C4 CDM Removal?
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
C4 CDM Removal?
As a new member I risk asking a question that has already been answered and posted. Please bear with me. I did search the forums but didn't find what I was looking for. I have a '91 Corvette Convertible and generally do all my own maintenance but I have to admit for some of the electrical issues I usually need help. The problem: the radio powers up and the antenna raises up, but out of the speakers is a loud squeal. The same is true for the CD player. So I've concluded that it is either the radio unit in the center of the dash or the CDM which in my car is under the passenger-side dash. So before I start dismantling the dash, I have two questions:
1. Could it be the CDM?
2. Can the CDM be accessed easier by removing the glove compartment?
Thank you, Dave D
1. Could it be the CDM?
2. Can the CDM be accessed easier by removing the glove compartment?
Thank you, Dave D
Last edited by ddischiave; Mar 10, 2021 at 03:27 PM. Reason: spelling
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
The bose speakers in these cars are notorious for failing capacitors, resulting in a number of symptoms including no sound, static, squealing, etc. So, while it could be the CDM or the Control unit, both of which are in the dash of a 91 (i believe), it could also be speakers. These may be easier to look at first. They certainly are more easily accessed than the other items.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
The bose speakers in these cars are notorious for failing capacitors, resulting in a number of symptoms including no sound, static, squealing, etc. So, while it could be the CDM or the Control unit, both of which are in the dash of a 91 (i believe), it could also be speakers. These may be easier to look at first. They certainly are more easily accessed than the other items.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
Please keep the suggestions coming ... I can use all the help I can get.
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
I have a couple of 93s, so my CDM is in the rear compartment behind the passenger seat. Much easier to get to! I just finished replacing all capacitors on my 4 amplifiers (each speaker has an amplifier). If you have a service manual, there are some diagnostic flow charts in the electrical section (search radio diagnosis if you have the CD) and find the one that says no sound out of speakers. There are several very good threads on this forum about the bose system so search that and read them. Also, on you tube there are some good videos, Mark's corvette has a 4 part series on the capacitors. There are a number of repair shops that various people on here will recommend. I have personally used Car Stereo Help and Bose Central, both located in Florida. Even if you use them, you will have to pull the offending unit/units.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
I have a couple of 93s, so my CDM is in the rear compartment behind the passenger seat. Much easier to get to! I just finished replacing all capacitors on my 4 amplifiers (each speaker has an amplifier). If you have a service manual, there are some diagnostic flow charts in the electrical section (search radio diagnosis if you have the CD) and find the one that says no sound out of speakers. There are several very good threads on this forum about the bose system so search that and read them. Also, on you tube there are some good videos, Mark's corvette has a 4 part series on the capacitors. There are a number of repair shops that various people on here will recommend. I have personally used Car Stereo Help and Bose Central, both located in Florida. Even if you use them, you will have to pull the offending unit/units.
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Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
The speakers are certainly easier to access. I suspect the speaker amps have the same capacitor issue as the CDM. It seems odd to me that all four speaker amps would ll fail at the same time.
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
Dave, on my 93s there is a relay that controls the feed to the speakers. If you can find that on yours, you should check it for proper operation (mine, of course, is in the rear storage compartment). If it is bad, that would cause all 4 speaker to not work. My rear hatch on the convertible did not work and it was the relay with a corroded connector. One thing you should ask on every problem on these cars is, "Could this be the result of a bad/corroded connector or ground". You will be surprised how many times the answer is YES.
I also meant to ask if the speakers were inop when you acquired the car. If so, they may not have all failed at the same time.
I also meant to ask if the speakers were inop when you acquired the car. If so, they may not have all failed at the same time.
Last edited by jrobin1; Mar 11, 2021 at 10:54 AM.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
Dave, on my 93s there is a relay that controls the feed to the speakers. If you can find that on yours, you should check it for proper operation (mine, of course, is in the rear storage compartment). If it is bad, that would cause all 4 speaker to not work. My rear hatch on the convertible did not work and it was the relay with a corroded connector. One thing you should ask on every problem on these cars is, "Could this be the result of a bad/corroded connector or ground". You will be surprised how many times the answer is YES.
I also meant to ask if the speakers were inop when you acquired the car. If so, they may not have all failed at the same time.
I also meant to ask if the speakers were inop when you acquired the car. If so, they may not have all failed at the same time.
I'm thinking about disconnecting one speaker at a time and if nothing changes reconnect it and move on to the next speaker etc in hopes that it is only one speaker. If after I sequence through all four speaakers and nothing changes then I'll see if I can access the CDM from the top by removing the glove compartment. If not, then try my hand at being Houdini by trying to reach it from under the dash ... I'm hoping I don't have to remove the passenger seat.
Racer
Joined: Jun 2019
Posts: 390
Likes: 126
From: Franklin, TN
That is a good approach. When I redid my capacitors recently I didn't ace the front passenger amp repair the first time and when I plugged them up, I got a real squeal out of it. I unplugged it and the other three worked fine. While you are at that connection, you should put a meter on the power and ground wires (there are 4 and 2 are the signal wires) and verify that you have power at the speaker (if not check the relay). Also, turn volume up high and put your ear real close to speaker to see if you hear anything at all.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
That is a good approach. When I redid my capacitors recently I didn't ace the front passenger amp repair the first time and when I plugged them up, I got a real squeal out of it. I unplugged it and the other three worked fine. While you are at that connection, you should put a meter on the power and ground wires (there are 4 and 2 are the signal wires) and verify that you have power at the speaker (if not check the relay). Also, turn volume up high and put your ear real close to speaker to see if you hear anything at all.
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
The CDM/Receiver is a bit of a PITA to get to. Removing the glove box doesn't help at all. Remove the under panel and the side panel. It's stacked to the right of the relays under the cruise control module behind the main fuse panel.
Thread Starter
Instructor
Joined: Mar 2021
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From: New York
Melting Slicks
Joined: Jul 1999
Posts: 3,214
Likes: 101
From: Decatur, Alabama
If your planning on keeping the car, get a FSM and bite the bullet and pull the CDM, if it don;t need it now, it will, and soon. Yes, there is a lot of stuff that needs to come off on the passenger dash, it can be done in under two hours, an hour if you have done it before.
Thread Starter
Instructor
Joined: Mar 2021
Posts: 113
Likes: 22
From: New York
If your planning on keeping the car, get a FSM and bite the bullet and pull the CDM, if it don;t need it now, it will, and soon. Yes, there is a lot of stuff that needs to come off on the passenger dash, it can be done in under two hours, an hour if you have done it before.