Root cause insight into the common BMW blower motor resistorfailures

[Bimmer Owner]

All those photos only show one side. I full reverse engineering
should be done to draw a full schematic but I've never had my hands on
that module. It would probably take a couple of them, because ot the
potting.

These photos show both sides.
http://www.bimmerfest.com/forums/showthread.php?t=309399

Nothing was removed, so I can't figure out WHAT you guys are
saying is the transistor removed.

Can you circle one of these pictures to show WHERE you think
something was removed?

http://www.bimmerfest.com/forums/attachment.php?attachmentid=367580&d=1363957253
http://www.bimmerfest.com/forums/attachment.php?attachmentid=363800&stc=1&d=1361831815
http://www.bimmerfest.com/forums/attachment.php?attachmentid=363808&stc=1&d=1361837887

 

[Bimmer Owner]

If it's just a typical DC motor with two leads, apply 12V and
it should run full speed. You could [then] measure how many amps
it draws when running.

That makes a lot of sense!

Plus, it's easier to hook up leads to the harness connector than it
is to get a DMM lead on the impossibly hard-to-get-to 40Amp Fuse F76 for
the blower motor.

 

[Bimmer Owner]

Have you got a link to these "common problems" you keep posting about?

Of course. Nothing I've ever written is not well documented.

I'm not sure "which" common problem you're asking about, so, here is
just a sample of the most-common problems that afflict almost every
BMW E39, E38, and E46 (I'm sure there are others but I'm only familiar
with those models that use the M54 engine).

http://www.bimmerfest.com/forums/showpost.php?p=6097104&postcount=46

Behr cooling system leaking
Plastic DISA valve breaking & destroying the engine
Cluster pixel tape lifting
MID pixel tape lifting
Hella PBT headlight adjusters breaking
Power steering cap & hose leaking
Trunk wiring loom fraying
CCV clogging
Bosch ABS control module frying
Cupholders breaking
I6 VANOS seals deteriorating
V8 valley pan gaskets leaking
GKR/BMW/Valeo FSU/FSR dying
Thrust arm bushings leaking
Ambient temperature sensor breaking
Window regulators breaking
Vapor barrier adhesive leaking
Jack pads falling off
Windshield cover molding crumbling
Driver's seat control switch breaking
Rear center brakelight socket melting
Seat cables fall out causing seat twist
Windshield washer tanks & pumps leaking
BMW roundel paint chipping
Vent trim corner cracking & wood trim varnish cracking
Rear center brake light socket melting

Note: The reference above has detailed links to EACH of these topics above.

 

[Bimmer Owner]

serious question - why did you buy it?

As for me, I fell sway to all the people saying how great the bimmer was.

It was only after I owned it, that I realized that BMW engineers knew
how to design a suspension and a drive train, but they had no idea
how to build a machine.

To their credit, some people say it's not the engineers fault as
they probably know by now that every single Bosch 5.7 ABS control
module fried in every one of the vehicles it was placed in, and that
the final stage unit cooked itself to death in every single BMW it
was ever placed in, and that the 2-bar plastic cooling system
sprang a leak on almost every single BMW ever built, etc.

In fact, there's absolutely NO WAY BMW can't know about these
egregious engineering flaws. So, the common conclusion is that
their customers don't care - so why should they.

To me, it smacks of 3rd-grade engineering from BMW, so, that's why
I, for one, am amazed (being an owner myself), how sophomoric BMW
engineering really is.

Disclaimer: Yet, the drive train is phenomenal!

 

[Bimmer Owner]

Bet I can do it in less than half an hour - without the MaxiTester
and in about 5 or 10 minutes with it.

I'd be very happy to see pictures of the test leads in situ
because I personally tried (and succeeded) in getting the 40
amp blower motor fuse F76 out and back in, but I wouldn't
want to do it more than once in my life.

From memory, here's what I did:
.. I moved the passenger front seat as far back as I could
.. I lowered the passenger front seat back as far back as it goes
.. I removed the ignition key and disconnected the battery negative lead
.. I removed the panel from the bottom of the glovebox
.. I removed the Phillips screw and panel off to the passenger left kneecap
.. I lay upside down on the flattened passenger seat, head in the footwell
.. I located the general module III (GMIII)
.. With my arms bent wildly arms over my head, I disconnected harness connectors
.. The first enigmatic connector was the white connector X332
.. The next diabolical connector was the small black X253
.. And the last puzzling connector was the large black X254
.. By now, I could slightly see the yellow 40 & red 50 amp fuses F76 & F77
.. With a flathead 1/8" screwdriver, I lifted the yellow fuse F76 up & out
.. That took about an hour or three.
.. Putting the fuse back was even harder than removing it

 

[Bimmer Owner]

Has anyone ever fully dissected the unit so you can see what is under the PC
board? Maybe an X-ray from several angles done at the dentist?

All I have are the following:
These photos show both sides.
http://www.bimmerfest.com/forums/showthread.php?t=309399

Nothing was removed, so I can't figure out WHAT you guys are
saying is the transistor removed.

Can you circle one of these pictures to show WHERE you think
something was removed?

http://www.bimmerfest.com/forums/attachment.php?attachmentid=367580&d=1363957253
http://www.bimmerfest.com/forums/attachment.php?attachmentid=363800&stc=1&d=1361831815
http://www.bimmerfest.com/forums/attachment.php?attachmentid=363808&stc=1&d=1361837887

 

[[email protected]]

As for me, I fell sway to all the people saying how great the bimmer was.

It was only after I owned it, that I realized that BMW engineers knew
how to design a suspension and a drive train, but they had no idea
how to build a machine.

To their credit, some people say it's not the engineers fault as
they probably know by now that every single Bosch 5.7 ABS control
module fried in every one of the vehicles it was placed in, and that
the final stage unit cooked itself to death in every single BMW it
was ever placed in, and that the 2-bar plastic cooling system
sprang a leak on almost every single BMW ever built, etc.

In fact, there's absolutely NO WAY BMW can't know about these
egregious engineering flaws. So, the common conclusion is that
their customers don't care - so why should they.

To me, it smacks of 3rd-grade engineering from BMW, so, that's why
I, for one, am amazed (being an owner myself), how sophomoric BMW
engineering really is.

Disclaimer: Yet, the drive train is phenomenal!

If the engine desnt burn to the ground due to oil leaks, or overheat
or run out of oil, because of all the problems with "ancilliary
systems"

 

[Bimmer Owner]

that reduces the probability of it being rohs

What does ROHS mean?

 

[Scott Dorsey]

Can you circle one of these pictures to show WHERE you think
something was removed?

http://www.bimmerfest.com/forums/attachment.php?attachmentid=367580&d=1363957253

Okay, notice on the lefthand photo, there are two sets of three solder joints
on the lefthand side of the board, which show signs of recent rework. There
are TO-220 transistors attached to them, which are behind the board and you
cannot see.

On the righthand photo the board is reversed... you can see two sets of three
holes on the righthand side of the board which is where those TO-220
transistors were attached. You can see that they overheated the board and
lifted pads in the process too.

But you cannot in either of these photos see the transistors or what the part
number on the face of them is. Knowing what kind of transistors are used
will go far toward explaining some possible failure modes.
--scott

 

[tm]

Okay, notice on the lefthand photo, there are two sets of three solder
joints
on the lefthand side of the board, which show signs of recent rework.
There
are TO-220 transistors attached to them, which are behind the board and
you
cannot see.

On the righthand photo the board is reversed... you can see two sets of
three
holes on the righthand side of the board which is where those TO-220
transistors were attached. You can see that they overheated the board and
lifted pads in the process too.

But you cannot in either of these photos see the transistors or what the
part
number on the face of them is. Knowing what kind of transistors are used
will go far toward explaining some possible failure modes.
--scott

Yes, what Scott said. Where are the two transistors that were soldered in
the pair of three holes on the right of the right photo.

 

[jim beam]

THe problem is eddy currents at high pulse rates. Between the wire
used and the core you can get heating in the motor..

Most inverters or pulsers for industrial drives tend to operate in the
8kHz range, that seems to be a good compromise.

Another way to do this, is to have an inductor on board with the
speed control circuit. You would PWM that inductor in series to a filter
cap
on the output which will then give you a clean variable DC. THe inductor
will be doing all variable voltages.

ok, as i understand it, and as i said to scott earlier, this is a
problem because it mungs low speed motor start and low speed torque.

This is a form of a PFC type of
supply and the only heat you get is from the DC coil R in the inductor
and the heat from the switching MOSFET, which should both be rather
low. BY doing it this way, you could operate a switcher at lets say up
in the 100kHz or more range and this would keep the size of the caps and
inductor small.

It is cheaper to use the motor as the inductor for PWM control but,
it also can radiate noise on the lead wires. I guess one could actually
mount the speed control directly on the motor using PWM and the noise
problem should be minimum.

this seems to be the problem. you can get good efficient control at a
few hundred hz, but it's super noisy. if you take the frequency up
above audio, bigger motors seem to be more of an issue.

Calculating the cost between the two, BMW most likely decided to go
with the basic linear type, Because why should they care? It'll most
likely make it past it's warranty!

you got that right - and it would go a lot further past its warranty if
it was better rated.

 

[jim beam]

I'd be very happy to see pictures of the test leads in situ
because I personally tried (and succeeded) in getting the 40
amp blower motor fuse F76 out and back in, but I wouldn't
want to do it more than once in my life.

From memory, here's what I did:
. I moved the passenger front seat as far back as I could
. I lowered the passenger front seat back as far back as it goes
. I removed the ignition key and disconnected the battery negative lead
. I removed the panel from the bottom of the glovebox
. I removed the Phillips screw and panel off to the passenger left kneecap
. I lay upside down on the flattened passenger seat, head in the footwell
. I located the general module III (GMIII)
. With my arms bent wildly arms over my head, I disconnected harness connectors
. The first enigmatic connector was the white connector X332
. The next diabolical connector was the small black X253
. And the last puzzling connector was the large black X254
. By now, I could slightly see the yellow 40 & red 50 amp fuses F76 & F77
. With a flathead 1/8" screwdriver, I lifted the yellow fuse F76 up & out
. That took about an hour or three.
. Putting the fuse back was even harder than removing it

as said by others, buy a clamp-on current meter. it's not like you'd
never use it again.

 

[jim beam]

As for me, I fell sway to all the people saying how great the bimmer was.

It was only after I owned it, that I realized that BMW engineers knew
how to design a suspension and a drive train, but they had no idea
how to build a machine.

To their credit, some people say it's not the engineers fault as
they probably know by now that every single Bosch 5.7 ABS control
module fried in every one of the vehicles it was placed in, and that
the final stage unit cooked itself to death in every single BMW it
was ever placed in, and that the 2-bar plastic cooling system
sprang a leak on almost every single BMW ever built, etc.

honda use a "plastic cooling system". it's not infallible, but you can
get 15+ years out of the first one. there's no reason bmw couldn't
achieve the same - if they wanted to.

In fact, there's absolutely NO WAY BMW can't know about these
egregious engineering flaws. So, the common conclusion is that
their customers don't care - so why should they.

that is the catch - bmw target a certain type of buyer that typically
won't keep a car more than 3 years. after that, they don't care and bmw
can safely switch to "maximize parts sales/write off the old cars and
sell new ones" mode.

in europe, bmw have been aggressive leaders in "recycling" and spend a
lot of money advertising the fact. in practice however, it means that
they buy used cars back and have them scrapped, thereby keeping used
parts off the market - the mba's have done their math.

To me, it smacks of 3rd-grade engineering from BMW, so, that's why
I, for one, am amazed (being an owner myself), how sophomoric BMW
engineering really is.

it depends on perspective. i agree that some appear to be extremely
rudimentary, but that is contradicted by the fact that they spend a huge
amount of money on r&d, and have boatloads of phd's on staff. they were
also rescued by a bunch of mba's in the 70's and have had a root and
branch focus on design life ever since.

Disclaimer: Yet, the drive train is phenomenal!

call me when you have 100k miles on it...

 

[Jamie]

good point - how much? sure, big motor coils, big inductors -so how to
balance against pulse frequency for a bigger motor like a blower fan?

THe problem is eddy currents at high pulse rates. Between the wire
used and the core you can get heating in the motor..

Most inverters or pulsers for industrial drives tend to operate in the
8kHz range, that seems to be a good compromise.

Another way to do this, is to have an inductor on board with the
speed control circuit. You would PWM that inductor in series to a filter cap
on the output which will then give you a clean variable DC. THe inductor
will be doing all variable voltages. This is a form of a PFC type of
supply and the only heat you get is from the DC coil R in the inductor
and the heat from the switching MOSFET, which should both be rather
low. BY doing it this way, you could operate a switcher at lets say up
in the 100kHz or more range and this would keep the size of the caps and
inductor small.

It is cheaper to use the motor as the inductor for PWM control but,
it also can radiate noise on the lead wires. I guess one could actually
mount the speed control directly on the motor using PWM and the noise
problem should be minimum.

Calculating the cost between the two, BMW most likely decided to go
with the basic linear type, Because why should they care? It'll most
likely make it past it's warranty!

Jamie

 

[Bimmer Owner]

buy a clamp-on current meter

I have a Fluke 75, so I'll have to see what clamp on DC current
probes fit it.

 

[Bimmer Owner]

Yes, what Scott said. Where are the two transistors that were soldered in
the pair of three holes on the right of the right photo.

I always thought those were just "posts" tying the circuit board
to something inside the FSU - but I do agree that all the FSU
autopsies show those posts being unsoldered to remove the board.

Here's the quote that came with this picture, for example:
http://www4.picturepush.com/photo/a/12511542/img/12511542.jpg

 

[tm]

Ah, I see what you're talking about and I've circled them in this photo:
http://www3.picturepush.com/photo/a/12511526/img/12511526.jpg

Like a good detective, you've seen something that I had not seen.
What you said makes sense. However, I have never heard of anyone
removing two transistors from that board. I wonder if those two
sets of inline pins are just the connections to the heat sink?

Since I have an FSU in my possession, I will try to lift the board.
The FSU that I have, DOES have two sets of these "spikes" sticking up
at those very locations, so, clearly "something" is there.
http://www2.picturepush.com/photo/a/12511535/img/12511535.jpg

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.

No, they are two TO-220 cased transistors. they are most likely attached to
the heat sink somehow. Like was mentioned before, finding out the part
numbers on those transistors will reveal a lot.

tm

 

[Bimmer Owner]

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/12511554/img/12511554.jpg

 

[jim beam]

I have a Fluke 75, so I'll have to see what clamp on DC current
probes fit it.

cheaper to buy a whole new meter!

or google for this guy:
"ESI 695 80 Amps DC/AC Low Current Probe"

 

[Bimmer Owner]

Ah, I see what you're talking about and I've circled them in this photo:
http://www3.picturepush.com/photo/a/12511526/img/12511526.jpg

Looking more deeply, I find ANOTHER reference to the two MOSFETS,
which, are clearly the two transistors shown in the wiring diagram
that you had surmised must exist (by detective work).

Here's another quote which went along with this photo below
that mentions the unknown-as-yet MOSFETS:
http://www3.picturepush.com/photo/a/12511566/img/12511566.jpg