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GM300 audio issues

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bullseye1584

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I have just installed a GM300 in my 2004 Chevy pickup. When the vehicle is off and the radio is powered up the rx audio is fine. But, when the vehicle is started and running, the rx audio becomes distorted and I am unable to understand what is recieved. Anyone know what the problem could be? Thanks in advance.
 

cmdrwill

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Just a thought, GM300 radios can have a microphonic RX VCO that can sound like you describe.
 

12dbsinad

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Just a thought, GM300 radios can have a microphonic RX VCO that can sound like you describe.
This could possibly be it. GM300 are common to be microphonic caused by the interconnecting pins. Try giving the radio a good wack with the palm of our hand a few times on the top just behind where the front would split away from the radio and see if anything changes while the symptom is present. If it does or all of a sudden works fine, thats your issue.
 

jeepjunkie007

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Check where your antenna wire is ran as well. Ive had problems with mine if it is too close to a main power supply coming through the firewall, the reception is distorted from the alternator.
 

12dbsinad

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It sounds like the radio is inducing some sort of RF when the vehicle is running either through the DC power or the antenna. Does it just do it a particular frequency or all of them? If there is more than one programmed. A couple things to try, first try powering the radio with a jump pack inside the cab instead of the vehicle battery. See if anything changes. Second, either try moving the antenna around when you hear the inteference or use a magnet mount and move it around the vehicle to see it it goes away or gets better. If it changes with the antenna, then it is being induced from your antenna by something that turns on when your vehicle is started. What is your antenna setup? Roof mounted?
 

bullseye1584

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I took the radio to get serviced, they said there was a bad board, but i didnt ask which one. It was replaced and now works great. thanks to all that replied and helped!
 

K8TEK

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I took the radio to get serviced, they said there was a bad board, but i didnt ask which one. It was replaced and now works great. thanks to all that replied and helped!
You probably paid more for the board than what the radio was worth.
 

GSPD

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I've been running a couple GM300's for years and have experienced a similar problem as they aged. I have sometimes been able to just turn them off and then on and they'll work fine for a while. Now one is pretty much done.

It seems the circuit board connector pins are the culpritt in my case. That is the large multi-pin connector that terminates both top and bottom main boards. There is a reference to this on Batlabs about this issue and how to check numbers on your radio.

Again, this may not be your cause, but will create a similar problem.
 

cmdrwill

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It seems the circuit board connector pins are the culpritt in my case. That is the large multi-pin connector that terminates both top and bottom main boards. There is a reference to this on Batlabs about this issue and how to check numbers on your radio.
Very definite, the pins in the connector assembly are in a feed thru capacitor and these little feed thru caps break away from the pins and the ground/mounting plate. Also the plating on the pins gets in bad contact and Pro Gold applied with a Q tip works well.

Problems are :
radio does not stay on frequency and seems to drift.
modulation distorted
receiver microphonic ( also caused by bad VCO coil)
distorted receive audio
 

bullseye1584

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The board was free. It came off a parts only radio, that was laying around. Service guy was nice enough to do it for free. Thank you everyone for your comments. Much appreciated!
 

SCPD

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Free fix

I'm glad you got a free fix. I agree with the posters that said paying for a replacement board would of been more than the radio is worth.

It seems to me the first thing to do with a GM300, or one of the Radius mobiles like it, is to take it apart and clean everything you can get to. Blast everything with some canned air. Get any dust, junk, out of it. Unplug and re-plug every connector you can pull apart. Give the underside of the boards a good wiping with alcohol and a q-tip. Then put it back together. Seems to be always be the fix for any intermittent issues with these radios.
 
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