DIYbanter - View Single Post - Root cause insight into the common BMW blower motor resistorfailures

jim beam

On 03/25/2013 09:40 PM, Bimmer Owner wrote:
On Tue, 26 Mar 2013 04:22:30 +0000, Bimmer Owner wrote:

But, what puzzles me is that nobody has ever mentioned removing
transistors from those two spots. Therefore, I suspect they're just
anchor posts, since the solder is clearly removed in the autopsies.

There is something critical about those two sets of inline posts
because, as I dig deeper, I see others concentrated on them also.

For example, the quote below came with the picture below:
http://www1.picturepush.com/photo/a/...g/12511554.jpg

Quote:

Originally Posted by olivier577

After soldering the lost/refound component,
remaking the joints of the 2 mosfet and testing the FSU alone
with an oscilloscope, here are my observations:
- the FSU works again
- there is no PWM , the gates signals are continuous voltage only ,
this is the reason why it heat so much its aluminium box...
In fact there is no point on the board where square signals are present.
Can somebody check its own FSU if it's the same ?
- the 2 bridges are in fact 2 resistors 10 milliohm used to balance
the currents between the 2 MOSFET and balance the power also.
The mesure of the DC voltage on those resistors can be used to
evaluate the current of the blower and its worn state.
- I guess the principal duty of the computer on the other side is
switching off the power transistors if the control voltage goes under 1V.
I put the FSU back in the car and it still work, I don't know if it will
last long. because of the heat...
Olivier

"sophomoric" indeed.

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fact check required