Amp problem: Reverb only works on full

[mr_sooty]

Just got my PV Classic 50 back after a mate, who was going to buy it, decided not to. It's great to have it back actually, It's a fantastic amp and selling it was probably a mistake anyway.

Only thing is, there's a problem it never had before. The Reverb only works when the pot is fully wound up. So I either have all or nothing. Back it off just a smidgen and the Reverb's gone completely.

Is the pot just worn out or something? Could it be that one of the connections to the pot terminals has come loose?

BTW, amp is ten years old and seen it's fair share of use.

Problem is, I have to take the amp apart completely to check, it's got a couple of circuit boards and it's not a very tech friendly design.

Thoughts?

[sumgai]

sooty,


Sorry, but from your description, you've got a bad pot on your hands.

While you're in there getting your hands dirty, be sure to spray clean the other pots, it might help prevent an early repeat experience.

HTH



sumgai

[mr_sooty]

Jul 30, 2009 2:11:43 GMT -5 sumgai said:

sooty,


Sorry, but from your description, you've got a bad pot on your hands.

While you're in there getting your hands dirty, be sure to spray clean the other pots, it might help prevent an early repeat experience.

HTH



sumgai

Sweet, will do. But do you think it could be just a bad connection? Or do you reckon the whole pot needs replacing?

[sumgai]

sooty,

Well, I reckon that the connections to which you refer would be those from the pot to the circuit board, yes? Consider:

If the "hot" terminal (the 'input', if you will) is disconnected, then you have no reverb coming out at all;

If the wiper is disconnected, then you have no reverb coming out at all;

If the remaining terminal (which goes to ground, according to the schematic) is disconnected, then all of the incoming reverb signal will simply move through the pot and out through the wiper. In effect, you'll notice very little change from "full on" to "all the way off".... some reduction of reverb, but even at all the way down, you'll probably experience 90% of full reverb.

So, if you and I are agreed on "connections", then it's a bit obvious that the answer is "No, the connections should not be at issue here", because your symptoms don't match what one or more disconnected connections would show us.

If you were referring to the pot's internal connections, then that's even more work, which I'm sure you're not keen on.


And finally, as discussed in days gone by, use a good grade cleaner on the remaining pots - don't use a tuner cleaner, that has a lubricant in it, which of course attracts dirt all over again. Make sure it's for potentiometers, without any lubricant, and you should be good to go.

I know it's a pain in the tush, but it's the only way to do it right. Good luck!

HTH



sumgai

[mr_sooty]

My cleaner is some kinda CRC contact cleaner, can't remember what model, but it's supposed to be for electronics etc.

Cool, thank for what seems like a sensible diagnosis. Will replace the whole pot, and a few others while I'm at it, and clean the rest.

[mr_sooty]

Replaced pot. All fixed. Cheers.

[sumgai]

sooty,

Ah, nothing like a good winter night's project to warm the soul, right? ;D

Now we need to see about promoting you to Amp Guru around here.



sumgai

[mr_sooty]

Haha, I could do nothing without this forum. At least I don't electrocute myself anymore. Learned that lesson the hard way. Drain filter caps is an important skill I've aquired.

[ChrisK]

Draining filter caps is an important skill I've acquired.

Well, at least now not thru your body.


Someone's always the fuse.................

[sumgai]

"Someone is always the fuse."

I've said that so often lately, the wife is starting to repeat it to others in her conversations. I dunno if that's such a good thing....

[ChrisK]

Yeah, she 'prolly means you......