On Mar 27, 2025, at 1:18?PM, Jim Bennett / K7TXA via groups.io <w6jhb@...> wrote:

Took a deep breath and removed C504. It measures about 500 uf so this cap is fine. No problem re-installing it. Other than my shaky hands!

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I did find an interesting thing while doing the testing. I had been using an Astron VS-35M p.s. in the shack into a boost-buck device set to exactly 12 v. It also shows current but I've found that to be completely bogus. Today I took the QMX+ to the garage workbench and connected it to my benchtop p.s. which is a lot more accurate than the boost-buck and is capable of current and voltage limiting. With it set at 12.0 v I did a key down on the QMX+. The output voltage stayed at 12.0 or so, but the constant current light and constant voltage light both flickered - and at the exact tempo as that machine gun sound on my headphones. Strange. I unhooked the radio and replaced it with another QMX+ that I built last year that works perfectly. No machine gun audio on key down and no flashing lights on that bench p.s.

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At this point I may have reached the upper limit of my debugging ability. Perhaps the only other thing I could try would be to remove D502 and test it, although it is a lot smaller than that tantalum cap and might prove tricky for me to attack.

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If you guys think it's worth testing that thing I'll give it a try. Or if there is something else that is within my capabilities... Otherwise it might be headed to Jeff for a New England vacation.

--

Jim / K7TXA
Eagle, ID

SKCC 10447T
BUG 301