Constant loud squeal when I turn on my Cobra 2000GTL radio

[SmilinDoug]

ok what about if you plug in a pair of headphones??? and can record a short audio of what the noise sounds like

The only headphones I have are USB. LOL

 

[SmilinDoug]

ok what about if you plug in a pair of headphones??? and can record a short audio of what the noise sounds like

I found some headphones at my Dad's. Plugged them in and got the same squeal, but just not as loud as the speakers.

 

[1iwilly]

thanks, it seems it comes down to a missing or bad ground, and the other time I've seen that issue was when guys would convert the 5-pin jack on the radio itself to 4 pin

 

[brandon7861]

This problem can exist in mics other than turner, so give it a watch at the 4 minute mark.

 

[SmilinDoug]

thanks, it seems it comes down to a missing or bad ground, and the other time I've seen that issue was when guys would convert the 5-pin jack on the radio itself to 4 pin

I am confused. It's not the first time so I'm kind of used to it. I was checking grounds to the chassis and everything was .8 meg ohms and climbing. So I checked from pins 7 and 8 at IC6 to the ground side of C172, and it was .6 ohms. Aren't all these grounds supposed to be to the chassis? Maybe they aren't and that might be my problem. Should I make a jumper wire and connect pins 7 and 8 at IC6 to a chassis ground someplace? I figure that's the easiest place to connect a jumper. I'm really sorry for bothering you guys.

 

[NZ8N]

Board Ground is DC isolated from Chassis (Case) Ground, and has capacitors around the edge of the board to couple the grounds together for RF (which is an AC signal)., and to keep the radio from squealing.

 

[nomadradio]

Like he said. If you want to make a DC-voltage measurement you can't use the metal chassis. It is a ground for RF voltages only, not for DC. This design quirk allowed the radio to function in a truck with the positive side of the battery grounded to the vehicle chassis. Diesel trucks were made this way to reduce corrosion between the engine block and cylinder sleeves in diesel motors. But when radiators stopped being made of brass, they were no longer grounded to the chassis. A plastic-box radiator insulated from the chassis makes the positive-ground vehicle a thing of the past. No more risk of an accidental circuit through the coolant loop.

Just the same, to get a DC voltage measurement, the meter's negative clip can go to the negative pin of the DC power jack. You'll get a more-meaningful measurement that way.

73

 

[SmilinDoug]

All this time I had to help my Mom and Stepdad move to New Hampshire. Now that they're gone I can get back on the radio. I talked to a friend of my Dads and he and I met at my Dads shop. He told me it sounded like feedback, and he said to spray some contact cleaner in the volume control potentiometer, which I did. The squeal is still there but it's a cleaner clearer squeal. LOL So I then started checking grounds and the ones I checked read 380 ohms. Shouldn't they be closer to zero? I've only checked three so far because 380 ohms doesn't sound right for a ground. I'm sorry for bothering you guys and I do appreciate the help you guys are giving me.

 

[nomadradio]

Does this radio still have the original five-pin mike socket?

Or did someone "convert" it to a 4-pin socket?

73

 

[SmilinDoug]

Does this radio still have the original five-pin mike socket?

Or did someone "convert" it to a 4-pin socket?

73

It's still got the 5 pin socket.