Radio static and alternator noise through radio.

[denverkenyon99]

1990 Chevy K1500
My issue is mostly stated in this thread:

Radio volume

My radio makes a humming noise and gets louder the more throttle i give, then my volume won’t go higher then 3 it hits 3 and restarts, but if i have a cassette in the humming goes away and volume is fine, stick radio. Thanks

www.gmt400.com

Basically, constant static and alternator noise through the radio when it is on, but none when off. Makes a static click when I turn it on and off.

The person in the link I provided asked the question “where might the ground be that might be bad” and I have that same question as “bad ground” seems to be the common fix, other than replacing the radio for an aftermarket.

That brings me to my next question. If I get an aftermarket dash radio that sits below the center vents, will the stock radio still have all of its functionality? I don’t want to add anything that will only make more problems. The center cassette player was missing when I got the truck, and there are only 2 wires going to that area. A yellow and a gray. I don’t see where anything else could plug in.

 

[Drunkcanuk]

You most certainly have a ground issue. As for where exactly they are, sorry, can't be of help there, hopefully others can narrow down the location for you.

In the engine and performance section there is a sticky section. There are factory service manuals there that will have wiring diagrams.

As for the radio. If you add an aftermarket stereo, the radio will be redundant anyway.
There are 3 parts to the factory system. The radio part, the cassette player and the computer deal up under the dash, to the right of the steering wheel. A silver box, last I remember, about 1"x6"x8". It's the brain of the system.
Id you trace the wires from where the deck is supposed to be, they will plug into it.

I guess you could probably leave it in there, and wire up an aftermarket unit separately, maybe to keep the clock. Other than that, there is no point. Find a wiring harness online and toss a new deck in the dash.

Your issues can possibly be coming from the computer box thing, they are known to go bad.

Good luck and hopefully this helps a bit

 

[movietvet]

Look at my Garage or Audio/Electronics thread about my girl's Retro Radio install in her 1990 K2500.

Do a search for "Retro Radio" and it will come up.

If you end up doing the Retro Radio, you will want to remove that controller, up in the dash. It is behind and to the passenger side of the back of radio. It will come out pretty easy. Couple of mount brackets to deal with. The smaller controller I received with the new Retro Radio, has some "L" shaped brackets and you can mount the controller to it and attach at the firewall. Kind of a PITA but doable. I reused the speaker wires and speakers at the front and she is happy. The wires are supplied for the rear speakers but she was ok with not hooking them up. I just left the equalizer/cassette in the dash to cover up the hole but it does not do anything. I looked and looked and found at this site and others that the old systems are just not gonna last over a 34 year period. You can get working used or "rebuilt" at ebay but I did not trust them. The Retro Radio looks close to stock and does a great job for her.

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[AK49BWL]

You will need to duplicate the wiring for the aftermarket radio, that's the only way you're keeping stock radio functionality with an aftermarket installed - and you'll have to figure out how the speakers are going to be wired because they cannot be connected to both decks simultaneously. The alternator hum issue could be a bad ground, but at this point in the game I would sooner say the input power filter capacitor has gone south in the CDM.

The other issue in the thread you linked, with the volume control, you can take the head unit apart and clean the buttons and their contacts. Contact cleaner sprayed in from outside likely won't do much because the actual button electrical contacts are under a layer of rubber.

Be very careful and have the head unit face down when taking it apart - the early heads have a load of springs behind the buttons that will disappear in an instant. Disassembly and Reassembly works best with the unit face down.

The two wires behind where the tape deck should be in the dash would go to the tape deck's 5-band EQ. The tape deck itself contains its own harness that plugs into the CDM.

 

[John DeWitt]

If this has been resolved, then disregard. It was just listed as a "similar thread" & the title/issue is up my area of expertise. Although typically yes, it can be a ground issue it's not always necessarily an "electrical" ground problem but an EFI/RFI issue.....but sometimes ground bonding can fix the issue. 1st, you need to determine if the interference is coming in through the powerline side or the antenna side. Use the process of eliminating by unplugging the antenna from the rear port & tuning through the FM & AM band while listening to see if the issue is still present. If it is, it's powerline side. If not, it's antenna side. Although bonding can help, it may not eliminate the bleedthrough (there is a difference between an Electrical Ground & RF ground). Power side, you can install snap on ferrite chokes to help filter off noise, antenna side RF bonding or possibly be looking at having to replace the antenna coax if it's detiorated.

Too add in this edit, it is possible there are failing components in the radio itself. Likely in the Audio or RF amplifier circuitry.

 

[Cadillacmak]

If this has been resolved, then disregard. It was just listed as a "similar thread" & the title/issue is up my area of expertise. Although typically yes, it can be a ground issue it's not always necessarily an "electrical" ground problem but an EFI/RFI issue.....but sometimes ground bonding can fix the issue. 1st, you need to determine if the interference is coming in through the powerline side or the antenna side. Use the process of eliminating by unplugging the antenna from the rear port & tuning through the FM & AM band while listening to see if the issue is still present. If it is, it's powerline side. If not, it's antenna side. Although bonding can help, it may not eliminate the bleedthrough (there is a difference between an Electrical Ground & RF ground). Power side, you can install snap on ferrite chokes to help filter off noise, antenna side RF bonding or possibly be looking at having to replace the antenna coax if it's detiorated.

Too add in this edit, it is possible there are failing components in the radio itself. Likely in the Audio or RF amplifier circuitry.

John said it perfect, alternators, motors, spark, can all create Radio Frequency (RF) and that can travel over any electrical or though the air. Sometimes you just need an RF choke.

 

[John DeWitt]

John said it perfect, alternators, motors, spark, can all create Radio Frequency (RF) and that can travel over any electrical or though the air. Sometimes you just need an RF choke.

Thank you sir. Too add, I have seen many times where one thinks it's alternator noise due to the increase in whine matching the rpm of the engine when in fact its occasionally been the fuel pump. Sometimes adding some ferrite chokes or inline filter is just easier than trying to bond/shield every frigin component that creates the unwanted noise.