On 03/21/2013 08:04 AM, Bimmer Owner wrote:
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).

if people priced their time and ignored the damage in which attempts to
unpot invariably result, it's cheaper to just buy a new one.



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?

you don't need it any more than you need the circuit diagram of a chip's
internals - all you need is its function parameters - which you pretty
much already have.

you might be able to pwm the unit itself thus pretty much removing the
heat component thereby prolonging its life [literally] exponentially.


--
fact check required