Deafening Interference sound coming out of speakers

[Garageaholic]

i have an 89 325is with factory stereo, factory wiring, antenna, and amplifier.

I just installed the head unit and on occasion, it works perfectly, radio, tape player, everything.

However, unannounced, it will completely cut out and is substituted with a deafening sound of interference coming out of every speaker.

Like i said, sometimes it works, sometimes it doesn't. Is this a function of the radio itself or the amplifier?

I am very sure I wired it all up correctly and I soldered all connections.

Can you help me identify the cause? Thanks a lot!

[Garageaholic]

Well, I waited an hour and tried again and it works fine. I don't think it's the amp. I think it's either the radio or the antenna grounding perhaps? this is a god awful deafening loud sound and it's unpredictable. Has anybody else had this?

[Swanny]

Pm the one they call Luke? Seems like he has his audio know how on ice cold lock....

When I did the last stereo I bypassed the factory amp. Your guess about the grounding does seem pretty accurate to make that much noise at random though.

[Garageaholic]

Thank swanny

Does anybody else have a clue? Ill try to instigate this failure mode again and then disconnect the antenna to see if this feedback is coming from there.

[Cabriolet]

sounds like you are over heating the amp. i had that happen when i grounded it wrong. my rear left chnl got shorted to body and that same issue happened to me.

[German Audio Specialties]

Frank, here is a general rule: if you can change the volume of whatever racket you are having using the volume control, it is the deck. If the racket cannot be changed by the volume knob, it is likely the amp.

This is not in any way 100% guaranteed, but it is a starting point.

An easy way to test this is to pull the deck and use any old speaker (well, a working one, that is) directly connected to the deck.

Make sense?

Luke

[Garageaholic]

I will try that once I am able to witness it again and will report back to tie the loop on the issue. Thanks for the leads guys. That's all I could ask for!

[German Audio Specialties]

Updates, Frank?

[Garageaholic]

I have not heard the sound since it happened. I am unsure about the root cause, but I checked all wiring and grounds. I have a feeling that the electrolytic caps in the head unit are starting to hit the bucket.

I will keep you all updated as I progress!

[Tremelune]

Same issue here. I have a '90 M3 with the late-model factory stereo in it (4-channel Alpine CM5908 "Pyramid") and it behaves just as you describe. Is this your head unit? Did you get any further with your diagnosis?

My next move was to pull mine out of the car and wire it up in isolation, but I don't have the code and I don't think you can get the code for a radio this old...I was going to try this jumpering technique, but the website is sketchy. Anyone ever tried this?

http://rdecode.proboards.com/index.cgi?board=alpinecaraudiodecoding&action=print&thread=1948

[jeffw]

you can get the deck codes from bmw as long as you have the vin number for the car that the deck came out of

[Garageaholic]

Bad head unit. Switched it out and it works fine.