Most likely one of the four BS170 PA transistors has failed.? Usual cause is high SWR causing voltage breakdown.? The high SWR can be from an Auto Tuner seeking a match or an open feedline.??
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Take the cover off the QDX, then remove the washer arrangement from the four BS170s.? Transmit into a dummy load and feel if one of the BS170s gets hotter than the others.? The good luck replacing it, easiest is to cut the bad transistors leads.
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I had to do a replacement a couple of times, once I had to replace the driver IC.
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Chris
