Sharp VCR Tracking Incompatibility
 

Hello:

I have a Sharp VCR (circa 1995, Model VC-A323U), which I would like to
use exclusively for time-shifting. It records and plays just fine
(using EP mode throughout this discussion). I have no schematic or
service documentation.

When I attempt to play a tape which was recorded on my other VCR
however, it struggles for a while attempting to auto-track. The result
is "almost" good, but there is some residual vertical "jumping".
Figuring it's probably at the limit of the auto-tracker, I have
discovered that I can tweak the mechanical A/C tracking slightly, and
dial-in a perfect picture. Unfortunately, when I eject and re-insert
the tape, it does the same thing (auto-tracks to a less-than-ideal
result, jumps vertically). Again, I can tweak the mechanical A/C
tracking and achieve a perfect picture. Try as I may, I am unable to
converge on a mechanical setting that works consistantly. I'm
convinced that this behavior is not erratic ie: the auto-tracking seems
to consistantly drive the tracking to the same (poor) spot with
residual vertical jumping. This never happens with a self-recorded
tape.

I'm not attempting to achieve a result that is "calibrated" against the
universal VHS specification. All I'm asking for is to be able to play
tapes previously recorded on my "main" VCR. I realize that the "main"
VCR could be at fault, but since it's a much newer unit, and I have a
history of borrowing / loaning / renting tapes without a problem (as
well as a library of archived tapes), I'm unwilling to mess with that
one too.

Questions:

Is there any way to defeat the auto-tracking, and just go with my
manual A/C tracking setpoint? I assume the "proper" way to adjust the
mechanical A/C tracking would involve somehow disabling the
auto-tracking so the mechanical position can be centered?

I have read Sam's FAQ, which has a section on tracking
incompatibility... One possibility mentioned is the roller guide
height. Everything seems tight, and I have not tried altering the
height yet. Given my symptom, does this seem like a likely
possibility?

Is there some kind of a "bias" in the auto-tracking loop that can be
adjusted? I can consistantly adjust the mechanical A/C tracking to
achieve a good picture, so perhaps the auto-tracker is simply not
seeking the proper sweet spot.

-Thanks
Tom