Root cause insight into the common BMW blower motor resistor

[trader4@optonline.net]

On Mar 25, 2:55 pm, klu...@panix.com (Scott Dorsey) wrote:

Bimmer Owner  <dontask...@mymail.com> wrote:



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....

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
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Maybe it's time to look at this thing like gas and brakes...
You put gas in, you go so far. You put one of these
blower modules in and you go for a few years again.
It's not like they are a $500 or $1000 puter. Don't they
cost like $50? I mean how much is time worth trying
to reverse engineer it.....

 

[dizzy]

jim beam <me@privacy.net> wrote:

i wish something would stop you. like self-awareness.

Says the idiot who says it overheats "because it's linear", as if
proper design (adequate heat-sinking) can't prevent overheating in a
"linear" design. Sheesh.

 

[dizzy]

Bimmer Owner <dontaskfor@mymail.com> wrote:

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

I must be lucky. My 2000 323 has had only one of the above "failures"
- leaky power-steering hoses.

 

[jim beam]

On 03/25/2013 05:57 PM, Jamie wrote:

jim beam wrote:

On 03/24/2013 02:30 PM, Jamie wrote:

amdx wrote:

that looks like a linear semiconductor controller - an incredibly
antiquated concept for a modern car.

well, you live and learn. apparently the reason they use a linear
controller is because it allows the fan to run near silently at low
speed. with pwm control the fluctuating magnetic fields in the
motor >coils cause it to vibrate and make a humming noise at the pwm
control >frequency.

that doesn't of course get around the fact that the unit in question
here is apparently badly under rated, but the above does at least
explain why it's used.

I see many Motor Speed Control Manufacturers upped their PWM
frequency to be between 16 K to 22 K to eliminate much of the noise.
Mikek

Sure, if you don't mind heating the motor up...

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.

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.


--
fact check required

 

[jim beam]

On 03/25/2013 10:13 AM, Bimmer Owner wrote:

On Mon, 25 Mar 2013 12:26:52 -0400, clare wrote:

I'd wager it 'can' be done - it's just going to take an hour or so
to get the leads in place.
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

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


--
fact check required

 

[jim beam]

On 03/25/2013 09:54 AM, Bimmer Owner wrote:

On Sat, 23 Mar 2013 07:20:44 -0700, jim beam wrote:

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.

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...


--
fact check required

 

[Jamie]

jim beam wrote:

On 03/24/2013 02:30 PM, Jamie wrote:

amdx wrote:

that looks like a linear semiconductor controller - an incredibly
antiquated concept for a modern car.

well, you live and learn. apparently the reason they use a linear
controller is because it allows the fan to run near silently at low
speed. with pwm control the fluctuating magnetic fields in the
motor >coils cause it to vibrate and make a humming noise at the pwm
control >frequency.

that doesn't of course get around the fact that the unit in question
here is apparently badly under rated, but the above does at least
explain why it's used.

I see many Motor Speed Control Manufacturers upped their PWM
frequency to be between 16 K to 22 K to eliminate much of the noise.
Mikek

Sure, if you don't mind heating the motor up...

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

 

[tm]

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kir7q6$hpn$2@news.albasani.net...

On Mon, 25 Mar 2013 14:55:02 -0400, Scott Dorsey wrote:

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.

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

 

[jim beam]

On 03/25/2013 08:56 PM, Bimmer Owner wrote:

On Mon, 25 Mar 2013 17:34:25 -0700, jim beam wrote:

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.

cheaper to buy a whole new meter!

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


--
fact check required

 

[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/12511554/img/12511554.jpg

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.


--
fact check required

 

[Bimmer Owner]

On Mon, 25 Mar 2013 17:34:25 -0700, jim beam wrote:

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]

On Mon, 25 Mar 2013 14:55:02 -0400, Scott Dorsey wrote:

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.

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.

 

[jim beam]

On 03/25/2013 10:02 PM, Bimmer Owner wrote:

The mesure of the DC voltage on those resistors can be used to
evaluate the current of the blower and its worn state.

What does this sentence above mean?

with two resistors in series, the voltage across any one is a function
of its resistance and the current in the current in the other.

Does it intimate the blower motor is actually drawing more
current as it ages (as someone had suggested prior)?

good question - there might be a slight change in draw as the motor
ages, but unless the motor has serious bearing health issues or blows a
magnet coil, i can't imagine it will change by much. and other than
short circuit detection/protection, i have doubts about the extent to
which such a simple controller will need to know.


--
fact check required

 

[Bimmer Owner]

On Mon, 25 Mar 2013 18:12:53 -0400, tm wrote:

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

Ok, here are a couple of pics of my FSR from a 2002 E46
which is identical to FSR's in many other models and series of BMW.
The first is what you see when you scrape off the epoxy-like filling
covering the PCB. Using a hairdryer or better still a heatshrink gun
carefully without overheating. If you smell burning its too hot.
You should get a faint hot plastic odour that's all. I used one of
those cheap sets of precision flat screwdrivers, they can be sharp
so again be careful. You can see I gouged and scratched the circuit
board a little in places, just make sure you don't slice through any
tracks or lever off any components.
The second picture is a zoom of the 2 groups of 3 pins which I
believe are the cause of my FSR going crazy. If you look closely,
all six pins have cracks in the solder around the pins, most noticeable
are pins 1, 4 and 5 from left to right. My repair was simply to remelt
and resolder these pins with a little more solder using a hot and fine
tipped soldering iron, until I felt that the lead had flowed through
the board and hopefully to the other side where the components/resistors
are. If this repair doesn't last, I may remove the board fully and have
a better look on the other side.

 

[Bimmer Owner]

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/12511554/img/12511554.jpg

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

 

[Bimmer Owner]

On Tue, 26 Mar 2013 04:22:30 +0000, Bimmer Owner wrote:

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

The 2 MOSFET drain and source are tied together but the gates are differents

On the picture , one of the component is gone with the rubber foam : its
look like transistor : black with 3 pins ( it 's not bipolar transistors ).

It happen to me also : the component gone so easily that I didn't realize it,
maybe it is the issue for that FSU.

It is only while I compare to other pictures in the forum that there was
a lack of component on my board.

fortunately I found it together with the rubber foam parts, so I will
solder it back later

 

[Bimmer Owner]

On Mon, 25 Mar 2013 21:42:16 -0700, jim beam wrote:

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

This seems to only be $107 but it doesn't say whether it works
with the Fluke 75 or not.
http://www.amazon.com/ESI-695-Amps-Current-Probe/dp/B000FN4IUK

 

[Bimmer Owner]

On Tue, 26 Mar 2013 00:39:23 -0400, tm wrote:

they are two TO-220 cased transistors.
finding out the part numbers on those transistors will reveal a lot.

I have an FSU in my possession, so I will dig them out & snap
a photo when done and post back the results.

To my knowledge, nobody has ever posted a photo of what those
two MOSFETS look like, nor the part number.

 

[Bimmer Owner]

The mesure of the DC voltage on those resistors can be used to
evaluate the current of the blower and its worn state.

What does this sentence above mean?

Does it intimate the blower motor is actually drawing more
current as it ages (as someone had suggested prior)?

 

[tm]

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kir99g$hpn$5@news.albasani.net...

On Tue, 26 Mar 2013 04:22:30 +0000, Bimmer Owner wrote:

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

The 2 MOSFET drain and source are tied together but the gates are
differents

On the picture , one of the component is gone with the rubber foam : its
look like transistor : black with 3 pins ( it 's not bipolar
transistors ).

It happen to me also : the component gone so easily that I didn't realize
it,
maybe it is the issue for that FSU.

It is only while I compare to other pictures in the forum that there was
a lack of component on my board.

fortunately I found it together with the rubber foam parts, so I will
solder it back later

As a general rule, MOSFETs are not used for linear current control. It is
more looking like this is a switcher (PWM) though I dont see an inductor.
Could be they just use the motor for that.

If you can see any numbers on the devices, it will help. Also, the solder
sure looks like RoHS shit tin.