouldn't worry about the small signal caps. If they are ceramic they could be microphonic but that would present itself differently, with ringing or oscillation at certain frequencies, not pops and thumps.

[macjedimatt]

Re: Peavey KB100 popping and thumping with humidity

Well, it is still at the church. I hope to get it home this weekend and take a look at it myself. The shop that looked at it claims to have already re-soldered a bunch of it. We'll see about that.

I was able to get the schematic and the Peavey parts department has sent me a list of all the capacitors with part numbers and pricing. I doubt I will have to replace all of them. There are about 20 100pF and 0.1uF caps in there. I'm thinking that maybe the power filter caps (2200uF/50V) could be having a problem. But without actually looking at it, this is a big guess.

Being a meteorologist (not on TV!), I understand that humidity does have effects on capacitors and electronics in general. In fact, some instruments depend on this. One thing to note is that it seems to go away after it has been on for an hour or two. My theory is the heat is effectively drying it out. So it could be board damage as well.

Will definitely have to put this under the magnifying glass.

[stj]

Re: Peavey KB100 popping and thumping with humidity

they forgot to ask for foto's

[budm]

Re: Peavey KB100 popping and thumping with humidity

I would also inspect the board real close for any contamination and clean the board real well.

[Sparks88]

Re: Peavey KB100 popping and thumping with humidity

humidity introduces moisture, I would check for dry joints especially in power supply section and output stages, even if the solder looks good I would redo them anyway using original leaded solder.

[macjedimatt]

I have a Peavey KB100 keyboard amp that works great most of the time. However, for the past couple years, when things get humid, it pops and thumps periodically until it warms up. I have taken it to a musicians repair shop at the suggestion of my musical director but they can't find anything wrong with it. I'm wondering if I should just go ahead and re-cap it. Does this sound like something that could be caused by bad caps? It is at least 20 years old so I suppose it is possible that even high quality caps could be wearing out. Any other thoughts?