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Best power xstr insulator solution?

I picked up an as-is JVC receiver to play with on eBay recently. From what I've read, this particular model is renowned for running extremely hot. Removing the top cover revealed that this is actually the case: the plastic outer sleeves of all four of the large power supply filter caps have all shrunk, and one of the four caps actually burst open at the top (spraying a lot of paper debris inside.)

This unit has 7 power amplifier circuits utilizing 14 power MOSFETS. All of the output MOSFETs are mounted to one long, flat heatsink, with one long flat clamp bar.

Since I've gone through the trouble of getting out the main board to replace the caps and test related stuff in the power supply, I decided to check all the output MOSFETs too.

The output MOSFETs were insulated from the heatsink by what I'm guessing are rectangular sheets of silicone rubber, with groups of 4 devices sharing a single sheet, with the final 2 on a smaller sheet (the JVC service manual calls them "RUBBER COOLERS", but let's not go there.) When I removed the devices, the sheets pretty much disintegrated (perhaps due to heat/age). Now I'll need to replace them all.

Being an old-timer I'm used to using the thin mica insulators w/ the white thermal compound. But this approach would be considerably less thick than the original silicone sheets. Are the silicone sheets superior or inferior to the mica/paste approach? (I vaguely remember seeing a thread about this, but I couldn't seem to find it.)

I looked on my favorite parts sites (Digikey, Mouser, Newark) - none seemed to have anything like these.

Should I try to get original parts, or...?

Thanks!

Reply to
Mr. Land
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I would go for mica plus as little as possible white goo, every time.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

Ack! I just found the relevant thread. Sorry.

Reply to
Mr. Land

hi

typically the rubber like sheets are better than other solutions the latest i've seen is to place a foam rubber like sponge over the entire top (component side( of a ckt board then place a heat sink metal fin on top which had some really amazing overall cooling

it's hard to imigane how a rubber material can do it, but don't think of it as a rubber sheet think of it as conductive material, screwing it down forces the softer material to cover more

not really expert on this just what i read

Reply to
ml

Don't be misled by manufacturer's blurb

This is my experience of a like for like replacement

Kustom KPM6160A mixer amp from 1997 The silicome rubber heatsink insulating pads had shrunk, probably excessive heat but otherwise no malfunctionm there was connector problems elsewhere. Replaced with mica washers. Previously took 50 minutes to stabilise at 33 deg C above ambient pumping 9Vac of 400Hz continuous sine into 4 ohms. With mica, down to 30 minutes to stabilise at the same temperature and you could keep your fingers on the body of the trannies, too hot previously.

The pads may have chemically failed , but even then , mica does not degrade

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

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