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