Re: Salvaged MAC 11B ECU Working OK

[Orin Eman <orin@WOLFENET.com>]

> 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.

That aluminium frame, surprisingly enough isn't grounded, though
once you put the metal box around it, it probably will be.

> Thinking, if the gaskets were the thermoconductive type, then
> my misplacement of the gasket might not explain anything. But
> if the gaskets were electrically insulative, and if the frame is 
> not supposed to be at the same potential as the tab of the 
> transistors, then shorting them to the frame might disrupt the ECU's 
> operation (this could have been one of those experiences that 
> liberated the smoke hidden in a device, but that didn't happen).

A quick test with the ohm meter suggests that the tab on the
transistors is the collector.  These transistors are used
to ground solenoids, eg the wastegate solenoid and the CIS
frequency valve.  Shorting two together would probably have
the effect of turning both solenoids on rather than one.
No surprise that it didn't run will... but not particularly
surprising that none of the smoke escaped!  Those transistors
are mostly on or off and can probably handle plenty more current
than a couple of solenoids!

> Attached bare naked ECU to connector and vacuum, started,
> ran fine, in fact, (and this must surely be my imagination)
> seemed to run a bit better. Boost reached 1.3, same as my 
> original ECU.

Good.  You should run the output tests to make sure everything
clicks and buzzes... did you say you don't have the fuse socket
in the fuel pump relay?  If so, we can work out what to connect
at the computer to start the tests.

Orin.