Root cause insight into the common BMW blower motor resistor

[Francis C.]

Scott Dorsey wrote:

trader4@optonline.net <trader4@optonline.net> wrote:
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.....

Bear in mind that the $75 Sitronic Ebay FSU is known to be even
more faulty than the $175 Valeo FSU from the stealer.

I can think of nice test equipment to buy instead of a $175 FSU every
few years!

 

[Bimmer Owner]

On Tue, 26 Mar 2013 15:30:41 +0000, Bimmer Owner wrote:

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC signal
from the HVAC controller, presumably to correspond to the various levels
of the fan blower motor speed.

Here is a picture of the BMW E39 HVAC/IHKA controller and sampling fan.
http://www4.picturepush.com/photo/a/12514687/img/12514687.jpg

I'm googling for specs as we speak.

 

[Michael A. Terrell]

jim beam wrote:

if it's just a two-layer board, maybe. assuming you get the specs on
the chips of course. but you'll need more than two units and a whole
lot of patience trying to reverse the schematic if it's 4 or more
layers. and you still don't achieve anything more than having a broken
light bulb in your hand.

what you need to do is get the operational capacities of the /working/
unit, and work with those. that the unit is a black box is completely
irrelevant.

Yawn. I worked with 16 layer boards at a factory troubleshooting
defective, new boards that cost over $8,000 to stuff. The internal
routing of a simple low frequency board is irrelevant for drawing a
schematic. You can X-ray a board or mill it one layer at a time if you
want to duplicate the routing. All you need to do for bais reverse
engineering is to trace each with an ohm meter by probing every pad and
termination to identify the signal path and draw a schematic from your
notes. I've done this with four layer boards for 30+ years. "Specs on
the chips" makes things easier but knowing who made it, and how it's
connected will tell you if it is a custom part or just house numbered.

There are industrial solvents to remove any potting compound, but
they aren't cheap or easy to buy. Failure analysis is a specialty in
electronics manufacturing. It is expensive but gives you the answers
you need so you can design out the problems.


A jig to hold the module in a CNC machine would allow you to cut
accurate holes down to the right points to see if the IC was bad,
without unpotting a failed unit. Then a test fixture with 'Pogo Pins'
would allow you to see what was bad. If there were enough bad units, it
would be worth designing and programming a computerized fixture.

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[trader4@optonline.net]

On Mar 26, 11:53 am, "tm" <No_one_h...@white-house.gov> wrote:

"Bimmer Owner" <dontask...@mymail.com> wrote in message

news:kisev1$ott$2@news.albasani.net...

On Tue, 26 Mar 2013 09:10:56 -0400, Scott Dorsey wrote:

BUT, if you want to replace the device with a retrofit one, you need to
know what that mysterious input signal is.

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC
signal from the HVAC controller, presumably to correspond to the
various levels of the fan blower motor speed.

But is that a clean DC level or a pulse width modulated signal? If it was
measured with a multimeter, you won't know.

The other possibility is that it's a digital command signal of
some kind. I don't know how they typically do that, but if a
0 is 0 volts and a 1 is 12V, for example, looking at it with a
volt meter, you would see a range like that given.
They do have that 16 pin chip there, doing something.
It might receive the command and then output the appropriate
PWM for rest of the circuit.

Has anyone probed around the module with a scope? Is that possible?

That and the question about the TO-220 devices. I think it would be possible
to make a better replacement if those questions were answered.

tm

 

[Scott Dorsey]

In article <kisev1$ott$2@news.albasani.net>,
Bimmer Owner <dontaskfor@mymail.com> wrote:

On Tue, 26 Mar 2013 09:10:56 -0400, Scott Dorsey wrote:

BUT, if you want to replace the device with a retrofit one, you need to
know what that mysterious input signal is.

All I know of the HVAC input signal is that it's a 2.0 to 7.8 VDC
signal from the HVAC controller, presumably to correspond to the
various levels of the fan blower motor speed.

Well, that's about what you need to know. Game over.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[Michael A. Terrell]

Bimmer Owner wrote:

On Mon, 25 Mar 2013 09:42:51 -0400, Michael A. Terrell wrote:

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

Do you see the two groups of three empty holes on the right side?
They look like cracked solder joints on TO-220 packages which could be
semiconductors or power resistors.

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

You can see the leads in those holes, in this photo. They look
cracked. That is a common failure due to stress caused by uneven
heating of potted components.

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[Michael A. Terrell]

Bimmer Owner wrote:

On Mon, 25 Mar 2013 22:23:22 -0700, jim beam 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.

Ah, so it's a plain old voltage divider?

I think the IC is a dual, high side motor driver IC and each
transistor has a large emitter resistor with different values. That is
the metal strips on the pins by the sets of three holes. That would
give three speeds & off. Like a three way lamp with 50 + 100 Watt
elements. Turn both on and it draws 150 Watts. This would explain the
failure of the solder joints on the transistors since they are used in
linear mode.

00 would be off
01 would be low speed
10 would be medium speed
11 would be high speed

--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[Michael A. Terrell]

Bimmer Owner wrote:

On Mon, 25 Mar 2013 07:55:03 -0700, jim beam wrote:

that reduces the probability of it being rohs

What does ROHS mean?

'Reduction Of Hazardous Substances'

Crappy lead free solder that cracks with a lot less stress that
leaded solder. Brought to electronics by European bureaucrats.


--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[Michael A. Terrell]

dizzy wrote:

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.

Sheesh indeed. That heatsink is small. Sure, it will work for a
while, but it isn't designed for long life. Depending on forced air
cooling when the air is either heated or cooled is just plain stupid.


--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[Nate Nagel]

On 03/25/2013 01:58 PM, Bimmer Owner wrote:

On Mon, 25 Mar 2013 07:55:03 -0700, jim beam wrote:

that reduces the probability of it being rohs

What does ROHS mean?

Restriction of Hazardous Substances; that is, no lead (among other things.)

http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substances_Directive

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

 

[Scott Dorsey]

tm <No_one_home@white-house.gov> wrote:

That's a good theory except why would the resistors not be attached to the
heat sink?

Because they draw no current, they only set the base bias of the power
transistors.

There are still open questions that until answered we are just speculating
with educated guessing.

1) What exactly does the control signal look like on a scope?

It's a variable voltage.

2) The two devices, mosfets or transistors? Any part numbers?

Still unknown.

3) Waveforms on the motor power line for the different speeds.

Reported as DC.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

 

[tm]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:ba6dnXAvZ-jVeczMnZ2dnUVZ_vidnZ2d@earthlink.com...

Bimmer Owner wrote:

On Mon, 25 Mar 2013 22:23:22 -0700, jim beam 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.

Ah, so it's a plain old voltage divider?



I think the IC is a dual, high side motor driver IC and each
transistor has a large emitter resistor with different values. That is
the metal strips on the pins by the sets of three holes. That would
give three speeds & off. Like a three way lamp with 50 + 100 Watt
elements. Turn both on and it draws 150 Watts. This would explain the
failure of the solder joints on the transistors since they are used in
linear mode.

00 would be off
01 would be low speed
10 would be medium speed
11 would be high speed

--

That's a good theory except why would the resistors not be attached to the
heat sink?

There are still open questions that until answered we are just speculating
with educated guessing.

1) What exactly does the control signal look like on a scope?

2) The two devices, mosfets or transistors? Any part numbers?

3) Waveforms on the motor power line for the different speeds.

 

[tm]

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kisq1q$jpd$1@news.albasani.net...

On Tue, 26 Mar 2013 14:23:08 -0400, Michael A. Terrell wrote:

That heatsink is small.

Here's what the heatsink looks like when I cut into it today:
http://www4.picturepush.com/photo/a/12515572/img/12515572.jpg

Ha, keep going!

 

[Nate Nagel]

On 03/26/2013 12:35 PM, tm wrote:

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kisfan$ott$4@news.albasani.net...
On Tue, 26 Mar 2013 08:56:22 -0400, Scott Dorsey wrote:

one person figuring the failure mode out might save a
lot of people that grief.

But mostly it's just intellectual curiosity.

Exactly!


I don't even own a BMW. After this thread, I don't think I ever will.

Like I said before, don't drive one then. It's kind of like going on a
date with that unbelievably attractive female type who is also smart,
witty, fun to be around, actually seems to like you, and oh by the way
is completely mentally unhinged.

Suddenly you find yourself putting up with all sorts of stuff that you
wouldn't, otherwise... (now that said, touch wood, current ride has
exhibited none of the known issues... which reminds me, I need to call
and schedule the battery cable recall @ the stealership)

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

 

[tm]

"Scott Dorsey" <kludge@panix.com> wrote in message
news:kisq65$i86$1@panix2.panix.com...

tm <No_one_home@white-house.gov> wrote:

That's a good theory except why would the resistors not be attached to the
heat sink?

Because they draw no current, they only set the base bias of the power
transistors.

There are still open questions that until answered we are just speculating
with educated guessing.

1) What exactly does the control signal look like on a scope?

It's a variable voltage.

Are you sure? It seems it was measured with a DMM, not a scope. A PWM signal
would just look like DC to a DMM.
Since it was reported as "2.0 to 7.8" volts, you would not get those
significent figures with a scope.

2) The two devices, mosfets or transistors? Any part numbers?

Still unknown.

3) Waveforms on the motor power line for the different speeds.

Reported as DC.

Any evidence it was checked with a scope? Again, a PWM signal will just look
like a DC level to a DMM.


Let's see what the autopsy shows next .

 

[tm]

"Nate Nagel" <njnagel@roosters.net> wrote in message
news:kisqep418lt@news4.newsguy.com...

On 03/26/2013 12:35 PM, tm wrote:

"Bimmer Owner" <dontaskfor@mymail.com> wrote in message
news:kisfan$ott$4@news.albasani.net...
On Tue, 26 Mar 2013 08:56:22 -0400, Scott Dorsey wrote:

one person figuring the failure mode out might save a
lot of people that grief.

But mostly it's just intellectual curiosity.

Exactly!


I don't even own a BMW. After this thread, I don't think I ever will.

Like I said before, don't drive one then. It's kind of like going on a
date with that unbelievably attractive female type who is also smart,
witty, fun to be around, actually seems to like you, and oh by the way is
completely mentally unhinged.

Suddenly you find yourself putting up with all sorts of stuff that you
wouldn't, otherwise... (now that said, touch wood, current ride has
exhibited none of the known issues... which reminds me, I need to call
and schedule the battery cable recall @ the stealership)

nate

--

LOL. There's more truth to that then you may think.

 

[tm]

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

On Tue, 26 Mar 2013 09:43:58 -0700, trader4@optonline.net wrote:

They do have that 16 pin chip there, doing something.
It might receive the command and then output the appropriate PWM for
rest of the circuit.

Someone had scoped the whole board, and it was DC voltage everywhere
(according to that reference). It's pretty clear there is no PWM.

The 16-pin surface mount chip seems to be a automotive temperature
compensated voltage regulator with a huge voltage range, according
to a lookup of the part number on it.

Here is the Elmos 10901D chip of my FSU as I cut it open today.
http://www4.picturepush.com/photo/a/12515632/img/12515632.jpg

I wish there was a way to get rid of that heavy fibrous plastic goop!
(What is that black fibrous tough stuff anyway?)

Are those the two transistors sitting on top?

 

[Scott Dorsey]

Bimmer Owner <dontaskfor@mymail.com> wrote:

I wish there was a way to get rid of that heavy fibrous plastic goop!
(What is that black fibrous tough stuff anyway?)

It's an epoxy resin filled with silica. It will come off with DMSO at
three atmospheres or so. Sometimes a soak in DMSO for a couple weeks will
make it peel off. This will also soften the PC board though.
--scott

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

 

[Bimmer Owner]

On Tue, 26 Mar 2013 14:23:08 -0400, Michael A. Terrell wrote:

That heatsink is small.

Here's what the heatsink looks like when I cut into it today:
http://www4.picturepush.com/photo/a/12515572/img/12515572.jpg

 

[Bimmer Owner]

On Tue, 26 Mar 2013 09:43:58 -0700, trader4@optonline.net wrote:

They do have that 16 pin chip there, doing something.
It might receive the command and then output the appropriate PWM for
rest of the circuit.

Someone had scoped the whole board, and it was DC voltage everywhere
(according to that reference). It's pretty clear there is no PWM.

The 16-pin surface mount chip seems to be a automotive temperature
compensated voltage regulator with a huge voltage range, according
to a lookup of the part number on it.

Here is the Elmos 10901D chip of my FSU as I cut it open today.
http://www4.picturepush.com/photo/a/12515632/img/12515632.jpg

I wish there was a way to get rid of that heavy fibrous plastic goop!
(What is that black fibrous tough stuff anyway?)