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What caused L39 to burn up ?
- Thread starter Brian G
- Start date
Well, the best I can remember L39 is the choke thru which the collector current for the final is fed. So if the Final shorted from collector to emitter it's plausible that could get the choke pretty warm but a proper fuse in the radio should have prevented that, "I think" but maybe not it is unusual to see that choke burned.
Final is most likely toast. The AM modulator transistor TR41 and the choke, of course.
When a final transistor breaks down inside, components on the input side of the circuit can become 'road kill' and have to be replaced as well. A bright light and a hairy eyeball on the parts alongside the final may reveal signs of overheating.
Definitely want to make sure the fuse is no larger than 4 Amp size.
This switch has enough circuits to replace the original mode selector. Pin layout may be different.
https://www.ebay.com/itm/144066275676?hash=item218b04e95c:g:w0YAAOxymiVQ~6ag
73
When a final transistor breaks down inside, components on the input side of the circuit can become 'road kill' and have to be replaced as well. A bright light and a hairy eyeball on the parts alongside the final may reveal signs of overheating.
Definitely want to make sure the fuse is no larger than 4 Amp size.
This switch has enough circuits to replace the original mode selector. Pin layout may be different.
https://www.ebay.com/itm/144066275676?hash=item218b04e95c:g:w0YAAOxymiVQ~6ag
73
sorry, it’s L42 not 39. So likely it’s the driver area then that has issue? And or is there something else I should look at?
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sorry, it’s L42 not 39. So likely it’s the driver area then that has issue? And or is there something else I should look at?
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L42. Driver transistor, not final stage.
An additional hazard when this happens. A shorted driver transistor may "sideswipe" D50. If it fails short, A new driver transistor won't work. Yet.
And if D50 fails open, the new driver transistor and the new L42 could get smoked first time the mike is keyed.
The bias-current test will tell you if the driver transistor's input circuit is okay.
73
An additional hazard when this happens. A shorted driver transistor may "sideswipe" D50. If it fails short, A new driver transistor won't work. Yet.
And if D50 fails open, the new driver transistor and the new L42 could get smoked first time the mike is keyed.
The bias-current test will tell you if the driver transistor's input circuit is okay.
73
How do i test this circuit without frying the choke, transistor, or mode switch? I know the bias check procedure but if there is a good chance I will fry components as soon as I key the mike, that makes it difficult...thanks
I believe if the two bias wires are unhooked from the board there will be no power going out. So no parts will be burnt.
Thank you . I will try to test the diode with my VOM. Assuming it is good, then what would be causing the burning up of the choke/driver? A bad solder joint/connection?
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D50 checked out ok. D49 however did not. I did previously have a burnt final so I think that has been toast for awhile. I will find a replacement for that.