Peavey Mark III Head Trouble: Looking for Help

[LouDawgBass]

So I picked up a Peavey Mark III Head from a guy off craigslist dirt cheap. Figured something would be wrong with it, but for the first few weeks it sounded great. No issues, awesome. But now I'm starting to run into some problems.

Sometimes when I turned the amp on, it didn't make any sound or just a really low crackling. In order to get it to work most times I had to crank the pre- and post- gain knobs to +6. I was getting concerned I was going to blow my speakers out, but I figured it wasn't that big a deal at the time. Now the sound cuts out while I'm playing...if I can get it to make sound. And so the cycle continues.

I thought it might be the inputs at first, but then I realized it couldn't be that because of the whole cranking the gain knobs deal. Now I'm starting to think it might be gain pots, but I have no idea.

I really need some help here. I've got gigs coming up and I'm short on cash. I have almost enough knowledge to do it myself so I'll give it a go if you know anything.

[WingKL]

Could be anything from a cold solder joint, a bad internal jumper connectors. corrosion in the effects loop connector if it has one, which you can check by bypassing it with a short instrument cable. If you can't afford to send it in to a tech, you'll have to troubleshoot it yourself or get a friend to do it or get a working amp. If you DIY, and can reproduce the problem, try to get a schematic, open it up, and trace the signal with a DMM set to AC or a oscilloscope. If you can't reproduce it on your bench, remove and apply contact cleaner to all internal connectors and examine solder joints to see if they look good and reflow suspect joints.

[J.D.B.]

Try to find something newer. That head is around thirty years old, yes? It's got many aged, deteriorated parts in it (every cap., to mention just a few). I have a couple of them. I had one looked at and the cost to repair it was way above what it cost me, and, really not worth the bench-fee to open it up. Peavey doesn't offer much help on the parts, anymore, either.
Dirt cheap is right. If you really like them, find another, working one.

Josh

[nashvillebill]

First, try putting a jumper across the effects loop send/return (I think this head has a EFX loop). Old amps of all brands have difficulties here, the EFX return is a switching jack and it is very susceptible to oxidation.

Then try cleaning all the pots with Deoxit cleaner (Google if this doesn't make sense).

Actually, Peavey DOES support all their old amps, they are very good about customer support. They will email you a schematic FREE if you call them. They also still have most of the parts you might need (fortunately, Peavey generally used transistors that are also still readily available from Mouser or Digikey).

Old Peavey stuff like that amp is incredibly easy to repair, gotta take issue with JDB on that. Maybe his tech charges too much, but other than a requiring a cap job like every amp more than 30 years old, the Peavey stuff holds up well.

[lesliegl]

Hi ive had a MKIV snce 85 and when it did the cutting in and out thing it was circuit board connector had come loose which is similair to what the other poster mentioned..

Leslie

[BassmanPaul]

Your amp might well need to be vacuumed out. It's amazing how much crud can collect inside one of those.