Peavey Special 130 amp issue

[Ford Boswell]

I have a Peavey Special 130 that has suddenly developed a loud screaming hum that cuts out all input sound and goes away if I flip the ground switch. Sometimes it comes back a few minutes later other times it's good for days.

It has the Ken Fox chips and it sounds decent enough and definitely loud enough to handle a live gig. It's a been a pretty consistent amp.

Local tech wants too much to check it and there's no guarantee it will show the problem when I take it in. Any ideas on what the problem "could" be. Things to check, perhaps??

[Larry Dering]

Wiggle the input jack and see if it starts or stops. I repaired a Peavey bass amp with a similar problem and it was the solder cracked at the circuit board on the input jack. Only had to reflow the joint.

[Ford Boswell]

Larry, thanks for the suggestion. I tried that when it first started happening, and again after reading your post...but doing that doesn't cause any hum or crackle. All I can say is that when it first happened I turned the amp off and then tried adjust the volume pots and the hum remained. But when if I flipped the ground switch to either + or - it stopped (and that has been at places where power supply has never been issue, including my home).

I'm not sure where this is coming from but I do agree that it would seem to be a solder crack somewhere.

The upshot is: As handy as this amp is it's pretty inexpensive to buy used. I'm not sure the $65 bench fee to diagnose the issue is worth it when another one can be had for less than $150. That's why I thought I'd take a stab at trying to fix it myself.

[Bill Terry]

Ford, If you're comfortable with poking around on the PCB with the amp powered up, you can remove the chassis and tap around various locations with an insulated 'thing' and usually isolate a cracked solder joint or PCB issue. I've used the butt end of a small screwdriver pretty successfully to solve similar issues on various PCB based amps I've owned.

Some of the other tech gurus may weigh in, but these kinds of things are generally fairly easy to find in my experience.

[Glenn Uhler]

Generally, the voltages in a solid state amp are low, except for the power supply area. But to be on the safe side, I would only go poking around in an amp with a thin wooden dowel, not a screwdriver. Even if you tap with the butt of the driver, you could still bump something "hot" with the blade.

[Larry Dering]

I use chop sticks for the task. the small end comes in handy and they are cheap. I have a Bandit 112 that just started doing the same thing and I found that plugging and unplugging the input jack made it quit. Haven't opened it up yet. The ground switch had the same affect as you described. Will let you know what I find.

[Ford Boswell]

Well i got in there with a dowel and just couldn't pinpoint the issue. I could make the amp hum a few times but it would one area one time and completely different section or component the next. I tried everwhere but couldn't get it to make noise with any regularity. I put it back together and then smacked the top of the amp with my fist a few times and that finally broke whatever was cracked...now I all I get is that awful screeching hum and can't get it to stop regardless of switching things, turning pots. So I guess it's a cold solder. I'll take out the PCB completely now, see what I can find and resolder anything suspicious. Hopefully that will get a little more life out of this amp.

[Larry Dering]

I use a magnifying glass and even then may not see a crack. Sometimes a cold solder joint is only seen with a slight wiggle of the component's and watching the board one at a time. When all else fails I touch the hot iron to each joint for a fraction of a second. Especially at the jack's and control pots. I don't try to reflow every joint. It's better when the area is isolated. Good luck.

[Stephen Cowell]

I use a Sharpie for tap testing.

Next time you get it in failure mode make sure it's the ground switch by giving a good slap to the top of the amp... won't hurt a solid-state amp at all. Any good tech will do this to an amp before sending it out into the world... this is how you test for 'the crunchies'. If it's really the ground switch, just replace (or bypass) it. I'm saying that just flipping the switch might be enough stimulation to cure (for the moment) the bad connection. AFA I know, the ground switch should not affect your amp like this.

AFA reheating connections...

Often it's just easiest to reflow all the connections to the outside world... anything that might get stressed, like jacks, pots, switches, etc. If you use a nice hot iron it doesn't take that long. Have the iron wet before you hit the connection, then feed a little solder after you see the connection thaw. Probably about two seconds per, with a good 40w iron.

If there's any Molex connectors (the white ones) pay special attention there. If this is to be a pro gigging amp I'd consider bypassing all the Molex connectors with wire... they are a common cause of the crunch syndrome. Normalled jacks (pre out/pwr in, vol pedal loop, any loop) are another culprit for crunchy/screamy noises.

[Bruce Derr]

Ditto for any larger parts on the board. Often Peavey would hot-glue large parts such as big capacitors, but the glue can let go over the years and allow the part to vibrate its connections loose.

I like to use an old, um, I mean "vintage" toothbrush for poke-tests.

[Lee Holeman]

What do guys mean by "use the "clean" channel"?