Radio Capacitors for logic circuit

[4300Dakota]

I wanted to post this thread to help someone else with their radio issues (if they are the same ones I dealt with).
The symptoms: volume buttons would not work, tuning buttons would not work, the presets would not work, clock was stuck on 1:00 with no way to set because those buttons did not work. But all speakers worked and there was sound coming out.

The logic circuit is the orange and green circled capacitors, the violet circled capacitors feed the logic circuit, the blue capacitor stabilizes the board input (not necessary, but a good idea)
I changed the small green ones to ceramic, will be much more robust. Physical dimensions of the capacitors are also crucial to keep in mind, and all of these fit.

Green: 6qty; initially: Radial 1uF-5V-electrolytic ; what I put in: Radial-1uF-X7R-50V-ceramic
Orange: 4qty; initially: Axial 100uF-16V-electrolytic ; what I put in: Axial 100uF-25V-electrolytic
Violet: 3qty; Initially: Radial 470uF-16V-electrolytic ; What I put in: Radial 470uF-16V-electrolytic
Blue: 1qty; Initially: Radial 4000uF-16V-electrolytic ; What I put in: Radial 4000uF-35V-electrolytic

Green: KEMET C330C105K5R5TA
Orange: Vishay TE1211-E3
Violet: Knowles / Cornell Dubilier SEK471M016ST
Blue: Chemi Con ELBG350ELL402ALP1S

I thought that instead of replacing every capacitor, if your symptoms are similar to the ones I encountered on my radio (and you don't have any visibly ruptured capacitors), then this is worth a try. Also note that this board is from a 1989 and this radio board gets changed later on after early 1990s. So, the board looks different and uses slightly different circuitry. Hope this helps someone!

​

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[H2814D]

I wanted to post this thread to help someone else with their radio issues (if they are the same ones I dealt with).
The symptoms: volume buttons would not work, tuning buttons would not work, the presets would not work, clock was stuck on 1:00 with no way to set because those buttons did not work. But all speakers worked and there was sound coming out.

The logic circuit is the orange and green circled capacitors, the violet circled capacitors feed the logic circuit, the blue capacitor stabilizes the board input (not necessary, but a good idea)
I changed the small green ones to ceramic, will be much more robust. Physical dimensions of the capacitors are also crucial to keep in mind, and all of these fit.

Green: 6qty; initially: Radial 1uF-5V-electrolytic ; what I put in: Radial-1uF-X7R-50V-ceramic
Orange: 4qty; initially: Axial 100uF-16V-electrolytic ; what I put in: Axial 100uF-25V-electrolytic
Violet: 3qty; Initially: Radial 470uF-16V-electrolytic ; What I put in: Radial 470uF-16V-electrolytic
Blue: 1qty; Initially: Radial 4000uF-16V-electrolytic ; What I put in: Radial 4000uF-35V-electrolytic

Green: KEMET C330C105K5R5TA
Orange: Vishay TE1211-E3
Violet: Knowles / Cornell Dubilier SEK471M016ST
Blue: Chemi Con ELBG350ELL402ALP1S

I thought that instead of replacing every capacitor, if your symptoms are similar to the ones I encountered on my radio (and you don't have any visibly ruptured capacitors), then this is worth a try. Also note that this board is from a 1989 and this radio board gets changed later on after early 1990s. So, the board looks different and uses slightly different circuitry. Hope this helps someone!

​

You must be registered for see images attach

There are quite a few of us with the updated, later model CDM's that have the 1:00/98.1 issues. Of course the circuit boards are quite different on them and the replacement of the caps on the later ones has not always been successful. Your CDM has so many caps on the various circuit boards, that the probability of the majority of the other electrolytic caps have likely come to the ends of their useful lives. Just curious as to whether or not you checked the rest of them, at least with an ESR Meter?

If I was going to continue to use that CDM, and in order to prevent problems later, I would replace ALL of those caps on both boards with new ones, and there are a lot of them, so it would involve some time. The reason I say that is because there are caps on that board, that once they fail, they will take out the output chips, which are no longer available unless you can salvage them off of other boards that have not already gone bad. The repair facilities will no longer even attempt repairs on these older ones.

I have a couple of those older ones sitting here that I haven't even messed with yet, but I don't remember what the issues were with them right now. Now I'm curious again, since I've also been messing with my original 16169561 lately trying to figure it out.

But in any case, it is good you came back with this info.

 

[4300Dakota]

Very good inputs. Losing those chips would make the boards essentially trash. Larger electrolytic caps "usually show external wear", but obviously not always. Everything on the power board tested good, as well as the 4000uF tested good (I replaced that just to ensure a smooth board signal). The bad caps were the small 1uF 5V caps. And I agree that the only true "fix" would be to replace all of the caps, including the power board. My power amp worked fine. After doing this, everything works perfectly. I didn't want to spend money on unnecessary parts or the time if need be.

 

[Bert_]

I was under the impression that the orange and green circled areas was the audio section. The chips with the thermal paste are the amps. I have replaced those capacitors on several GM radios that exhibited audio problems.

 

[someotherguy]

Interesting dual-board CDM? I don't think I've opened one of those up, only the later single board style with the big heat sinks on the amps mounted at the edge.

Whether to replace old caps is a pretty good debate. While on one hand you could say, caps are fairly cheap, and there's not a whole lot of them in there - it just makes sense to replace them all "while you're there" ... and often in other scenarios, that's exactly what I've done, because it made sense. In the world of old arcade game monitors, by the time we'd get hold of them as collectors, multiple caps would be bad, causing various issues. So the practice was just to replace essentially all of them.

There's others that subscribe to the practice of, if it ain't broke, don't fix it - and testing the various caps to only replace what is necessary. Less work on the boards means less chance of causing new problems (lifted traces, installing defective new components, installation error - polarity mistakes go boom!)

Richard

 

[H2814D]

Interesting dual-board CDM? I don't think I've opened one of those up, only the later single board style with the big heat sinks on the amps mounted at the edge.

Whether to replace old caps is a pretty good debate. While on one hand you could say, caps are fairly cheap, and there's not a whole lot of them in there - it just makes sense to replace them all "while you're there" ... and often in other scenarios, that's exactly what I've done, because it made sense. In the world of old arcade game monitors, by the time we'd get hold of them as collectors, multiple caps would be bad, causing various issues. So the practice was just to replace essentially all of them.

There's others that subscribe to the practice of, if it ain't broke, don't fix it - and testing the various caps to only replace what is necessary. Less work on the boards means less chance of causing new problems (lifted traces, installing defective new components, installation error - polarity mistakes go boom!)

Richard

Here is a picture of a dual circuit board CDM similar to the original commenters. They were installed in the older vehicles around 1989, or so, before the much better and higher output CDM's started getting used later on. I just counted 40 e-caps total for both boards, so it would definitely involve some work replacing all of them. My fear, though, is risking a failed output chip due to a failed e-cap later, if I was finally able to get my CDM to operate correctly. At a minimum I would check the remaining installed caps with an ESR Meter just to confirm they hadn't risen too high in resistance. One benefit of most all of our CDM's, even the older ones, is that they all used the same molex connections for the speakers, power supplies, and head unit.

 

[someotherguy]

Here is a picture of a dual circuit board CDM similar to the original commenters. They were installed in the older vehicles around 1989, or so, before the much better and higher output CDM's started getting used later on. I just counted 40 e-caps total for both boards, so it would definitely involve some work replacing all of them. My fear, though, is risking a failed output chip due to a failed e-cap later, if I was finally able to get my CDM to operate correctly. At a minimum I would check the remaining installed caps with an ESR Meter just to confirm they hadn't risen too high in resistance. One benefit of most all of our CDM's, even the older ones, is that they all used the same molex connections for the speakers, power supplies, and head unit.

oof.. big thumbs down on that one! I'll pass. Glad I got the "easier" ones!

Richard

 

[Bert_]

That's the style that is in my '93. Suppose it could be a replacement though

 

[cc333]

This reminds me that I still need to recap my (presumably factory original) '94 unit. It works and sounds OK, but the tuner is weird (it doesn't filter out adjacent AM frequencies very well, so if I'm listening to something on, say, either 730 or 750 and there's a strong signal on 740, I'll here that strong signal spilling over onto 750 as well as 730, which I'm pretty sure isn't normally how this tuner should work).

c

 

[someotherguy]

This reminds me that I still need to recap my (presumably factory original) '94 unit. It works and sounds OK, but the tuner is weird (it doesn't filter out adjacent AM frequencies very well, so if I'm listening to something on, say, either 730 or 750 and there's a strong signal on 740, I'll here that strong signal spilling over onto 750 as well as 730, which I'm pretty sure isn't normally how this tuner should work).

c

Those caps in the tuner section are really tricky since they have to live under the metal cover. Be sure you don't go wild with the voltage difference like I did, and had to lay that one big cap over sideways, LOL

Richard

 

[cc333]

Those caps in the tuner section are really tricky since they have to live under the metal cover. Be sure you don't go wild with the voltage difference like I did, and had to lay that one big cap over sideways, LOL

Yeah, I sort of remember that from when this subject last came up.

I think bumping up the voltage a bit would be good for longevity, but the more important feature, I think, is temperature rating. Most common capacitors come rated for either 85º or 105º, and the 105º-reated capacitors tend to last a bit longer in hot environments, such as the cab of a hot truck.

I'm debating whether I should find another '94 CDM and recap that first so I don't have to leave the truck radio-less while I recap the original. Used but working CDMs aren't too easy or cheap to find though, are they?

c

 

[someotherguy]

Yeah, I sort of remember that from when this subject last came up.

I think bumping up the voltage a bit would be good for longevity, but the more important feature, I think, is temperature rating. Most common capacitors come rated for either 85º or 105º, and the 105º-reated capacitors tend to last a bit longer in hot environments, such as the cab of a hot truck.

I'm debating whether I should find another '94 CDM and recap that first so I don't have to leave the truck radio-less while I recap the original. Used but working CDMs aren't too easy or cheap to find though, are they?

c

The recap on that style just being 9 caps won't take you long. I think it took me about an hour and that included taking pics of the original caps so I wouldn't lose track of the polarity on them, and adding the bluetooth module and wires. That later style CDM has a tricky one or two; in particular I recall one of the two stuck by the glue around the large square Motorola surface mount IC having a diagonal spread-leg orientation that made it a little tough to determine where on the back side to de-solder - the one to the right of that chip if you're looking at it with the chip markings upright.

Richard

 

[Cadillacmak]

I have a 89 that the radio all works, no sound from the speakers, and if you hit the volume button up it goes to 1, if you press up and down it goes to three.
Is this internal or shorted speakers?
I will try and do more tests Thursday but the service manual does not mention this problem.

 

[Bert_]

I have a 89 that the radio all works, no sound from the speakers, and if you hit the volume button up it goes to 1, if you press up and down it goes to three.
Is this internal or shorted speakers?
I will try and do more tests Thursday but the service manual does not mention this problem.

It's been a while since I've seen a stock radio that didn't have some sort of problem. All that I have seen has been dead capacitors in the amp section and/or the tuner section.

 

[H2814D]

I have a 89 that the radio all works, no sound from the speakers, and if you hit the volume button up it goes to 1, if you press up and down it goes to three.
Is this internal or shorted speakers?
I will try and do more tests Thursday but the service manual does not mention this problem.

Don't quite understand. You say "the radio all works," but then "no sound from the speakers." Are you troubleshooting the radio or the speakers, or both?

That "89" likely is one with close to 40 capacitors in it that the majority of those caps have reached and surpassed their useful lives. The problem with those older models is that once the caps start going bad they take out the output IC's, and those parts are no longer available unless you can salvage them off of another radio. The repair shops have given up on those multi-layer circuit board CDM's.

 

[Cadillacmak]

Don't quite understand. You say "the radio all works," but then "no sound from the speakers." Are you troubleshooting the radio or the speakers, or both?

That "89" likely is one with close to 40 capacitors in it that the majority of those caps have reached and surpassed their useful lives. The problem with those older models is that once the caps start going bad they take out the output IC's, and those parts are no longer available unless you can salvage them off of another radio. The repair shops have given up on those multi-layer circuit board CDM's.

All the buttons on the radio works but the volume, I had my suspicions that a speaker failure is the cause of this due to a separate unit acting the exact same when I plugged it in. I am going to trouble shoot everything I can tomorrow, but research on here brought me to this thread and now I am wondering if capacitors are the problem.

 

[H2814D]

All the buttons on the radio works but the volume, I had my suspicions that a speaker failure is the cause of this due to a separate unit acting the exact same when I plugged it in. I am going to trouble shoot everything I can tomorrow, but research on here brought me to this thread and now I am wondering if capacitors are the problem.

The probability that the capacitors in your CDM are partly causing the issues you are describing is high, since the failures of them would certainly affect sound quality, circuit integrity, and stereo sound output. At this point, I would guarantee many of them are no longer working as they would. I'm sure you are aware of their importance.

The issue now though, is do you really want to go through all of the trouble and time it will cause you to replace them only to find out the output IC's have failed as well? The newer CDM's are much easier to work with and will improve the sound quality of your system, if you can ensure your speakers are good too. In many cases the newer CDM's will operate correctly with your other existing components, because the pinouts and the molex connectors did not change over the many years these CDM's were in use. Of course, check that to make sure though.