That's right. I just looked up the ECO (Engineering Change Order)
that mentions this switch as being redundant. Starting with the new
paint scheme in 1981 (blue stripes instead of the gray accents), this
switch was eliminated altogether and all OB-SXs came with 56 programs.
On an older OB-SX, it's possible that it was upgraded to the 56
program version but the switch was never removed.

--- In oberheim@yahoogroups.com , "litemakr" <litemakr@...> wrote:
>
> I used to have an OB-SX. If you have the 56 patch version, the
switch
> has no effect. You select the patches using a combination of the
bank
> buttons: A, B, C, AB, AC, BC, ABC, plus the patch number button.
You
> end up with a total of 56 patches using all of the combinations. I
am
> guessing it is something similar with the other versions.
>
>
> --- In oberheim@yahoogroups.com , "Paul White" <pjwhite@> wrote:
> >
> > --- In oberheim@yahoogroups.com , "synthy55" <synthy55@> wrote:
> > >
> > >
> > > recently picked up an ob-sx, it has a switch on the back to
flip
> > > between banks of preset patches, but nothing happens when you
flip
> > the
> > > switch, maybe you have to press a button as well , i don't have
a
> > > manual, anyone know how to do it
> > >
> >
> > I'm not completely sure, but I think the bank select switch is
there
> > for an _optional_ EPROM containing more patches. If you look
inside
> > the OB-SX, you'll probably see an empty EPROM socket somewhere on
the
> > main circuit board.
> >
>