[AMPS] Alpah 77DX rcve bypass problem

[Don Moman]

Lost the receive path somewhere in the Alpha 77DX just before the end of
the WPX test this past weekend.  The direct/aux slide switch has been
by-passed so that isn't the problem. Transmit works fine. receive had
always worked fine before.

What I've seen so far: Antenna is routed fine from a cold start and thru
the 3 minute warmup. The first time it keyed it after that, it took a 1/2
second or so to get rcve back, next slightly longer and then quickly
refusing to work after that. Thumping the case had no effect. If you shut
the amp off, the rcve will come back in a few (5 to 15) seconds maybe.

What to suspect? Well the vacuum relay is about the only thing in the
path. So measuring the pull down point (Q301) on the QSK board showed that
to operate fine (55 volts pulled low when keyed, then comes back up
quickly). I thought if something was leaking here it might keep the relay
switched in tx, but that doesn't seem to be the case.  Yet something is
keeping it energized as shutting the amp off lets the relay go back to
receive.

I haven't a spare vacuum relay to pop in, but that seems like the obvious
thing to do, but in the meantime, anyone have any other thoughts? Residual
magnetism holding it on or??

73 Don




VE6JY  Don Moman               email: ve6jy@freenet.edmonton.ab.ca 
Box 127 Lamont, Alberta        email forwarding: ve6jy@rac.ca
CANADA  T0B 2R0  
(780) 895-2925       


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