Cause of BMW blower Motor RESISTOR Failure?

[amdx]

Hi Guys,
This is a long thread from sci.electronics.repair, but I think it hit
the wrong audience. I thought you guys might have more incite into
the root cause of this common part failure.

From the OP,

"Does anyone have insight into what is the root cause (and repair) of
the FSU failure that plagues almost every 1997 to 2003 BMW?

http://www.bimmerfest.com/forums/attachment.php?attachmentid=126060&d=1194115994

Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
or by FSU (Final Stage Unit), is known to fry itself in almost every single
E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
http://www.bimmerfest.com/forums/showthread.php?t=143393

The problem with replacing this ~$100 part is that the new replacement FSU
fries itself just as often as the old one did, so you end up repeatedly
replacing your fried FSU every few years or so.
http://www.bimmerfest.com/forums/showthread.php?t=528566

That's fine for most people (although the DIY is a PITA) - but I ask
this newsgroup whether anyone has any insight into WHAT is actually
breaking - and - why?
http://www.bimmerfest.com/forums/showthread.php?t=309399

Here is the best (admittedly sketchy) wiring diagram we have so far:
http://www1.picturepush.com/photo/a/12467819/img/12467819.png"

 

[amdx]

Here in AZ, BMW's are known as the FORD from Europe... Fix Or Repair
Daily.

From your drawing, it looks like blower motor is a classic brushed DC
motor... unlike Mercedes (which I designed which is a 3-phase EC
motor.

I'm guessing a poorly designed PWM control which fails due to
dissipation. (Or even worse, simply a series regulator, hot... hot...
hot.)

Has anyone poked around with an O-scope (on a properly working unit)?

Lots of links (must be a "popular" problem ...

http://www.bavauto.com/se1.asp?dept_id=5260

http://www.bimmerfest.com/forums/showthread.php?t=143393

http://www.ebay.com/itm/BMW-Blower-Final-Stage-Unit-E39-525-528-530-540-M5-2041-/350170462907

http://www.eeuroparts.com/Parts/29072/Blower-Motor-Resistor-Final-Stage-Unit-64116923204G/

http://www.diablo944.co.uk/Hedgehogimageset.pdf

http://blog.bmwpartsforsale.com/bmw-e39-e46-blower-resistor-final-stage-unit-replacement/

http://www.importecwarehouse.com/BMW-Blower-Resistor-Final-Stage-Unit-2000-06-p/bm64116923204.htm

http://www.bimmerwerkz.com/forum/3-series-e46-e90/how-replace-final-stage-resistor-46839.html

...Jim Thompson

Yes Jim,
Just so ya know, I picked up the post from another group because there
was a long thread without a real answer. I thought this group would have
more knowledge, I mean, I'm sure there is more knowledge here
From what I see it is, it is not PWM and not even sure about the linear
regulator. I posted the group in my original post, there is a bit more
about the regulator in the thread. Some thought maybe the motor might be
bad, causing resistor failure, but it is often 3 years after the
resistor replacement.
Mikek

 

[Jamie]

Hi Guys,
This is a long thread from sci.electronics.repair, but I think it hit
the wrong audience. I thought you guys might have more incite into
the root cause of this common part failure.

From the OP,

"Does anyone have insight into what is the root cause (and repair) of
the FSU failure that plagues almost every 1997 to 2003 BMW?

http://www.bimmerfest.com/forums/attachment.php?attachmentid=126060&d=1194115994


Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
or by FSU (Final Stage Unit), is known to fry itself in almost every single
E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
http://www.bimmerfest.com/forums/showthread.php?t=143393

The problem with replacing this ~$100 part is that the new replacement FSU
fries itself just as often as the old one did, so you end up repeatedly
replacing your fried FSU every few years or so.
http://www.bimmerfest.com/forums/showthread.php?t=528566

That's fine for most people (although the DIY is a PITA) - but I ask
this newsgroup whether anyone has any insight into WHAT is actually
breaking - and - why?
http://www.bimmerfest.com/forums/showthread.php?t=309399

Here is the best (admittedly sketchy) wiring diagram we have so far:
http://www1.picturepush.com/photo/a/12467819/img/12467819.png"

THat is a linear controlled speed unit. It has the heat sink sitting
in the path of the air box to help remove the heat. Most likely that unit
fails more when you are using the heater over the air conditioner.

I find it hard to believe that BMW would make such junk like that.

Jamie

 

[miso]

Generally if the module is a resistor, there is one position where the
motor is fed directly. So when the resistor goes open, your only speed
is full blast or off.

If you have more speed values than could be explained by taps in a
resistor, then you have an electronic control of some flavor. Usually
when the electronic control fails, you have no fan at all.

I've replaced these in VWs, Mercedes, and Infiniti. The reality is the
expensive cars have just as shitty fan controls as the cheap cars.

Exar has/had a group that did nothing but reverse engineer the
electronic modules for replacement parts suppliers. You can't believe
the crappy designs used by the manufacturers. It was always a problem if
the replacement parts some use good engineering, or just copy the
moronic designs of the OEM.

I used to think they potted all these modules to protect the circuitry
from the elements, but in reality they were just kind of embarrassed at
the poor engineering in the design.

Most of the time the bipolar designers would spot circuitry that had
potential to damage on start up. As you probably know, breakdown
voltages in bipolar can be a function of pins being floated or shorted
to other pins.

Resistors or electronic controls need heat sinks, so I don't think you
can tell based on the outside of the package.

The replacement part for my Infiniti blower control was a Delphi make in
Mexico! The original part, which looked a bit different (bigger heat
sink) was made in the USA. The Infiniti part isn't potted. I saved it
just to open it up and see if anything smoked. It looks clean. It is a
PCB with 4 semiconductors, one power device, and what looks like a surge
suppressor. The PCB has Picotech on it. It has a 0.004ohm current sense
resistor on. I suppose I can salvage it for yucks. The board is
conformal coated, which makes it hard to read chip numbers.

If I had to fault them on anything, I would say too much heat sink
grease. It is oozed all around the power device. [3 pins, so MOS or BJT].

 

[amdx]

..

Tom

Blame it on Jim, his rates are high.
Mikek

 

[Nico Coesel]

amdx wrote:

[snip]

Yes Jim,
Just so ya know, I picked up the post from another group because there
was a long thread without a real answer. I thought this group would have
more knowledge, I mean, I'm sure there is more knowledge here
From what I see it is, it is not PWM and not even sure about the linear
regulator. I posted the group in my original post, there is a bit more
about the regulator in the thread. Some thought maybe the motor might be
bad, causing resistor failure, but it is often 3 years after the
resistor replacement.
Mikek

All we know is that some component inside a sealed unit seems to have a high
failure rate. It may (or may not) be correlated with motor wear or
impending motor failure.

Some diagnostics need to be done (by the owner of a BMW and some simple test
gear). PWM or not. Condition of motor seizing bearings, arcing commutator,
etc.). And what inside the FSU(?) is failing. Open a bad one up, reverse
engineer it and find out which component is puking.

If this is a common enough failure of a high cost part, I'd consider
designing a better one and marketing it (or a kit) to BMW clubs.

Sounds like a poorly protected implementation of PowerMOS used to
switch in series resistors.

That doesn't need to be the case. The cause can be something simple.
In my car the resistor module has a fuseable link which corrodes and
makes the module fail. Ebay to the rescue...

 

[amdx]

Jim Thompson wrote:

On Tue, 26 Mar 2013 15:28:03 -0700, "Paul Hovnanian P.E."

amdx wrote:

[snip]

Yes Jim,
Just so ya know, I picked up the post from another group because
there
was a long thread without a real answer. I thought this group would
have more knowledge, I mean, I'm sure there is more knowledge here
From what I see it is, it is not PWM and not even sure about the
linear
regulator. I posted the group in my original post, there is a bit more
about the regulator in the thread. Some thought maybe the motor might
be bad, causing resistor failure, but it is often 3 years after the
resistor replacement.
Mikek

All we know is that some component inside a sealed unit seems to have a
high failure rate. It may (or may not) be correlated with motor wear or
impending motor failure.

Some diagnostics need to be done (by the owner of a BMW and some simple
test gear). PWM or not. Condition of motor seizing bearings, arcing
commutator, etc.). And what inside the FSU(?) is failing. Open a bad one
up, reverse
engineer it and find out which component is puking.

If this is a common enough failure of a high cost part, I'd consider
designing a better one and marketing it (or a kit) to BMW clubs.

Sounds like a poorly protected implementation of PowerMOS used to
switch in series resistors.

...Jim Thompson

Could be. Perhaps they need to add a snubber to protect against the dv/dt
transients from the commutator. Particularly in a worn-out motor.

This could be something an enterprising person could put together and sell
as an add-on to the BMW crowd.

Perhaps someone here has a wiring diagram for such a vehicle?

...Jim Thompson

There was one posted earlier in this thread. Unfortunately, the offending
module is just shown as a black box. Not sufficient to understand the
circuit topology.

The original thread had six links from 6 people that had attempted to
remove the potting. All ended in failure.

 

[petrus bitbyter]

On Wed, 27 Mar 2013 10:59:49 -0700, "Paul Hovnanian P.E."

Jim Thompson wrote:

On Tue, 26 Mar 2013 15:28:03 -0700, "Paul Hovnanian P.E."

amdx wrote:

[snip]

Yes Jim,
Just so ya know, I picked up the post from another group because
there
was a long thread without a real answer. I thought this group would
have more knowledge, I mean, I'm sure there is more knowledge here

From what I see it is, it is not PWM and not even sure about the
linear
regulator. I posted the group in my original post, there is a bit
more
about the regulator in the thread. Some thought maybe the motor
might
be bad, causing resistor failure, but it is often 3 years after the
resistor replacement.
Mikek

All we know is that some component inside a sealed unit seems to have
a
high failure rate. It may (or may not) be correlated with motor wear
or
impending motor failure.

Some diagnostics need to be done (by the owner of a BMW and some
simple
test gear). PWM or not. Condition of motor seizing bearings, arcing
commutator, etc.). And what inside the FSU(?) is failing. Open a bad
one
up, reverse
engineer it and find out which component is puking.

If this is a common enough failure of a high cost part, I'd consider
designing a better one and marketing it (or a kit) to BMW clubs.

Sounds like a poorly protected implementation of PowerMOS used to
switch in series resistors.

...Jim Thompson

Could be. Perhaps they need to add a snubber to protect against the
dv/dt
transients from the commutator. Particularly in a worn-out motor.

This could be something an enterprising person could put together and
sell
as an add-on to the BMW crowd.

Perhaps someone here has a wiring diagram for such a vehicle?

...Jim Thompson

There was one posted earlier in this thread. Unfortunately, the offending
module is just shown as a black box. Not sufficient to understand the
circuit topology.

The original thread had six links from 6 people that had attempted to
remove the potting. All ended in failure.

Some of them nevertheless succeeded in removing enough of the potting to
make a repair. It would be interesting to reverse engineer the whole thing.
But someone seems to have done so already as there are second source units
available. Meanwhile, time is running out. These cars from the nineties will
not last much longer I suppose.

petrus bitbyter