biker
Poster
Posts: 55
Reg: 12-25-23
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11-13-24 09:11 AM - Post#2875560
Hi guys. 91 K2500, original AM FM stereo with tape deck, no EQ.
CDM is #16141203.
The issue I have is intermittent radio reception. All antenna cables and connections are in good shape visually.
I have taken out and cleaned/inspected the CDM for bad solder joints etc.
All controls on the stereo function properly.
I noticed by accident that the reception will work when I turn on the headlights... so, I'm thinking some type of ground issue?
Anyone else experience this?
Thanks,
Brent.
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 Magnetocheck
"3rd Year" Silver Supporting Member
Posts: 539
Age: 70
Loc: Charlotte, NC, USA
Reg: 09-05-22
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11-13-24 05:21 PM - Post#2875572
In response to biker
Does the music drop out with the tape deck? If so , yeah probably a bad ground. You can always cobble up a new ground wire from the stereo case to a metal dash component if you’ve got room to work under there. What kind of aerial is on that 2500?
Bob
'65 Impala SS 396 Convertible
Member, National Impala Association
--It's weird being the same age as old people! |
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-13-24 08:21 PM - Post#2875577
In response to Magnetocheck
Thanks Bob. Plenty of room to wedge myself under and do some extra grounds. The antenna is a factory fender mount with the typical wire and connector in the fender.
This was a farm truck with so much mud and dust...I'm hesitant to try the tape deck without peeling it apart and cleaning it first.
I read tonight that unplugging the deck from the cdm may help, so I will try that before I install extra grounds.
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-18-24 04:37 PM - Post#2875734
In response to biker
Update:
Extra grounds made no difference. Disconnecting antenna cable and using a makeshift one didnt help
It's very clearly an issue internal to the cdm. I also discovered that toggling between am and fm will bring fm reception back.
I'd guess if the receiver portion has a voltage supply, its intermittent.
May cut my losses with the factory stuff and go with the retro sound unit that sits in the factory spot.
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Magnetocheck
"3rd Year" Silver Supporting Member
Posts: 539
Age: 70
Loc: Charlotte, NC, USA
Reg: 09-05-22
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11-18-24 05:46 PM - Post#2875739
In response to biker
 Agree- probably not worth messing with, unless you want the stock unit for appearance’s sake. If you do there are guys who will rebuild them for you , but I’ve never had it done.
Bob
'65 Impala SS 396 Convertible
Member, National Impala Association
--It's weird being the same age as old people! |
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-18-24 06:56 PM - Post#2875744
In response to Magnetocheck
Sigh, yes. I would like to leave it stock, but these components simply have a lifespan...
The retrosound unit actually looks pretty close to stock and has nice features.
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 someotherguy
Senior Moderator
Posts: 29818
Loc: Texas
Reg: 08-01-03
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11-20-24 06:06 AM - Post#2875816
In response to biker
About all that seems to go wrong in the CDM can happen to any old electronics, and that's failure of the electrolytic capacitors. Anyone that is halfway decent at electronics soldering work can replace them pretty inexpensively and easily.
I've done a lot of aftermarket stereos in my vehicles over the years but on my current project (the '93 C3500) I just said heck with it and put in a working used unit. The tape player is non-functional but I'm OK with that; no need for tapes anymore - I'm just going to hack the input from it for a bluetooth receiver module.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
Edited by someotherguy on 11-20-24 06:07 AM. Reason for edit: No reason given.
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-20-24 11:31 AM - Post#2875825
In response to someotherguy
Thanks Richard. I can handle soldering caps in, and really, I dont want to give up on it. If I can get the CDM to work reliably, I wont mind spending a few bucks on compatible speakers and possibly doing the same as you and adding an aux input.
My setup has a tape player, but no eq and manual hvac controls (no ac).
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someotherguy
Senior Moderator
Posts: 29818
Loc: Texas
Reg: 08-01-03
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11-20-24 10:41 PM - Post#2875837
In response to biker
I grabbed these pictures just a few minutes ago for a similar post in a different forum. This is the old CDM from my '93 with the am/fm/cassette, no EQ.
The cap with the domed top has failed; they should be flat. You can also see the leakage around it and the corrosion it's caused. The amplifier IC has a couple crusty looking legs. Then a smaller green cap is apparently also leaking or the board has a burnt spot, can't tell without further cleanup.
Since I already had a line on a working unit with EQ, I just swapped the whole thing out.
Richard
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-21-24 08:38 AM - Post#2875845
In response to someotherguy
Excellent shots Richard, thanks for this. Ok, I'm going to pull it apart and see what I can find.
I did look at my board when I had it apart to clean, but I thought a bad cap would be way more obvious. Your pics give me something to look for now.
They should be labeled so that I can find proper replacements?
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someotherguy
Senior Moderator
Posts: 29818
Loc: Texas
Reg: 08-01-03
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11-21-24 09:29 AM - Post#2875847
In response to biker
Yep, the label will indicate several characteristics, some of which you can 'fudge' and some you cannot.
The uF (microfarad) rating, which you should try your best to match exactly. There may be some fudge area for higher/lower but without understanding the circuit and the cap's role in it, you can get unexpected/bad results if you don't match the uF rating exactly.
Temperature range, which you can safely exceed without worry. Just don't go under. Automotive application caps need to be able to operate under fairly high temps.
Voltage rating. Same as temperature. You can exceed it, but don't go under. It's just the max voltage the cap is rated to operate at.
Polarity. Most electrolytic caps are polarized and must be installed in the correct orientation or you'll damage them. The negative terminal will be indicated by a band on the label, and often the circuit board is marked as well, but taking pictures ahead of time to reference later is recommended.
There's literal tons of info out on the web to help understand these things but that should be enough to get you on target.
Example pic of electrolytic cap markings, this is a 2200uF (microfarad) cap with a max operating voltage of 16V, temperature range of -40 to +85° C, and you can see the band indicating the negative terminal, which on a new cap is always the shorter one. Of course once you solder it in you'll trim the excess leads off.
Richard
 Attachment: cap.jpg (19.78 KB) 23 View(s)
| 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 / 93 C3500 dually |
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biker
Poster
Posts: 55
Reg: 12-25-23
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11-21-24 12:50 PM - Post#2875850
In response to someotherguy
Thank you sir! Agreed. This gets me enough info that I can research and get the proper caps. I'm looking forward to this.
I'm on a roll...repaired a door micro switch in my microwave today.
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