During Field Day this year, my K3 developed a problem. The PA sensed
a high temperature and shut down the PA, displaying HI TEMP whenever
I tried to increase the power out above 12W. When I displayed the
temp from the front panel, it read over 100C and was not stable. It
drifted up and down, at times even reading -100C. (Seems like a 7
bit counter with sign.) When the temp reading was below 84C, the PA
was restored and everything (except the temp reading) was
fine. Checking the calibration, the temp reading can be varied over
a 40 degree range, just not the correct range. I took the PA and
KPAIO board out and examined the connectors, there didn't appear to
be a problem. The temp sensor appears to be inboard on the PA, that
is, on the interior side of the board, not the one near the fans. If
there was any moisture ingress, I don't think that it would have
affected the temp sensor. The front panel temp sensor appears to
read a normal temp and the fans work properly. Does anyone have any
suggestions as to where to troubleshoot the problem? What is the
voltage on the temp sensor (transistor)?
Ed K1EP
K3 #66
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