1980 240D - Window motor internal fuse?

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John B - 18 Sep 2004 05:14 GMT

I have removed the window motor from the right front door. Using a
continuity meter between the two wire leads, there is an obvious open
circuit. The motor winding, commutator, and brushes are fine; they show
continuity. There is a black, rectangular object inside the motor assembly,
in electrical series with an inductor. The black box is less than an inch
long, and says "9 017" on it. This black box fails to show any continuity
between its two terminals. I think it's a blown fuse.

Can anyone concur that this is a fuse?
Is there a chance I can buy such a fuse? Any tips on where to buy?
I'd rather not buy the entire motor, as that seems unnecessarily expensive.
If it's a blown fuse, it blew because someone I know was messing with the
mechanism. I'm confident there is no major problem, here.

Any idea what the amperage of such a motor fuse would be? I might need to
improvise.

Thanks,
John

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Tiger - 18 Sep 2004 15:21 GMT

No.. there is no user replaceble fuse in there... Try resoldering any joints
you see there.

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John B - 18 Sep 2004 17:55 GMT

Well, I put my continuity meter right across the terminals of the black box,
and it was "open." I just can't imagine what soldering would accomplish...
What would that thing be, that's in series with a rather large inductor?

> No.. there is no user replaceble fuse in there... Try resoldering any joints
> you see there.

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Paul - 18 Sep 2004 15:34 GMT

I am not familiar with this motor but on most P/W motors there is a
non-replaceable automatic resetting circuit breaker. The amperage varies as
does the shape and size. However anything is possible, just DON'T bypass it
as this could cause more problems than you have now. Try to select one with
just a little lower value than the fuse for the power windows.

Paul
Paul's Auto Electric

> I have removed the window motor from the right front door. Using a
> continuity meter between the two wire leads, there is an obvious open
[quoted text clipped - 15 lines]
> Thanks,
> John

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John B - 18 Sep 2004 18:02 GMT

I concur on your advise for the amerage of any over-current protection
device, within the motor assembly. It would be useless, unless it is less
than the amperage rating of the upstream fuse. I suppose there might be
other considerations, such as time-to-blow, etc. It makes complete sense
that, in a quality automobile like a MB, there would be an auto-resetting
circuit breaker in the motor assembly. Who would want to take the door
apart, to replace a fuse?

I didn't ring out the other door windows, because I didn't want to take the
door panels apart, for that purpose.

Shouldn't the two leads, coming out of the window motor assembly, show DC
continuity, when tested on the bench? I have removed it from the car,
entirely.

I have a beefy 13.8 VDC power supply, with which to bench-test the motor,
but I'm afraid the motor's armature would jump out of the brush position if
I did that. There's nothing holding the armature in position, axially. The
brushes would then implode into the axle, shorting out, and ruining
everything.

So doesn't a continuity test sound most appropriate?

Thanks,
John

> I am not familiar with this motor but on most P/W motors there is a
> non-replaceable automatic resetting circuit breaker. The amperage varies as
> does the shape and size. However anything is possible, just DON'T bypass it
> as this could cause more problems than you have now. Try to select one with
> just a little lower value than the fuse for the power windows.

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The earnest one - 18 Sep 2004 20:29 GMT

> I concur on your advise for the amerage of any over-current protection
> device, within the motor assembly. It would be useless, unless it is less
[quoted text clipped - 21 lines]
> Thanks,
> John

If I understand what you are saying the motor has been removed for an
assembly which gives the shaft support at the opposite end of the brushes.
If this is true you can't hardly do a bench test as is. If the shaft end is
supported in some sort of bearing, and it were me, I'd simply apply 12-14v
DC to the two terminals to see if the motor worked. If you have an open
circuit then you can hardly do any more damage to the unit than now exists.
It doesn't work now+...right? If that doesn't work I'd place the negative to
a ground on the motor and the positive to each of the terminals to see if
one takes it forward and the other backward. I don't think this is how it
works since the reversing of polarity (I believe) takes place at the window
switch itself. In this case my opinion would be, nothing ventured, nothing
gained.

> > I am not familiar with this motor but on most P/W motors there is a
> > non-replaceable automatic resetting circuit breaker. The amperage varies
[quoted text clipped - 4 lines]
> with
> > just a little lower value than the fuse for the power windows.

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