Re: bmw-digest V9 #159

[Bob Hazelwood <woodyh@xxxxxxxxxxxxx>]

> Jason Bell Asked:
>
> Good Afternoon Everyone,
>
> <snip> I'm hoping
> someone can help me out with some puzzling problems I'm having with my
> stereo.
>
> <snip> the tuner will cut out intermittently. <snip> About a
> week ago, my power antenna would automatically lower (and sometimes
> re-extend itself) for unknown reasons, which would cut out the tuner
> reception.  (I solved that by quickly turning the stereo off and back on.)
> But now the antenna is fine and stays extended whenever the stereo power is
> on.  The cassette player works perfectly.  The only problem is that
> sometimes the tuner works, and other times it is just emits silence.
>
> I had my mechanic look at it the other day (when the antenna was lowering
> itself) and he seemed to think that the problem was a bad amp that was
> cutting off power to the stereo and antenna.  He said that a factory amp
> would be too expensive and I should just buy an aftermarket stereo.

Your mechanic may be great with the hard metal parts bathed in grease, but I
suspect he's off the mark in his audio diagnosis. The system's main amp amplifies
the signal to the speakers the same for the radio as it does for the cassette. The
amp does not supply power _to_ the radio, it takes the _output_ of the radio,
increases it's voltage, and sends that stronger signal to the speakers. Therefore
if the cassette is not giving you trouble then the amp is not the problem.

I don't think that your car has a separate antenna amp, at least my 87 E30 didn't.
But if it does this could cause the problem you describe. I may be wrong, but I
don't think that BMW started putting antenna amps in until they went to the rear
window antennas on the E34 and E36's.

My first guess is that your problem is what we in the audio biz call
"connectoritis". In your case I'll bet that your problem is related to an
intermittent connection somewhere in the antenna wiring. This could be caused by
corrosion at the antenna location or a broken wire connection anywhere along the
length of the antenna wire. Odds are it is at one end or the other. I'd look here
first. You can check it by connecting a separate antenna to the jack at the back
of the radio and just sitting it on the seat next to you. The reception won't be
great, but it should give you something to help identify if the problem is in the
radio or external to it.

If that's not it, the next most likely candidate is an problem in the power
switch. I've seen the solder connections break from age/stress at the point where
the power switch/volume control attaches to the PC board instde the radio. This is
a pretty trivial repair for a radio tech, which should be minimal in cost. It is
possible for a problem here to not affect the cassette, depending on the
particular connection which is broken. The antenna going up/down would come from
power being lost to the white wire. ("white" assumes that the wiring is the same
as it was in my '87 325 your '89 may be slightly different) This is the wire which
triggers the antenna to extend when the radio is on. This also tells the power amp
to turn on, so if the antenna is going down but the power amp remains on, (which
it would have to do to hear your cassettes,) it indicates that the problem is
likely in the antenna wiring.

The third likely suspect is the internal power supply regulator which regulates
the tuner's power supply voltage. They are subject to a lot of thermal stress in
operation so it is not unusual for them to become intermittent. The cassette has
its own. Again, this is one of the first things a technician will look for.

There are a hundred more things internal to the radio which could be causing this.
The above three are the most common ones which are easily/inexpensively fixable.
The parts are not expensive, but like a mechanic, you're paying for diagnostic
time with arepair technician, so anything beyond this could take awhile to find.
In that case you are probably better off trying to buy a replacement radio. It
will probably not cost you much more than the repair bill for a harder to diagnose
problem. You will see used factory take-out radios posted here on the Digest quite
often.

Hope this helps!

Best regards,
Bob Hazelwood
VP Product Management, a/d/s/
'93 525i 5-sp, Sharked
BMW CCA 115184 (Boston)


PS. Don't wait til Christmas for the chip!

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