88-94 Radio Issues

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phatphuck

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Calling on the obs savants.

My grandpa has two 88-94 early model gmt single cab c1500s. Both in great great shape but both experiencing the same issues with the factory radios.

Both of these are cassette/equalizer units and both power on, with some of the button functions working on the displays, but tune, seek, volume etc, buttons will not work and getting no sound at all from the speakers although the volume is reading at mid.

Am I looking at defective control module or what?

Did some looking around and not finding what I'm looking for so I put the question to ya'll.

Thanks! PP
 

TechNova

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Known problems with the control module down by the gas pedal. Get a bunch of spares from salvage yards. My local let's me test them at home and return of not working. There is supposed to be a filter capacitor that goes bad. A member here knew how to fix but I have not been able to contact him for the info. I took a couple boxes to a friend that used to work on electronics but he could not get them to act up. One was good and the other had an intermittant problem.
 

DerekTheGreat

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Also, open the donor box up and inspect the pins & wire traces right where the connector comes into the module. If corroded, they're trash. Look around on this forum, there is a good thread which outlines which units you want as some have better output and work better with aftermarket speakers.
 

Crytone

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As said, worth a shot to crack them open and take a look. Capacitors will either be leaking or bulging on top. They can also look fine but be bad too. When I repair electronics this old, I just replace the capacitors anyways even if they look fine.

Honestly, most older electronics have issues with capacitors. The older electrolytic caps leak as they age, and if left too long, will corrode the PCBs. Once it gets that bad that PCB traces are being destroyed, it's much more difficult to repair.

The fix, if some bad capacitors are the culprit, is to open them up, clean them and replace all the electrolytic capacitors. The EQ/tape deck, headunit and the brain under the dash all have capacitors in them. Worth checking the connectors and wiring too, as said.
 

Gary Mettus

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Capacitors will either be leaking or bulging on top. They can also look fine but be bad too. When I repair electronics this old, I just replace the capacitors anyways even if they look fine.

Honestly, most older electronics have issues with capacitors. The older electrolytic caps leak as they age, and if left too long, will corrode the PCBs. Once it gets that bad that PCB traces are being destroyed, it's much more difficult to repair.

No truer words have been written. People think solid state electronics need no maintenance but electrolytic capacitors definitely need to be replaced much sooner than 30 years especially if you want to maintain sound quality. They may work but the sound turns to crap. If you were to go to all the bother refurbishing the OEM radio you may as well yank it out and replace it with a new head unit where the cassette goes. Crutchfield has everything you need to do the conversion. The OEM speakers are an odd 9.5 ohm so you it would be best to replace those as well as most new head units are rated for 4 ohm speakers. I wanted to keep my Dad's truck as original as I could but there is no comparison between my new stereo and the old one. I had a engine speed dependent whine I could not get rid of. Best money and time I could have spent. I did keep all the old parts in a box just in case originality becomes more important than listening pleasure down the road.
 

Eveready

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It doesn't help that the caps in the factory radios are CHEAP. GM never expected those radios to be in use decades later. The good news is that replacement caps are also cheap and much more reliable. I didn't bother to fix mine and went with a mid mount aftermarket radio because I wanted the bluetooth phone capability.

There are places you can send the brain box to that will fix it and return it but from what I hear they are quite expensive. i would only do that if I was trying to do an "as new" restoration.
 
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Ken Bell

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Calling on the obs savants.

My grandpa has two 88-94 early model gmt single cab c1500s. Both in great great shape but both experiencing the same issues with the factory radios.

Both of these are cassette/equalizer units and both power on, with some of the button functions working on the displays, but tune, seek, volume etc, buttons will not work and getting no sound at all from the speakers although the volume is reading at mid.

Am I looking at defective control module or what?

Did some looking around and not finding what I'm looking for so I put the question to ya'll.

Thanks! PP
I have the exact same problem. Changed the CMD, but Eq still has some lights but not all of them, just the first and last.
 

DerekTheGreat

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I have the exact same problem. Changed the CMD, but Eq still has some lights but not all of them, just the first and last.
Like AK49 said, you put the wrong doofrad in there. Ya need to look into that thread to double check the model number against the one you're pulling or looking at on the interwebz.
 
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