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Radio has strange problem

Peter Buckles Fondi

New Member
Jun 29, 2021
10
4
3
86
My radio was working okay, then one day I turned it on and I heard a loud squeal from the speaker. I looked at the meter and the needle was pegged to the right. Also, my transmit light was reddish blue. I'm using a Galaxy DX 959B with a 3 ft. roof mount antenna (Wilson Wini). I dove a half block and I turned on the radio and it was working fine. This happens intermittently. Some times there is no squeal. Just dead silence with the needle pegged to the right.
I'm not keying the Mic and it happens in different locations.
 

I'm not keying the Mic and it happens in different locations.

To me, I'd pull the MIC right out of the plug and see if the condition clears. Might just have a bad wire in the Mic.

IF it doesn't then it's internal to the radio - then that may be a different and bigger problem - a wiring mishap or the IC a 4558 (8-pin flat package) IC is having troubles - check side and rear panels for heating (2 Regulators) AM Regulator keying up, Shorting problem with the Finals (overly Biased MOSFET's are prone to keyups because of latching issues with the Gate) or the 8 Volts MAIN power Regulator is failing - feeling the panels and if they are hot it is being caused by an internal shorting / latching issue.
 
If this is a side-mike radio, sounds as if the mike socket has come loose and spun around. If it shorts to nearby D71, this can overload it and cause it to become an internal short circuit.

D71 serves to hold Q33 turned off in receive mode. When D71 shorts, the radio tries to transmit and receive at the same time. Seeing both red and blue from the front-panel status LED suggests this.

D71 is an issue in itself. It has two diodes or three inside it, wired in a series string. This way it will drop between 1 and 2 Volts when it is forward biased and conducting. Just pinning down the exact specs for what the schematic says is a type "KB362" was a pain. I suspect an undocumented production change. I really don't think the type number on the schematic diagram is the same as the part they used in production. And the part is just too tiny to have any printed ID on it.

Long story short, we use a series string of three 1N4148 diodes lap-soldered end-to-end to replace a failed D71. This produces enough of a voltage drop to keep Q33 shut off until you key the mike.

Of course, this might turn out to be a front-mike radio. Don't see this fault much in that style.

73
 
Last edited:
Thank you for helping. The radio is only 3 weeks installed. I'll send it back for repairs.
The seller tuned it before shipping. Bought 2 radios from BOB's CB
 

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