Root cause insight into the common BMW blower motor resistor failures

Page 6 of 9  
On Mon, 25 Mar 2013 14:55:02 -0400, Scott Dorsey wrote:

Ah, I see what you're talking about and I've circled them in this photo:

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.

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

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

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:

[QUOTE=olivier577]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[/QUOTE]
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On Tue, 26 Mar 2013 14:09:11 -0400, Michael A. Terrell wrote:

It might be, but this Russian site intimates it's a temperature compensated voltage controller. http://tinyurl.com/crg2sms http://kazus.ru/schematics/electrical-engineering/search/go/?text=%D0%C5%C3%D3%CB%DF%D2%CE%D0%20ELMOS%2010901D&nohistory=1&h=1 http://monitor.espec.ws/section27/topic189041.html http://item.taobao.com/item.htm?id 918440884
Translation below: REGULATOR ELMOS 10901D Found: 100 Showing: 1 - 10 Car Voltage Regulator Category: Car Source: Radioland country Electronics Temperature controller cabin air KAMAZ Category: Car Source: Plans radiokonstruktsy Simple Temperature compensated voltage regulator. Controller together with thyristor-transistor electronic ignition unit with a long spark, ensuring the rapid start-ups at various operating conditions, allowed to increase battery life of up to nine years. Category: Car Source: For the life of a soldering iron ... Regulator for automotive windshield Category: Car Source: MASTER KIT The controller measures the wiper-this control is designed to use regular mode switch blades and is contactless. Category: Car Source: For the life of a soldering iron ... Temperature compensated voltage regulator device in some ways superior designs. The controller can be used as a universal device is suitable not only for mounting on any car, but everywhere, where the generator rotor speed is variable (eg, wind power). Choose the appropriate control elements, it can be easily adapted to work with any voltage (up to 400V) and excitation current (tens of amperes). Category: Car Source: For the life of a soldering iron ... Voltage regulator 2012.3702, 22.3702, 221.3702 Category: Car Source: For the life of a soldering iron ... Voltage regulator 201.3702 Category: Car Source: For the life of a soldering iron ... Voltage Regulator 13.3702 Category: Car Source: For the life of a soldering iron ... Voltage regulator RR132A, 1112.3702 Category: Car Source: For the life of a soldering iron ...
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Bimmer Owner wrote:

Be careful with so called information from those types of sites. Most of their information is badly translated, or just plain wrong. Tabao.com is a prime example of crap information. I have never found correct information there. Most is from chinese Ebay sellers who make things up about items they sell. They have no idea what it is, just that they can sell it on Ebay or Tabao.com.

thyristor-transistor electronic ignition unit with a long spark, ensuring the rapid start-ups at various operating conditions, allowed to increase battery life of up to nine years.

designs. The controller can be used as a universal device is suitable not only for mounting on any car, but everywhere, where the generator rotor speed is variable (eg, wind power). Choose the appropriate control elements, it can be easily adapted to work with any voltage (up to 400V) and excitation current (tens of amperes).

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

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:

[QUOTE=olivier577] 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[/QUOTE]
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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.
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It's not a switcher. And those transistors may not be MOSFETs. But there is no reason not to use mosfets in linear mode, other than the fact that no two off the line have the same gain or transconductance.

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

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No, there are two transistors bolted to the heat sink. That's why the heat sink is there, to cool those two power transistors.

No, the spacing is consistent with a TO-220 transistor pair, and if it's a linear pass regulator like it appears to be, there needs to be a big transistor somewhere. Also, of course, there is the heatsink.
That IC is only control logic, it just takes some mystery input signal and produces a variable voltage for the transistor base. Those two transistors are doing all the hard work. BUT, if you want to replace the device with a retrofit one, you need to know what that mysterious input signal is. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On Mar 26, 9:10 am, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

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One key question in all this is if the interface from car to "resistor block" is some kind of simple digital interface, ie it sends some bits that get interpreted as "go to speed 3" or does it send a PWM signal. My guess is the latter. That's my understanding of what BMW does with the aux radiator fan in the X5. Another German electronic miracle that fails and in doing so, mysteriously drains the battery.
Someone should put an oscilloscope on this and find out what the signal looks like. If it sends a digital code, then making a replacement from scratch is a big hurdle. If it's sending a PWM signal, they you could build an equivalent from Radio Shack parts. It still seems like more work than it's worth.
How fast are these things failing for those that want to make their own? 2002 X5 here and it's only had this problem once, about 2 years ago and replacement one is still working. And another data point. The failure on that X5 resulted in the blower draining the battery when the car was off. Blower ran fine. Only odd thing in retrospect was that when the car was off, a couple times I heard a faint noise. In retrospect, it was probably the blower getting just enough current to start to turn then stop. And only noticed it a couple times. The bad thing with the failure mode of this and the AC fan is that both were draining the battery and both were very hard to pinpoint, resulting in huge labor charges.
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On Tue, 26 Mar 2013 07:37:09 -0700, snipped-for-privacy@optonline.net wrote:

All I know is that the HVAC controller sends a 2.0 VDC to 7.8 VDC signal to one of the five pins of the FSU. I presume that directly corresponds to the desired blower motor speed - but that is conjecture on my part.

The originals fail within about 5 years. I've had my second one fail in 3 years. I think we can safely say about 3 to 5 years is the lifecycle but nobody really knows for sure (least of all me).

This is one of the classic failure indications! Very very very common! However, another classic failure indication, other than the dead battery in the morning, is a blower that has a "mind of its own".
Together, those two sets of symptoms account for 99% of the failures.
Of all the anecdotal evidence presented, I don't think I've ever heard of a failure being that the system was totally dead.
What that tells us, I don't know.
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snipped-for-privacy@optonline.net wrote:

Your idea about testing it is correct, however a bad one can work fine until it gets hot enough for the IC chip to fail. Hvac control voltage is 0-8 VDC.
The load resistor should have a metal case mounted on a heatsink to dissipate the heat if you are going to run the test more than a few minutes.
My original 13 spike FSU was replaced twice under warranty, so the car had 3 FSU's. When the 3rd old style failed i replaced it with the new design FSU. That was 8-9 years ago, it is still working. One thing not considered in your post is how many did not use OEM units, the $75 eBay ones are junk. The $175 units at the stealer seem to hold up a little better.
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On Tue, 26 Mar 2013 09:10:56 -0400, Scott Dorsey 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.
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But is that a clean DC level or a pulse width modulated signal? If it was measured with a multimeter, you won't know.
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
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o

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.

ble

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

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

Are those the two transistors sitting on top?
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On Tue, 26 Mar 2013 15:04:51 -0400, tm wrote:

Actually, it's the same transistor, which broke in half while I was attempting to get the black rubber eraser stuff off of it to read the numbers.
It's really going to be HARD to read those numbers now...

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Okay, there is a TO-220 package that is split open there, with the backplate on the right and the cover on the left. Can you chip off enough of the araldite from the cover to be able to read the numbers on it?
Or, could you get a good picture of the die which is left on the piece on the right? We might be able to identify it with a sharp photo of the die... although from what I can see from the fuzzy photo it does not look like a very happy die.
If it is actually a MOSFET it will look like this:
http://www.panix.com/~kludge/fet1.jpg
(That's a package that is a little bigger than the TO-220, but you can still see the channel down the middle of the FET and the overheating damage to the source.... the three leads have been torn off in the unpotting process though.) --scott
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