The thing I forgot to mention is that the 253 uses an 8 pin DIL non-volatile
ram chip to store the settings. The same chip is used in the Omni-V and maybe
in the Omni-VI. That chip has a finite life and after a LOT of use, the tuner
(and the Omni-V) develop amnesia. Erratic band change operation is a symptom
of this. It simply fails to remember correctly the last setting.
I could not find any over here and the original X2404P chip may no longer be
available, but there is a drop-in CMOS version X24C04P. I have been told
these are widely used in gaming machines. They were pretty inexpensive, so I
got a dozen of them from Newark.
In my 253 the X2404P chip is socketed, but very awkward to get at - it is
behind the front panel. In my particular Omni-V it was soldered in, so when
the amnesia appeared and I found what causes it, I removed the chip and
replaced it with an 8 pin DIL socket, in case I ever needed to swap the thing
again.
Whether you need to know this probably depends on how much re-tuning and how
much band changing you do. With one mismatched antenna for all bands and
lots of re-tuning, the 253 chip gets to do more work ... Likewise in the
Omni, if you leap around a lot, storing different settings, the chip gets
more use.
P.S. when I took my Herc II on its 4000 mile trip to Sevierville, only one
transistor was down. But because TT could not match it, they swapped all
eight. It has been fine since, except for a vacuum relay (OUCH) and the
present intermittent fault on 10/12m.
John G3JAG
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