Re: Preventative maintenance time!

Hah Clay, very interesting !

I actually was planning on something similar but I lack any
temperature measuring tools apart from a flue meter ;)

Here's a picture of two transistors removed from an Amplifone board.
The grease is completely crumbled and dried out. So is the mica. The
result is a very poor transition between transistor and heat-sink.

web.jpg

I recently repaired and re-worked an Amplifone deflection board for a
guy in the UK and (as always) I replaced the crumbled and dried grease
and mica's on the power transistors.
I had run the board for quite some time before just to see if I would
notice any heat difference just using my bare hands.
After I replaced the mica's and grease I was able to keep touching the
cooling body WAY longer than before. This already proved what I
thought about this, and what you've proved in a much more scientific
way :D

20 degr. Celsius is an immense difference and about what I would
expected from my earlier experience. And still, the transistor
obviously survived ! ;)

However if you start working on a board, this is something to do with
all cooled transistors and power regulators like 78xx's and 79xx's.

I've got a question though: How much grease do you use ?

I've always tried to get a very even but thin film but when I once put
up a picture Mark Spaeth said it was way too much grease.

Here's some pics of two transistors I put on separate heat-sinks
because the WG6100 was removed from it's frame half-way and I wanted
to get rid of the triangle-shaped side:

Grease applied:
web.jpg

Mica on top and pressed half-way with my thumb so there's an even film:
web.jpg

And the finished result:
web.jpg

Of course I removed the excess grease in the holes etc. And of course
I put another layer on the bottom of the transistor about the same way.

What do you guys think, too thick ? I can't imagine how to get an even
thinner layer. Pics would be great !

And as mentioned, even with this method, the cooling is insanely
better than before.

I only use the regular grease because it's WAAAAAYYY cheaper than the
over-priced "fancy" stuff for case-modders.
The mentioned differences are merely about 1 degree Celsius. Maybe the
ultimate for over-clockers of CPU's, but for this application it's non-
sense.
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Received on Mon Sep 14 10:42:32 2009