Hi all,
Will KD4FOV and I have been removing what hair we have left trying to
troubleshoot a XO/LO board problem for the VI+ under surgery. (See the
archives for more detail.) The difficulty has been traced now down to a
non-functioning post-bandpass amplifier (Q7/Q8/Q9; Q7 + Q8 are buffer amps,
Q9 is a MPS3866 that does the 20 dB heavy lifting). It was working
marginally before when we were determining whether the bandpass for 40/30
meters was attenuating things. But now the amplifier section after the
filters has stopped working completely, meaning the receiver is completely
deaf on ALL bands.
Sadly, we're getting to the "stumped" phase without a working board to
compare with. Pulling the 3 transistors and testing them shows that they
are working OK (the hFE for the '3866 = 141 under test; plenty fine). This
section of the board is within a shield can and is pretty much impossible
to probe around in even if you pull off the shield (which we did).
Components are ridiculously tight. The signals go through a couple
autotransformers for the in/out and it gets really hard to probe things
with a scope before amplification.
At this point, I could really really use a working XO/LO board to swap in
for comparison. But these seem to be rare or never show up on eBay from
"parts mules". Gary does not have one (mentioned in an earlier thread).
Does anyone else have one? Anyone? Hopefully someone will chime in;
otherwise, I have a bad feeling about this project.
73
Phil W1PJE
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