7904A Basket Cases

Nathan Johnson
 

So I'm sure I was bidding against some of you, but I recently won two
7904As on
the auction site we all love to hate. They arrived at my house a few days
ago,
however I am not there, overseas again for my employer. I managed to get
the YL
to attempt to power them up, and they are in exactly the condition stated
in the
listing, one is completely dead with an appetite for line fuses, surely a
power
supply issue there. The other is more interesting, powering up with a
display,
collapsed and unfocused like the beam finder was stuck on. Messing with the
beam
finder button has no effect. Obviously the beam finder switch could be
stuck or
shorted internally, or components associated with it could have failed, but
what
concerns me is the possibility of a failed HV multiplier. I read somewhere
that
symptoms somewhat like this could be a result of the multiplier failing.
I'm
looking at the schematic and theory of operation and it's not quite
"clicking"
in my brain. Does the fact that the beam finder switch does nothing narrow
it to
issues in that neighborhood, or am I possibly going to need lessons in
multiplier construction?
Nathan KK4REY

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