Root cause insight into the common BMW blower motor resistor failures

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.

I agree that the Extech meters are a good buy for the money. I have the

380947 (400 amp) and the 380942 (30 amp + voltmeter).

They are really handy to have in the toolbag.

tm

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.

Well, that's about what you need to know. Game over.

--scott

>

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.

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.

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

'Reduction Of Hazardous Substances'

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

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.

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

nate

Here's what the heatsink looks like when I cut into it today:

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

It's a variable voltage.

Still unknown.

Reported as DC.

--scott

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.

Ha, keep going!

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?)

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

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.

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 :).

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

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.

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 ...

Are those the two transistors sitting on top?