Root cause insight into the common BMW blower motor resistorfailures

In article >,
Bimmer Owner > 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."

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/sho...d.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/att...0&d=1363957253
> http://www.bimmerfest.com/forums/att...d=1361831 815

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/att...d=1361837 887


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.

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.

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.

dizzy wrote:
>
> jim beam > 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.

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/Restric...nces_Directive

nate

--
replace "roosters" with "cox" to reply.
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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/...g/12515572.jpg

tm > 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."

"Michael A. Terrell" > wrote in message
...
>
> 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.

"Bimmer Owner" > wrote in message
...
> 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/...g/12515572.jpg
>

Ha, keep going!