Best power xstr insulator solution?

[Mr. Land]

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!

 

[N Cook]

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!

I would go for mica plus as little as possible white goo, every time.

 

[Mr. Land]

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!

Ack! I just found the relevant thread. Sorry.

 

[ml]

I would go for mica plus as little as possible white goo, every time.

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

 

[N Cook]

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

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