Session 400 again and again

[Pryde]

So the original thread was getting long and the blown fuse issue was resolved thanks to everyone.

NOW, when the amp is turned on with volume on zero there is super loud and horrible crackle through the speaker, so loud it will blow it if not shut off

OK.
-Triple checked all wiring and solder work (actually the amp was working ok last night but only played it for a minute)
-Still have stable voltages at +/1 51vDC with no blowing fuses
-Getting .04v DC on the speaker jack tip
-Amp is pulling normal with no speaker hooked up (dim bulb) but pulls hard with speaker plugged in (bright bulb)

What now? give up on it?

[soundguruman]

Just because the soldering "looks" OK
does not mean that it is.
Frequently it is better to just re-solder the entire amp.
This is a pretty viable approach to Peaveys. Many have been fixed this way.

You can try narrowing it down by tapping on the circuit boards...trying to localize the bad location.

Also, jacks- preamp out power amp in, can be bypassed with a patch cord.
The switches inside the jacks go bad from oxidization.

[Pryde]

OK found this issue (but likely not the last)

The volume pot had a cold solder joint which compromised it when tightening the shaft bolt. Removed preamp board and re-soldered ALL pots for good measure and finally it is well...for now.

Ever had an amp that turned into your arch-nemesis?

[Jazz P Bass]

.

Ever had an amp that turned into your arch-nemesis?

Maybe one out of twenty.

[Chuck H]

Maybe one out of twenty.

That's not bad! Actually, I don't do repairs for a living so I haven't done the sheer number of repairs that some here have, but I've never had an amp come back. I have, however, found that about half of the repairs I've done involved more work or repair (sometimes A LOT more) than the initial diagnosis revealed.

[Chuck H]

The volume pot had a cold solder joint which compromised it when tightening the shaft bolt.

Many times I've had to FORCE pots or screws that shouldn't have been so tight. Novices commonly think that if tight is good, tighter is better! But to be fair some pots and switches are pretty fragile that way. It's common (for me anyway) to see a design where there is no keyway for stabilizing a pot or switch, the panel is too thick to allow for a lock washer and the part that is available is of mediocre quality @#$%! So you're faced with handing over a repair that will loosen prematurely, attempting to over tighten, and sometimes break the new part or spend way too much time trying to retrofit around the problem. "It" happens.

[soundguruman]

Frequently when you say: "crackling" in a PV amp...
we can pretty much know it's a solder connection.

[Chuck H]

Frequently when you say: "crackling" in a PV amp...
we can pretty much know it's a solder connection.

or a dirty jack switch! (they do love their switching jacks) But yeah, not often anything more sinister.

[Pryde]

Yes the pots are all pcb mounted then bolt to the chassis so I am always careful with those and don't over-tighten them. This one just has a clearly visible pitted, cold joint so it needed a re-flow. Did all other pots for good measure as well.

The pot was allowing intermittent full signal (via pops and crackle) to pass so imagine how loud they were. Gave me a headache figuratively and literally.

[Jazz P Bass]

Of coarse that number will go down if the repairs are all current issue stuff.
SMPS, surface mount, class D.......

[Sowhat]

It's always the last thing you address that is the problem. So... nothing blown or broken, just some mechanical issues. Those will drive you crazy because the first thing you think of naturally is a failed component, that's not always the case however... I didn't think you had any blown parts, just my intuition on that based on the original complaint. The problem description can be of great value most times, and then there's the times that they are worthless and misleading... congratulations!

[Pryde]

It's always the last thing you address that is the problem. So... nothing blown or broken, just some mechanical issues. Those will drive you crazy because the first thing you think of naturally is a failed component, that's not always the case however... I didn't think you had any blown parts, just my intuition on that based on the original complaint. The problem description can be of great value most times, and then there's the times that they are worthless and misleading... congratulations!

Thank you for all your help and encouragement! I can't say enough about the generosity here of folks like you.
You had the right call all along regarding the short to ground via some sort of "jumper". To bad it took me forever to figure it out but another lesson learned, onward and upward