What happens when MOSFETs burn out?

[TheMonolith2001]

So I have been looking at a couple amps for sale. One of them is another ZR1000 (sure am crazy about these ZRs haha) and the guy said that his speaker wire came out of the sub box (was too short and when box moved it pulled out), hit the casing on the amp, and ran current through it. This supposedly made it get really hot and melted some of the MOSFETs. While at the same time making the amp go into protect. He said it still works it just doesn't put out as much power as it should. I looked up a couple pictures of a ZR1000 opened up and I guess that kind of makes sense? I could see how the MOSFETs could burn up due to heat but wouldn't it just not work at all? Is that even what would happen if the speaker wires contacted the case like that? It seems like if anything the short protection would kick in and it would just keep turning on and off. Maybe burn out the relay. Normally I wouldn't even consider this deal but he is selling it SUPER cheap, and if all it needs is MOSFETs it looks like an easy repair job. A new relay probably isn't a big deal either. I just don't see why it would suddenly put out less power. Those MOSFETs do seem to be the only thing contacting the outer casing though.

As for the other amp, I'll leave that a surprise for now but I should have it tomorrow afternoon, I would have to be crazy to pass it up. It's old school A/B, it's crazy powerful, and its PPI. That's all for now

[hazestorm23]

Its possible they still function but they are bound to burn up anyway . And I wouldn't run it like that anyway. Do your research cost wise and if your able to get it fixed cheap go for it they are decent amps especially if you get them cheap

[Guest]

if the mosfets blew, there is a decent/good chance that other components fucked up too.

[TheMonolith2001]

Well yeah I wasn't going to run it like that. Its more a side project to do for fun and then I'll put it up on the wall or something. I don't have enough electrical for 2 ZR1000s!!!! What other components do you think would be fucked up? As long as it's not so fucked I have to replace every component on the board it might be something fun to do. It's cheap enough that if I got it working and sold it I would make a massive profit too so that is always an option. It's cheap enough that if I just bought it and put it up on the wall and did nothing to it, it would still be cool. His has the silver fins while mine is the black ones. I just thought it would be cool to have one of each. He said once that happened he stopped running it so it's not like it was in that condition running for months....supposedly I guess.

[TheMonolith2001]

Anyone else have any input on what type of damage I might be looking at? I know its pretty hard to guess without looking at it but like I said its cheap.

[justin0943]

idk you might get lucky and spend $40 on new transistor and mosfets and it'll run like new or some of the caps could be gone to which are like a couple buck each if you can pop the top off post a pick let us see what going on,on the inside

[TheMonolith2001]

either way that doesn't sound bad, I'm just going to go for it. I noticed they use thermal paste in there between the mosfets and the outer shell, when I put it back together can I use the same thermal paste I use on CPUs? I probably have a couple tubes of MX-5 or something somewhere already. I'll post pics whenever I get it and then get around to opening it up. Should I just pop the bottom off or should I take it completely apart?

[Casket]

when I put it back together can I use the same thermal paste I use on CPUs?

I always wondered about this as well. I have some AS5 i was going to use on an old amp but i heard since AS5 is conductive , it should not be used.

In for answers....

[TheMonolith2001]

ahhh shit I should know the answer to that question but I can't remember now. I am like 75% sure it is not but that's not really good enough. The reason why I would not use AS5 though is because it takes many heat cycles to set and really start working well. When you overclock computers and you use AS5 you are supposed to way until you have warmed it up and let it cool off at least a couple dozen times before you start overclocking, and then later when it has really set you can usually get a bit more out of it. Anyway what this means is you probably don't want to turn it up loud for at least a month or two if you use that stuff.

[TheMonolith2001]

So I bought the amp. WTF size hex key fits the screws on these things? Is it some weird custom size? I have both a US and Metric allen wrench set and one allen wrench from each ALMOST fits, but none of them turn the screws!!!!