1989 Radio Ground?
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Instructor
Joined: Mar 2017
Posts: 223
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From: Ijamsville Maryland
1989 Radio Ground?
My newly acquired low miles 1989 with the Bose system clearly has a ground issue as the the radio whines/hums with background noise as soon as the unit is powered on. I know the PO spent a few dollars getting mouse damaged wiring repaired behind the dash as I have invoices for the repairs. My guess is that the radio head unit was not properly grounded when it was removed/reinstalled to access the problematic wiring. Can anyone provide a schematic or exploded view of the wiring harness for the radio head unit? I have the factory service manual, but it not like the C3 AIM with exploded views. Power antenna and all other electronis function as designed. I'm thinking that it may have just been the radio harness that was damaged and I'm hoping it's a plug and play affair with a bad ground. Any help is appreciated.
Pro
Joined: Sep 2008
Posts: 694
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From: St James New York
My newly acquired low miles 1989 with the Bose system clearly has a ground issue as the the radio whines/hums with background noise as soon as the unit is powered on. I know the PO spent a few dollars getting mouse damaged wiring repaired behind the dash as I have invoices for the repairs. My guess is that the radio head unit was not properly grounded when it was removed/reinstalled to access the problematic wiring. Can anyone provide a schematic or exploded view of the wiring harness for the radio head unit? I have the factory service manual, but it not like the C3 AIM with exploded views. Power antenna and all other electronis function as designed. I'm thinking that it may have just been the radio harness that was damaged and I'm hoping it's a plug and play affair with a bad ground. Any help is appreciated.
It's very likely the capacitors in the built-in amps found in your Bose speakers are shot and need to be replaced. Very common issue for the 27 yr old Bose speakers w/built in amplifiers. The whine/hum you hear is usually just that, not a ground problem.
Check out these links/threads for more info;
https://www.corvetteforum.com/forums...-speakers.html
http://carstereohelp.com/corvette.htm
https://www.corvetteforum.com/forums...f-speaker.html
https://www.corvetteforum.com/forums...mps-worth.html
Last edited by mako41; Jun 5, 2017 at 07:12 PM.
Pro
Joined: Sep 2008
Posts: 694
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From: St James New York
If the whine is produced at ALL speakers, it is not likely that all FOUR amps are faulty. The noise is coming from another source. If the pitch of the whine changes with engine RPM the alternator could be the source of the noise.
The antenna wire has an outer jacket / shield. This shield is joined to the antenna base at the rear of the car, and the antenna mounts into a wide conductive "ground plane" bonded into the rear body panel. The antenna also has a braided ground strap to the frame.
To answer your question: The antenna circuit and bonding system is probably the most significant "ground" involved for the radio, and with noise in the sound system.
The antenna wire has an outer jacket / shield. This shield is joined to the antenna base at the rear of the car, and the antenna mounts into a wide conductive "ground plane" bonded into the rear body panel. The antenna also has a braided ground strap to the frame.
To answer your question: The antenna circuit and bonding system is probably the most significant "ground" involved for the radio, and with noise in the sound system.
I do, and I had the exact same problem as the OP!
At first I thought it was a "ground" problem but my sound system grounds including the antenna grounds were all fine.
Yes ALL FOUR built in speaker amps were shot, this shouldn't be a surprise as it's a very common problem with 25year old Bose amps, after they were rebuilt with new capacitors all the hum and whine I was experiencing went away.
Last edited by mako41; Jun 5, 2017 at 11:42 PM.
Racer
Joined: Jul 2014
Posts: 266
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From: Philadelphia Pa
I have since developed a test for the speakers and amps that can be run by removing the radio and driving the speaker inputs with an aux device like an iPod or phone that has a headphone output. It takes about 20 minutes to get the radio out and run the test. Quite a bit longer to get the speaker out of the door in an 84-89. If the OP is interested, I'll share the how-to with him via PM.
I have intermittent sound from all 4. It seems like a grounding issue to me.
Edit: my antenna runner is shot so it only goes down 3/4 of the way. Not sure if that matters at all but it's on the to-replace list.
@OP sorry for the thread hijack! lol
Pro
Joined: Sep 2008
Posts: 694
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From: St James New York
yes i do have a bose. In a 1985 that i've owned since new. 32 years, and the 4 amps are still functioning properly. I went through this a few months ago. My symptoms were slightly different, in that i had no sound from two speakers, not "noise".
Not only are your symptoms different, but so is the Bose system you have in your '85, it's not the same as an '89 Bose setup! The amps may be similar but are not the same!
i followed the "wisdom" of people like you that always assume the amplifiers are the cause of bose system problems. (there are other causes of system problems, like the radio head itself.) i took my door apart (on an ncrs car that had never had the door panel off before) to get to the amplifier, and there was nothing wrong with it. I wasted a lot of time, and took my car apart when i didn't need to. It was the radio!
My wisdom is from the been there done that variety. You sound angry you wasted your time removing speaker amps that you say were fine.... Next time research and diagnose the issue properly and you won't waste that valuable time of yours. Don't vent on me or anyone else because you screwed up!
So anyway, people like you that only assume, lead people like myself and the op up the wrong path wasting time and money on something that may not be the cause.
Why is it that I'm assuming it's an in speaker amp problem but your not ASSuming when you say it's a ground issue?? Why is my potential solution to the OP's issues wasting his time and money on something that may not be the cause, but your potential solution isn't "wasting his time or money"?
You must be smarter than everyone else! Or maybe you just think you are!
I have since developed a test for the speakers and amps that can be run by removing the radio and driving the speaker inputs with an aux device like an ipod or phone that has a headphone output. It takes about 20 minutes to get the radio out and run the test. Quite a bit longer to get the speaker out of the door in an 84-89. If the op is interested, i'll share the how-to with him via pm.
Not only are your symptoms different, but so is the Bose system you have in your '85, it's not the same as an '89 Bose setup! The amps may be similar but are not the same!
i followed the "wisdom" of people like you that always assume the amplifiers are the cause of bose system problems. (there are other causes of system problems, like the radio head itself.) i took my door apart (on an ncrs car that had never had the door panel off before) to get to the amplifier, and there was nothing wrong with it. I wasted a lot of time, and took my car apart when i didn't need to. It was the radio!
My wisdom is from the been there done that variety. You sound angry you wasted your time removing speaker amps that you say were fine.... Next time research and diagnose the issue properly and you won't waste that valuable time of yours. Don't vent on me or anyone else because you screwed up!
So anyway, people like you that only assume, lead people like myself and the op up the wrong path wasting time and money on something that may not be the cause.
Why is it that I'm assuming it's an in speaker amp problem but your not ASSuming when you say it's a ground issue?? Why is my potential solution to the OP's issues wasting his time and money on something that may not be the cause, but your potential solution isn't "wasting his time or money"?
You must be smarter than everyone else! Or maybe you just think you are!
I have since developed a test for the speakers and amps that can be run by removing the radio and driving the speaker inputs with an aux device like an ipod or phone that has a headphone output. It takes about 20 minutes to get the radio out and run the test. Quite a bit longer to get the speaker out of the door in an 84-89. If the op is interested, i'll share the how-to with him via pm.
I speak from 1st hand experience! With a Bose equipped '89, same as the OP!
Shot! Yes all four of them! Just like the faulty amps dozens of other members of this forum found in their Bose equipped C4's who pointed out my potential problem and it's solution.
My wisdom on this issue was found on this forum....Years ago!
No ground problem at all!
Been there, done that with a Bose equipped '89!!.... Which is different than your '85 Bose setup.
After 25 years shot in-speaker amp capacitors in a Bose system is virtually a guarantee!
Last edited by mako41; Jun 9, 2017 at 12:06 AM.
Melting Slicks
Joined: Jan 2014
Posts: 2,478
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From: Downers Grove Illinois
Here is a good guide regarding Bose system repairs. As another data point my '92 spent most of its life in a climate controlled hanger and I still have had numerous leaking caps in the Bose speaker amplifiers. At least my front speakers aren't too bad to get to. I had replaced the head unit and CDM with a nice double DIN receiver and when I turned it on thought that it was bad because one speaker made no noise and the other hummed and was distorted. I pulled the speakers/amps and found all 4 had some level of electrolytic capacitor leakage.
Pro
Joined: Sep 2008
Posts: 694
Likes: 27
From: St James New York
Here is a good guide regarding Bose system repairs. As another data point my '92 spent most of its life in a climate controlled hanger and I still have had numerous leaking caps in the Bose speaker amplifiers. At least my front speakers aren't too bad to get to. I had replaced the head unit and CDM with a nice double DIN receiver and when I turned it on thought that it was bad because one speaker made no noise and the other hummed and was distorted. I pulled the speakers/amps and found all 4 had some level of electrolytic capacitor leakage.
If you dive into the links I provided above you'll see I posted this exact same link to a very extensive Bose Corvette amp/speaker repair guide.
