[TenTec] Omni VI - LPF Relays Buzzing - Problem Solved

Terry Berman terrysb at gmail.com
Thu Dec 17 11:00:21 EST 2020

A couple of years ago I bought an Omni VI+ which arrived with an odd
problem.  At startup (and intermittently at other times) the relays on the
LPF board would buzz and essentially the radio would be inoperable until it
stopped.  Generally, this was about 10-15mins.

I started my troubleshooting by looking at the "bus" lines that traverse
through a number of boards in the radio which are used for band switching.
Indeed, when I was able to reproduce the problem I saw noise on all of
these lines.  After some time the noise ceased and band switching worked as
it should.

After eliminating loose/dirty connectors as the problem the schematic led
me to two possible causes - the chip on the Logic Board that takes serial
commands from the microprocessor which subsequently raises one of the
switching lines high or a chip on the Xtal Osc. board that is a line
driver.  At that point it wasn't clear to me how to isolate the problem as
these boards are all interconnected on this bus.  So, I took the shotgun
approach and decided to replace each chip.

I started with the logic board and replaced the IC there. No joy.

The UDN2985A on the Xtal Osc board was my next target.  I replaced it and
also the bypass cap.  That did the trick.  Buzzing gone.

Terry, KI3C

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