Update:? Success!? I replaced the power supply boards, and my QMX HB is working great. All diagnostics look good, and I updated to the latest firmware, which will hopefully prevent this from happening again.? I'm going to see if I can repair the original power supply boards next and have parts on order. I think the D109 protection diode probably faulted, but haven't given it a real test yet.
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73, Dan - W2DLC
Daniel Conklin