Roy, thank you. That fits, so far, with what people seem to describe as part of the cluster of issues around the BS170s. Honestly, even if the BS170s turn out not to be the problem, starting with them seems prudent. They appear to be an Achilles heel. They might have come to me with one already blown, or I might well have blown one myself mishandling power to the device either at input (I did experiment with an "ordinary" radio battery just to see how the protection behaved) or at the output (I have used the device with an autotuner, and that's come up as a possible killer of BS170s).
I have an infrared thermometer, still in its packaging :-D I bought it specifically for future diagnostics like this one. Probably not quite as good as an infrared camera for this, but possibly better than touch alone.
I assume I should remove the retaining washer, or is result something I should be able to easily read with the washer in place?
It may be a few days before I can experiment with it again, but absent other advice, I believe this will be my next investigation.
Thank you!
Michael WD0OM
On Sat, Sep 21, 2024, at 05:10, Roy - KI0ER wrote:
Hi Michael.?
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When I had a blown PA output transistor, my 12v QMX was drawing a little over 200mA on receive/idle mode. So yours is behaving a little differently at 125mA receive current draw.?
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In my case one of the 4 PA transistors had an internal short from gate to drain. With the display board removed and the QMX powered up, I could feel (and actually see, since I had an infrared camera) one of my 4 PA transistors was getting quite hot during receive, which should not occur.?
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You may need help from one of the more knowledgeable electronic gurus, like Ludwig, in diagnosing what's going on.?
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But, if you can detect one of your 4 PA transistors getting warm in receive mode, then it's probably gone bad and needs to be replaced.?
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This is more of a hit it with a hammer type of diagnosis. You may need more expert help than I can provide.?
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73
de Roy - KI0ER
Littleton, Colorado USA
