This Sucks... Kicker Fet's?

[rusty959]

Yea, as boon said I figured I would be replacing the block, but when you say "you'll need to order half a dozen or so to find the couple that match." will I need to be doing something to try to match the fets I buy together to put in the same block?

[Boon]

Look for the date or batch code on the new FETs. Pretty much has to match... if you're lucky you'll get a bunch of identical ones but as mentioned above you may need to buy a dozen or so to get enough matched ones.

One thing to keep in mind when soldering is that the earth mask on the PCBs of these big amps sucks heat like a big heatsink... I hope you have a grunty soldering iron and plenty of wick/a good solder-sucker

Do you have access to an oscilloscope?

Also, if possible, track down a big ass low-ohmage resistor... like 5W or so. Hook it up in series with the amp when you first power it on - that way if there's still a short the amp won't be able to draw enough power to kill itself again (hopefully)

I'll have a look on ampguts later and see if there's anything I can spot to look out for. Any chance of some high-res photos of the amp?

[rusty959]

Alright, ill see what im looking at a bit later. No access to an oscilloscope right now... wish I did.

Ive got plenty of those large 10w 10ohm resistors that I used for doing the power supplies, so I guess they should do the trick. Ill run out in a couple minutes and get some shots of it.

Thanks

[rusty959]

Alright, here are some pics. (clickable thumbnails) I noticed after I got them on the comp my hand must have been a little un-steady, but some are better than others and there are multiple angles. Btw Im not sure if I ever mentioned this before, but I did notice that in the section that had the fet blow, there is a slight separation in the 7 into a 4 and a 3.

Here is what it looks like now that I just got done painting the epic failure my friend turned the outside of it into...

Here you can see the blown fet

Here in a little bit I will take that part of the heatsink off and see if I can get some numbers to look up.

Edited July 8, 2008 by rusty959

[rusty959]

So it turns out when I took of the headsink thing that two of them are actually blown. I guess this doesn't really make a difference though since I was going to replace all 4 anyways. Apparently by the model number at the top, This is what im going to need. So do I only need to replace that one block or do the others too? I went ahead and pulled off the cover and visually checked the others, and they all seem fine. So by what im seeing, the only thing this needs are those fets. I hope thats all.

[Boon]

Your driver circuitry for the affected bit is the section beside the bank of yellow caps. There's 2 ICs in there... give them a REALLY good eyeballing, if you can find a way to test them (resistance check is a really good idea) then do - otherwise as soon as you power it on they're liable to 'hold' the power FETs in a fully 'on' position which will blow them again pretty quickly. Hence the importance of the big ass resistor inline with the power

As you have probably worked out that's in the power supply section. Replace that block of 4 then check the resistance between the power and ground terminals of your amp - it sure as hell shouldn't be 0 but it might not be open circuit either..

Also be careful to check the gate/pulldown resistors - unfortunately with your amp these are the little SMCs beside each FET. Bigger amps have nice big resistors, about the only good thing about them when they pop.....

They often go bad when the FET fails and may not show it outwardly, so check them with a DMM