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im repairing an ampeg svt4 pro and there is an exploded cap and a burnt up power transistor. HMMM i say. i take the preamp board out to have a look at the traces and HOLY SHIT the traces have burned through the solder mask and are sticking up off the board!!!

whatever this guy did, he fucked his shit up royally. pics to follow.

Musta plugged his bass in backwards. People always forget that basses have polarity, and they plug them in the wrong way and damage their amps. This stuff happens all the time.

I'm not sure if my brain is working properly, but how do you plug it in backwards? You just plug one end in the amp and the other in the guitar right?

hes doin it for the lulz.

he slaved an amp into the eq footswitch jack? no idea what the hell he did, but he melted a mosfet, blew a bunch of traces, destroyed some caps, cracked and pwnd some DIPs. this amp is fucked. i dunno what the hell im gonna charge this guy to fix it. gotta find out what the hell he did before i replace anything.

Matt69Volkwagen wrote:I'm not sure if my brain is working properly, but how do you plug it in backwards?

Nah, That was just the first thing that I thought of. It would be a good rumor to start though.

Mewithoutus, I gather you do this for a living? Fix amps that is, not spread rumors.

filtercap wrote:
Mewithoutus, I gather you do this for a living? Fix amps that is, not spread rumors.

yeah i am. im real new to it, but ive been learning alot. its pretty much just gearing up to start designing amps and stuff.

anyhow, heres some pics:

melted traces on the preamp board:



more preamp board:



trace standing off the eq board:





blow'd up MOSFET:





yeah man. looking at the schematic, it looks like he might have slaved an aother amp into the eq footswitch jack. but what the hell. i know thats not what happened. this is gonna be fun

Are you just going to jumper the points together?

Seems like a crappy design when a component fails and the board gets fried. Is the amp fused correctly?

Stangfan wrote:Seems like a crappy design when a component fails and the board gets fried. Is the amp fused correctly?

yeah the power supply is fused. not the power amp. it is a crappy design.

an yeah, im going to point to point wire those broken and fried traces. im hoping the mosfet shorted and pulled too much current that caused all those failures. the circuits that failed are obviously in parallel, because if one of the circuits went out and they were in series, it would have stopped with the first failure.

he TRIED to break this thing.

It's clearly just component failure.

yeah but multiple compnent failure? with multiple circuits between them that werent damaged?

What multiple components? I see a fried mosfet and some messed up PCB traces. One component

I've never really looked into modern amps, but aren't those mosfets part of the power circuit? Certainly they look like they have heatsinks on them.

Mike wrote:What multiple components? I see a fried mosfet and some messed up PCB traces. One component

oh well i didnt show EVERYTHING.

theres a couple of caps that exploded, two quad ic's that cracked in half and melted. all parallel circuits.

oh and some 'sploded driver transistors.

euan wrote:I've never really looked into modern amps, but aren't those mosfets part of the power circuit? Certainly they look like they have heatsinks on them.

yeah those mosfets are in the power amp.