loud intermittent humming problem

[satwilson]

I have an Ashdown Peacemaker 40. It makes a loud humming sound intermittently, usually preceded by a pop. It does this with nothing plugged in. When I turn down all the controls it stops. When I bring up the master volume control in either channel it comes back, all others still off. I have checked all the tubes with my Sencore tester, no problems there. After reading some other threads here with similar problems, I started poking around on various components on the board and found an area around C-32,C-36,C-68, that when tapped with my wooden spoon, (those caps) produced a popping sound. In addition that area appears to have some leakage from one or more of the caps. These amps tend to run pretty hot. Before I extricate the board from the case I thought I would throw this out to the forum. Amp is about 13 years old. Thanks for any advice, my first post, satwilson

[52 Bill]

Welcome to the place.

...found an area around C-32,C-36,C-68, that when tapped with my wooden spoon, (those caps) produced a popping sound.

I think that you have found the problem. It sounds like you have a broken solder joint on one or more of these caps. I'd pull the board and inspect the trace side for broken solder connections.

[Enzo]

While it is possible your caps leaked, more than one doing it is not very likely. And13 year is not very old for modern caps. Is it possible the leaking you are seeing is really some glue put around the base of the caps to help keep the from shaking? It is quite common to put glue around the base of larger caps on boards.

[satwilson]

Thanks guys for the quick response. Enzo, closer inspection revealed your glue theory. Any caps near tube sockets had melted down glue, some into the tube socket, fouling the contacts, 2-3 contacts in a couple of sockets. Others, physically away from tubes, showed intact glue, Ashdown got a little carried away with the glue thing. I was aware of the glue issues with this amp, but until I pulled the board, seeing the fouled contacts, yeah. I was able to clean the contacts with various xacto blades and hi-tech toothpicks AND 99% isopropyl alcohol. Bill, resoldered all suspect caps. The good, intermittent hum gone, the bad, tapping the caps still pops. ???????

[Chuck H]

The good, intermittent hum gone,

the bad, tapping the caps still pops. ???????

Does tapping the board right there make the same level of pop or is it the caps themselves that seem especially tender? I've seen film caps go slightly microphonic. So little so that I wondered if it wasn't just the sound of me tapping it. Ceramic caps can be much more microphonic. More often I've found that tapping a cap is transferring vibration to the board because it's pretty firmly attached and that the board is transferring vibration to a microphonic tube or another cold solder joint. I'm not saying you don't know what you're listening to. I'm not there. Just relaying my own experience. If it's a ceramic cap you could replace it. As long as the problem is fixed I'd say that if the amp is a head type, and I didn't hear any audible problems, don't trouble with it. If it's a combo amp any microphonic issues are only going to get worse. So if it's positively a microphonic cap, replace it.

[satwilson]

Does tapping the board right there make the same level of pop or is it the caps themselves that seem especially tender? I've seen film caps go slightly microphonic. So little so that I wondered if it wasn't just the sound of me tapping it. Ceramic caps can be much more microphonic. More often I've found that tapping a cap is transferring vibration to the board because it's pretty firmly attached and that the board is transferring vibration to a microphonic tube or another cold solder joint. I'm not saying you don't know what you're listening to. I'm not there. Just relaying my own experience. If it's a ceramic cap you could replace it. As long as the problem is fixed I'd say that if the amp is a head type, and I didn't hear any audible problems, don't trouble with it. If it's a combo amp any microphonic issues are only going to get worse. So if it's positively a microphonic cap, replace it.

Thanks Chuck,
My initial foray at the board, cleaning tube sockets fouled with melted cap glue, suspect cap solders, ended last night very late, still had some popping at cap tap. This AM, based on your suggestions, tapped tubes, caps, board, NOTHING, go figure. Plugged in the "84" Aria ProII RS Knight Warrior and was rockin!!! I do believe the glue contamination in the tube sockets is an ongoing problem. Totally looked for other "solder" probs but did not see any, just taking the board out and tagging everything was reassuring, thanks again everyone.