Replacing fets on amp, need recommendations

[xSPLoder 10+ year member]

Need a recommendation on what to use for the white caulk type material used between the fet and the amp casing. I already have the fets just not sure what to use for that material.

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[jasonAz 10+ year member]

look up THERMAL CONDUCTIVE COMPOUND, or thermal grease.

 

[05fronty 5,000+ posts]

op have you repaired amps before? just curious

 

[xSPLoder 10+ year member]

yes, never fets though. mainly loose or broken connections from rca inputs or power and ground inputs. i'm certified in surface mount soldering

 

[xSPLoder 10+ year member]

I majored in electronics and robotics in trade school. I just couldn't remember what that stuff was called and there are a few different kinds you can get for it

 

[05fronty 5,000+ posts]

ok, prob other then just the fets are bad usually

 

[xSPLoder 10+ year member]

yeah I checked them all with my DMM. I am replacing the fets on the whole 1/2 of the board.

 

[xSPLoder 10+ year member]

everything else looks to be in tact so far. that is just the first step though

 

[LBC]

You're going to want some 3m thermally conductive, electrically insulated tape. Those fets need to be electrically isolated from the case or you will pop that amp as soon as the relays kick on. Heatsink compounds can be found that are electrical insulators, however you cannot guarantee that you completely insulate 100% of each fet from the case with this method.

 

[xSPLoder 10+ year member]

I kind of have a feeling that something shorted against the casing but I have examined the board thoroughly and really, those are the only major issues I can find besides some loose capacitors

 

[xSPLoder 10+ year member]

would I be capable of getting all of this at lowes, home depot or radio shack?

 

[xSPLoder 10+ year member]

^^^^^^^^^^^^^^^?
@LBC ; @05fronty ;

 

[Spooney 10+ year member]

would I be capable of getting all of this at lowes, home depot or radio shack?

They won't sell this stuff at home depot or lowes. Radio Shack does sell some heatsink compound last time I checked but it is not the greatest stuff. I wouldn't use it unless it was an emergency. This stuff should be good for what you need:

McMaster-Carr

or this :

ITW Chemtronics Heat Sink Compound | CT40-5 (CT405) | ITW Chemtronics

or this:

Techspray Silicone Heat Sink Compound | 1977-DP (1977DP) | Techspray

This stuff works great as an insulator between the fets and the heatsink:

McMaster-Carr

Make sure you get the .0025 thick tape in whatever width and length you need. Make sure the heatsink is very clean and free of ANY debris or burrs

Also for those loose caps grab yourself a tube of amazing goop or e6000. A little bit of either of these adhesives along the base of those loose caps will secure them to the board and help prevent them from breaking free

 

[stevew007 10+ year member]

yeah I checked them all with my DMM. I am replacing the fets on the whole 1/2 of the board.

dont you want to replace ALL fets in the amp with matched fets from same lot number?

 

[Spooney 10+ year member]

dont you want to replace ALL fets in the amp with matched fets from same lot number?

All fets working together in parallel should have matching date codes for best reliability. Depending on the configuration of the amp you may need to replace all of them to make this happen. Sometimes only half. I myself if I have a failure in the output section I replace all of the outputs just because it makes me feel all warm and fuzzy inside but it is not always necessary. If there is a failure in the power supply though you would want to change them all and match up the date codes. Basically if you are replacing all of a certain part (lets say IRF640) you would want all of the IRF640's to have matching date codes. But when you go to replace the IRF9640's that work with the 640's you won't get matching date codes between the two different part numbers. Again here you would want all of the matching part numbers to have matching date codes so all of your 9640's would need to have matching date codes. Hope that isn't too confusing.