Mike,
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I can feel your frustration from here. I experienced the same when trying to fix my TR4310 which had many, many wounds. There were several times it nearly bet me, but I beat it!
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The TR4310 and TR7 are not transceivers that I enjoy the mechanical layout of. It's never good when, in addition to having one, or more, faults to fix, it's difficult to get to parts of the circuitry you need to put a test probe on, or make some temporary modification to to prove / disprove a hypothesis.
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As Jim said, the 10 Volt RX / TX switching transistors are fuses, so get a few in stock. Would have been nice if the Drake designer had included current limiting / protection of these rails, of course, but no.
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Don't get distracted changing components randomly. Always try to follow the logic of a fault. If you need to, pull all the boards out, make DC resistance checks on the parent board and the boards themselves and build the radio back up - board-by-board - testing for DC and expected signals as you go. I stopped short of building a bench fixture that I could use to test individual boards outside of the radio chassis, but would not rule out doing so in future. It wouldn't need much. Just something with 5, 10, 13 Volt power supply rails would be enough to trace the DC paths on most cards.
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Keep at it!
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Regards,
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Mark, G4FPH.
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