Re: Salvaged MAC 11B ECU Working OK

[MSV96 <MSV96@aol.com>]

In a message dated 12/18/97 "Douglas Hurst Quebbeman" <dougq@iglou.com>
writes:

<<When I disassembled the ECU last night to consider why it did not
work, I noticed that I'd gotten both of the transparent gaskets
(which go between the aluminum frame/heat sink and the four
large transistor/semiconductor devices) between one set of two
devices, leaving the other set of devices in direct contact with the
frame.>>

<remainder of post snipped>

Yes, those "gaskets" are called heatsink insulators. The tabs of the
transistors are quite likely at a different voltage potential from the
heatsink (heatsinks are typically-but NOT always-at ground potential). Metal
tabs on transistors are usualy the collector which will have voltage present
in most circuit designs. (Be very wary of this if you ever venture into a TV
or 'puter monitor!!!!!)

I'm very surprised that the ECU survived this and it is a testiment to the
design (or the Audi gods were bing nice that day) that it did. Nice work
Hitachi. You were lucky and I'm glad it worked out for you.

Reason I point all this out is for benefit of others who may go there in their
ECU's (or other simular black boxes...car amps for example). I'm sure this is
all very boring stuff for the electronic techie types here but I hope it helps
someone less knowledgeable from potentialy "letting the smoke out" when they
try to fix something they are not fully versed in. While strong on the
electronic side, there are many areas when working on my cars that I may be
over my head knowing "only enough to be dangerous" and I hope clearing this up
may help others.

Mike Veglia
87 5kcstq