740 radio problems

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mgb - 24 May 2007 03:20 GMT

My 1991 740 wagon radio isn't working properly. When it's on there's a
terrible electronic noise coming from all speakers. The noise is worse when
I operate anything electric (power windows or turn signals for example). It
never gets better, only worse. Needless to say I don't operate the radio
(except to see if miraculously the problem might have stopped).

During the winter the area that houses the antenna motor became full of
water (drain plug was clogged). This is about the time the problem started,
but I can't put my finger on it exactly. I replaced the antenna motor and
the problem went away for about two months. Now the problem has returned.

Any ideas? I'm thinking a short in the wiring but I have never touched the
wiring so don't know how that could have happened.

I posted a similar question when this first happened (about three months
ago) and someone said there is a fuel relay that works double-duty as fuel
relay/"something to do with the radio". Has anyone heard of this? I fos,
where'w the fuel relay?

Thanks

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John Robertson - 25 May 2007 12:12 GMT

Aerial not connected to earth on body correctly, lube the aerial so it
slides well ,keep it clean ,disconnected aerial under the dash or radio end
or in the trunk ,boot .Most likely a poor contact where the aerial fits on
the external panel .

> My 1991 740 wagon radio isn't working properly. When it's on there's a
> terrible electronic noise coming from all speakers. The noise is worse
[quoted text clipped - 18 lines]
>
> Thanks

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Joe - 29 May 2007 00:55 GMT

> My 1991 740 wagon radio isn't working properly. When it's on there's a
> terrible electronic noise coming from all speakers. The noise is worse
[quoted text clipped - 18 lines]
>
> Thanks

There is a radio noise supression relay in my '87 740. I believe the one in
your car is located on the drivers side inner fender just in front of the
shock/strut tower.

joe

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Michael Pardee - 29 May 2007 13:18 GMT

>> My 1991 740 wagon radio isn't working properly. When it's on there's a
>> terrible electronic noise coming from all speakers. The noise is worse
[quoted text clipped - 23 lines]
>
> joe

IIRC even the gurus say they can't define which models/years had the relay
and which don't. My '85 765T doesn't. Ya never know until you look!

If I understand correctly, the presence of the relay suppresses ignition
noise by changing where the power for the ignition is picked up. Don't quote
me on that, and I hope somebody who actually knows will set me straight.

Mike

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mgb - 02 Jun 2007 17:19 GMT

Thanks everyone, Here's my latest update:

-Radio noise suppression relay. On my car it's on the passenger side,
mounted on the rad overflow reservoir. I replaced that but it didn't cure
the problem.

- bad earth problem. I was tracking down the bad earth suggestion at both
ends of the antenna, and with the antenna unplugged from both ends the
problem remained - so it wasn't that. Finally I noticed that when I
unplugged the amp cable at the back of the radio, the noise problem
disappeared. So, I accessed the amp, unplugged all the connections and
plugged them back in - eureka! Problem solved - perhaps after all this time
it was just a loose connection (knock on wood).

So far so good after two weeks.

Thanks to everyone for your help

MGB

>>> My 1991 740 wagon radio isn't working properly. When it's on there's a
>>> terrible electronic noise coming from all speakers. The noise is worse
[quoted text clipped - 32 lines]
>
> Mike

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Michael Pardee - 02 Jun 2007 17:33 GMT

> Thanks everyone, Here's my latest update:
>
[quoted text clipped - 15 lines]
>
> MGB

And thank you for the update. It will make it easier on "the next guy."

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