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Root cause insight into the common BMW blower motor resistorfailures

Discussion in 'Electronic Repair' started by Bimmer Owner, Mar 21, 2013.

  1. Jamie

    Jamie Guest

  2. Jamie

    Jamie Guest

    Yup, and I see the legs of the transistors (two). So those R's are in
    line with the emitters where they joint.

    Most likely thermo stress cracks due to the potting restraint.

  3. Jamie

    Jamie Guest

    THey make power resistors in T0-220 style cases, for heat sink mounting
    however, I doubt those are that.

  4. jim beam

    jim beam Guest

    fantastic. could you condescend to help these guys wit their project
    then? or are you just here to whang your donger around?

    then you're a complete genius because other people find it hard/impossible.

    yeah, a schematic doesn't exactly mean much if you don't even know what
    the components actually are. [see above]

    expensive? you're not kidding. and failure analysis is a whole lot
    easier if you know what you're looking at in the first place.

    yeah, if you know precisely where you're drilling, in three dimensions.
    and you have dil/soic [etc] type chips. anything bga or similar, and
    you're sol.

    and you're not doing that with a black box and getting meaningful data
    out of it.

    ok, but you're missing one simple thing - this is a bunch of guys with a
    dremel and a dental pick. money/time are limiting factors, even if
    there were logic to reverse engineering, which i don't think there is in
    this case.
  5. jim beam

    jim beam Guest

    no, what you're experiencing is her "disappointment" at discovering that
    you are an anosognosic retard.
  6. jim beam

    jim beam Guest

    didn't know.

    which would be another factor in favor of pwm...

    that would be my guess.

    i guess that's another part of what we're looking at here.

    thanks for the feedback!
  7. Jamie

    Jamie Guest

    If that being the case, I guess we now know why the module keeps burning
    out :)

    But there is factor that maybe you have forgotten or didn't know, and
    that is, the resistance of the DC motor. stall torque can be limited to
    what the DC R value is, in otherwords, this value forms a voltage
    divider and thus low voltage at stall current could seem like no voltage
    and not turn.

    DC PM/SHUNT motors attempt to compensate when load is dragging it
    down in speed, that also includes a slow start. So as long as the speed
    control can maintain a low voltage set point even when the motor is
    calling for high amps - the motor R, it'll still start. However, there
    is another factor, the speed control may not be performing armature feed
    back and simply supplying current only.. If this is the case, then the
    motor will stall at low speed demands in conditions that make it hard
    for the motor to start.

    I've also seen them allow the motor to run in torque mode to adjust
    for air density. It'll simply self adjust naturally, and in those cases
    you do not want armature feed back but torque feed back. Of course,
    this will cause heating of the module when torque demand is low..

  8. Guest

    No, because I'm not the one trying to reverse engineer
    an electronics module in a car, that contains among other
    things, an unknown 16 pin chip, without benefit of any of the
    necessary tools. You guys don't even know what the interface to the
    car is, whether it's analog or digital, etc. And you don't even have
    an oscilloscope to look at
    anything with.

    Oh, BTW, if you're all so smart, how come I was the
    first one to find out for you that the 16 pin chip number
    you had is a vaild one for a real chip?
  9. Scott Dorsey

    Scott Dorsey Guest

    Bosch has done the nichrome insert power resistor for many years; I know
    that they used them in the turn signal flasher in the late seventies when
    they first went electronic. They aren't really very good resistors but
    they are very cheap.
  10. Scott Dorsey

    Scott Dorsey Guest

    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:

    (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.)
  11. jim beam

    jim beam Guest

    so what you're saying is that you're just here to piss and moan because
    you know how to help, but won't.

    and credentials don't work on usenet - they're completely uncheckable
    and many are bogus. what matters is whether you can walk the talk.

    as for having stuff in orbit, i don't have anything, but two of my best
    friends do. the difference between them and you is that they're not
    jaded and they're actually helpful.

    that at least is vaguely useful, but you could have come up with that 20
    posts ago.
  12. jim beam

    jim beam Guest

    i don't know who you think you're talking to, but i have consistently
    advocated /not/ deconstructing this unit. it's not worth it when cost
    of replacement isn't that high or you can build an alternate controller
    that will be more reliable.

    at least i can follow a thread without being a crotchety old fart.

    i don't /want/ to reverse engineer it any more than i want to repair
    broken light bulbs. you were the one bragging about how easy it was. i
    said it wasn't. and when it comes down to walking the talk, you won't.

    i guess we should be grateful...
  13. Leif Neland

    Leif Neland Guest

  14. Scott Dorsey

    Scott Dorsey Guest

    That's why there are exemptions for the military and telecom industry,
    where it's actually important that stuff work properly.

    What I find ironic is that the shorter lifespan of consumer gear caused by
    the RoHS manufacturing has actually increased the amount of electronics
    going into landfills, making worse the problem that it was intended to reduce.
  15. Bimmer Owner

    Bimmer Owner Guest

    Most of the people on the BMW forums think it's one of these.
  16. Bimmer Owner

    Bimmer Owner Guest

    Other people have suggested this also.

    Some say the potting is what is causing the stress cracks.

    Re-insert without potting, is the "said to be" solution.

    One question:
    If the FSU works without potting, what was the purpose of the potting?
  17. Bimmer Owner

    Bimmer Owner Guest

    Good catch!
  18. Bimmer Owner

    Bimmer Owner Guest

    I will try this morning. (I was away on a trip for the past two days).

    PS: Had to look up araldite:
  19. Bimmer Owner

    Bimmer Owner Guest

    The red jumper was a hack added by one user to fix the solder cracks,
    I think.
  20. Bimmer Owner

    Bimmer Owner Guest

    This implies two transistors (although I only found one).

    I will dig through the mess again - but I think I was too fat thumbed
    when I cut it open, and may have destroyed the evidence.

    I do have a second FSU (since two failed on me) though ... but I want
    to try to FIX that one (instead of destroying it).
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