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Post by jaliv94 on Mar 24, 2022 15:27:16 GMT -5
Just fired up my Mark 4A For the first time in a couple of months. When I keyed the mic I got the typical squeal but the receiver did not completely disengage. I could hear my voice through the speaker. Relay? 776 mike? Ping cap?
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Post by 2600 on Mar 26, 2022 0:27:25 GMT -5
Relay, maybe. If the filter cap C320 that runs the relay and nothing else has failed, it can cause the relay to close only part way. A failing filter capacitor reduces the available current to the relay coil.
If that cap is original, just change it. If it doesn't fix this problem, at least it won't cause the next one.
And if it's already been replaced recently, the relay and/or the PLL lock-detect lockout transistor Q304 are next. You can take the lockout transistor Q304 out of the picture. Find the hot wire on the relay, usually the rearmost of the two coil lugs on the socket. Usually a yellow wire. Follow it to Q304's emitter. Take that end of the wire loose and solder it to the pad where the positive lead of C320 is soldered.
And if that won't make a difference, maybe you do need a relay.
73
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Post by jaliv94 on Mar 27, 2022 17:30:05 GMT -5
Thanks for the reply. Independently of that problem I reworded my 776 because the previous owner of the mic made a mess of things. New cord, better solder joints and cleaning of the switches with alcohol (everclear) seems to have solved the problem. Don’t know if the mic was the problem or just part of a problem that will rear it’s head at a later date.
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Post by 2600 on Apr 2, 2022 0:24:58 GMT -5
Way cool! Sure makes it sound as if maybe the mike wasn't letting the relay coil get full current to it.
Dontcha wish more problems turned out to be that simple?
73
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