On Sun, 31 Jan 2010 12:16:53 -0500, j wrote:
>One of the Titan 425's at the contest club station will not standby.
>It has the standby/operate switch, when in operate, PTT works and the
>vacuum relay pulls with PTT. When in standby, there is something like a
>RF sense that keys amplifier and the relays can be heard when sending
>'dits', PTT does not pull in.
>Any thoughts? Thanks.
Perhaps the main antenna relay (a vacuum relay) is bad. The 425 includes
logic to detect whether or not the relay is pulled in, and also the
condition of the PTT and/or key line. There could also be a problem in that
logic circuitry. It's fairly easy to work on -- the vacuum relay is on a
small board right behind the input coax connector, the logic is on one or
two boards under the tubes that you get to by turning the RF deck upside
down removing an access panel. In both cases, you must take the boards out
to work on them. I've had to work on this circuitry several times, and my
Simpson 260 does a good job of finding bad transistors, diodes, and
resistors. All the parts are pretty standardard and inexpensive. No house
numbers, nothing you need to buy from Ten Tec at inflated prices. I've
always had everything I needed in my parts stock. Replacement vacuum relays
are available from GigaVac, with a special discount for hams. I don't know
a source for the smaller relays, so you may need to buy from Ten Tec if
they are bad. The most common problems, however, are the big relay and
various semiconductors.
The schematics in the Ten Tec manual spread this circuitry out over several
pages, and are a PITA to chase. I've redrawn them using Autocad, putting
everything on one sheet of paper, maintaining identification of what
circuitry is on which board. They are on my website as .pdf files.
http://audiosystemsgroup.com/publish.htm
73,
Jim K9YC
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