Root cause insight into the common BMW blower motor resistorfailures

On Thu, 21 Mar 2013 09:47:31 -0400, Scott Dorsey wrote:

> I don't see why it is so hard to unpot one of these things and repair them
> directly, especially if it's a semiconductor failure.
> Put a bigger transistor in there.

Here are pictures from the last half dozen who tried that approach:
http://www2.picturepush.com/photo/a/...g/12470740.jpg
http://www4.picturepush.com/photo/a/...g/12470742.jpg
http://www2.picturepush.com/photo/a/...g/12470745.jpg
http://www4.picturepush.com/photo/a/...g/12470747.jpg
http://www5.picturepush.com/photo/a/...g/12470748.jpg
http://www2.picturepush.com/photo/a/...g/12470750.jpg

Most who try to unpot fail, mainly due to damage caused to the
surface-mount circuit board during the initial mechanical degooping
step.

Those deft few who avoid knocking off the surface-mount components
with the debriding chisel, are left with a badly bruised board,
where some have said they've resoldered solder cracks (see pics).

One problem with "put a bigger xtor" is that nobody on this planet
has produced a decent circuit diagram of the FSU.

Does anyone here have access to an FSU circuit diagram?