Marshall 6101 issues - how serious? (complicated question)

[radiohead, lol]

I've got a 1992 Marshall 30th Anniversary 6101 combo amp. It has some issues, but I'm not sure how serious..

let me explain

It was fine for about a week after I got it, but then it started acting weird. (loud crackling etc). It took me a while to figure this out, but I think it's a loose capacitor on the board (it hasn't broken off, but it's pretty loose - I can turn it sideways a little, and if I tilt the chassis, it moves, which is a bit scary).

My question is, is it possible that the circuit board below it broke around where you hook the cap up? I haven't seen any pieces of it, just a bit of solder that broke off...unless something melted. Can I basically just resolder the part back on? I just need to figure out how to disassemble it.

here's what I'm talking about.

http://img89.imageshack.us/img89/9382/dscf0080od2.jpg

See the bias trim pot? It's the upright blue capacitor next to it.

Thanks.

Oh, and I'm aware it looks like a computer :messedup

[Wakarusa]

I doubt the PCB is broken, but it sure sounds like the solder joints on the cap have failed. You should be able to just resolder the component (unless the leads are broken inside the cap).

[John Phillips]

That's a very common problem with large PCB-mount caps - they're heavy enough to crack the joints when they vibrate about. It's quite possible that it did melt some of the solder, since the cracking you heard was an arc between the cap pin and the solder on the board - this is exactly what this fault does sound like, so I'd guess you're dead on about the cause.

It should be a simple matter to resolder it - although getting the board out might not be on this amp ;) - I like to remove all the old solder, bend the pins down onto the PCB to prevent it coming loose (yes I know this is also bad practice in some ways, but it seems to work better in this case) and resolder... and also use some hot-melt glue above the board to stop the cap vibrating.

[radiohead, lol]

Thanks, that helps.

I'm just worried that the board itself got melted/damaged, since the capacitor can turn a little. Shouldn't be too much of a problem to fix if it did, though.

...Unless one of the pins broke off, because I did find this loose piece of wire in there.

Anyway, I'm off to figure out how to possibly take it apart. (no techs around here I'm afraid).

[John Phillips]

Thanks, that helps.

I'm just worried that the board itself got melted/damaged, since the capacitor can turn a little. Shouldn't be too much of a problem to fix if it did, though.

...Unless one of the pins broke off, because I did find this loose piece of wire in there.

Anyway, I'm off to figure out how to possibly take it apart. (no techs around here I'm afraid).
Be patient, and careful. This is NOT an easy amp to work on, as I'm sure you can tell already :). You'll need to cut some zip ties and break the glue on some board connectors, then undo a lot of them, so take notes or more good pics of where everything goes!

If the worst happened and the cap pin broke causing the arc that melted the solder, you'll may have to replace the cap - not a serious difficulty. It's more likely that it just cracked the solder around the pin and then the arc eroded the solder leaving enough space for it to swing about though. Even if the board is damaged, you'll be able to repair it by reconstructing the pad around the pin with a piece of solid wire formed into a loop at the end, and taking it to the next joint on the same trace.

Loose bits of wire (usually cropped component leads that failed to fall cleanly off) are not uncommon in amps, either... though they should be.