Speaker Whine, Possible Bad CDM?

[stafford0620]

I have a 94 Full Size blazer. It had an aftermarket JVC single din radio in it when I bought it. For a while now I've been wanting to use the stock radio to keep it original so today that's what I did. I went to the junk yard and bought the factory cassette player with no EQ adjustment out of a 94 suburban and a CDM out of a 91 Silverado. I get everything plugged back in and the radio works but I have a whine coming from the speakers. It starts off loud then quiets down some after a few seconds. Im wondering if the CDM is bad or if I have an issue somewhere else. Every speaker works. The front passenger side dash speaker has some static noises as well but is intermediate. All the radio controls work and so does the cassette player. I have the radio with the bass and treble adjustments and the manual cassette player with a small pocket on the right side. The speakers have been changed to Kicker 4x6's in the dash and 4x10's in the rear. Any advice helps.

 

[thegawd]

it's not a ground loop is it? does it change its pitch with the engine speed?

if so add another separate ground from a screw on the stereos chassis to the frame under the dash somewhere.

 

[stafford0620]

When you mean the stereos chassis are you talking about the CDM itself or the metal plate attached to the CDM?

 

[thegawd]

I dont even know what a cdm is but the same deal can be applied to any piece of 12V electronic equipment. so sure you could add a dedicated ground to anything really.

what happens is to many things are going through the same ground strap..... So by adding more grounds you eliminate that problem.

I couldnt figure this out for the longest time on my jvc car stereo in the garage and then again in my truck with a pioneer deck.... the truck ground loop drove me crazy and it stopped after doing 1 simple jumper from the cd deck chassis to the frame under the dash.

the grounds under the hood have all been updated to 4 gauge wire as they disintegrated into dust. consider these as well.

 

[stafford0620]

Update!

When I refer to CDM, I am talking about the brains of the radio under the dash next to the gas pedal. This controls the headunit and cassette player(its basically an amplifier). Its called that because of the number associated with the box. I believe its the part numbers. Anyways I first checked all my grounds and didn't notice anything out of the ordinary. I then added another ground from the CDM to the frame. No change. Today I had an alert that a 92 C1500 was just put out on the local pull a part. I quickly snagged the CDM at lunch and when I plugged it up it fixed all my issues. Thank you for your suggestions though. Very appreciative. Im glad to have 90's OEM sound again lol!

 

[thegawd]

PERFECT! if you ever have a whine that changes pitch with the engine that is a ground loop.

CHEERS!

 

[kennythewelder]

Update!

When I refer to CDM, I am talking about the brains of the radio under the dash next to the gas pedal. This controls the headunit and cassette player(its basically an amplifier). Its called that because of the number associated with the box. I believe its the part numbers. Anyways I first checked all my grounds and didn't notice anything out of the ordinary. I then added another ground from the CDM to the frame. No change. Today I had an alert that a 92 C1500 was just put out on the local pull a part. I quickly snagged the CDM at lunch and when I plugged it up it fixed all my issues. Thank you for your suggestions though. Very appreciative. Im glad to have 90's OEM sound again lol!

Glad you got it fixed. I really like how discripteve you are in your post. It helps a lot when reading your questions. I remember a long time ago, we would install what we called a bypass filter on the power wire that supplies the stereo. This would filter out engine static, ECT, from things like your ingition coil, spark plugs ECT. Most likely it was a similar filter type of thing, that shorted out or burned up inside the CDM as you call it. This filter, was maybe a resistor, or some similar thing, IDK for sure.

 

[kennythewelder]

It

PERFECT! if you ever have a whine that changes pitch with the engine that is a ground loop.

CHEERS!

It could have been on the ground side, I don't remember. It's been a long time.

 

[stafford0620]

Much appreciated @kennythewelder I'm was thinking about trying the bypass filter and did some research on these as well. I quickly eliminated it being alternator/engine noise due to the fact that the pitch never changed with RPM's and it would do the exact same thing when the truck was not running and just in the ON position or Accessories position with the key turned back. That's what led me to believe I had a bad component somewhere. I have also read on another forum that these CDM's has a factory noise filter capacitor. I'm gonna see if I can find the specific one and post about it since I have not found any information about that yet and it could solve a few peoples issues. I've done quite a bit of research about these units where I feel like I am an expert at this point lol!