No subject

crowbar version. If you have a crowbar protector, the fuse will
blow if the the voltage even momentarily goes much over 13.8V
(I don't recall the trip voltage): this could happen if the PS
is set too close to the limit, or if the voltage sense wire to
the plug to the SB-104A has an intermittent open connection, in
which case it would occasionally sense an undervoltage at the
SB-104A and then turn up the voltage until the SCR trips and
blows the fuse.

If you have the pre-crowbar version, then it could be an
intermittent short in the SB-104A or PS wiring; a bad component
is unlikely if the problem only repeats occasionally. I don't
know if lengthy overdriving will blow the fuse.

You need to isolate the problem to either the PS or SB-104A. Does
it work again if you put in a new fuse? Put in a small fuse (5A or
so), unplug from the SB-104A and put a jumper in the PS to make it
turn on, and set the output with an accurate meter to 13.8V or a
little less; then try flexing the wires and plug to the radio to
see if that makes the fuse blow. If it doesn't, remove the jumper,
plug into the SB-104A, open its case, turn on (rcv only) and try
wiggling various wires (especially near the power plug) and
circuit boards to see if the fuse will blow. Try again in low
power xmit to a dummy load.

And of course, it could be other components - intermittents are
the joy of radio work.

I have schematics and parts lists of both the original (pre-crowbar)
HP-1144 PS and the later modification with the crowbar, but none of
my paperwork says "A" version. Let me know if you want copies; it
would be just copying cost and postage

John Farrington  KE5ZB

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