Excellent Terry
On Thu, Dec 17, 2020 at 11:00 AM Terry Berman <terrysb@gmail.com> wrote:
> 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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