> From: minimelisma
>
> That's exactly right. Before, nearly all of the buttons on
> the right panel worked, but you could tell that some of them
> were worn out because of poor responsiveness. Absolutely none
> of the buttons on the left were working before the
> replacement, so I chalked it up to a broken connection in the
> plastic ribbon cable. Indeed, upon removal of the panels, the
> plastic tails did crumble, so I confidently and carefully
> installed the new panels knowing that they would resolve my
> issues. Unfortunately, I'm right back where I started, albeit
> with brilliant new membranes. All of the buttons on the right
> side work and none of the buttons on the left side work, just
> as before. It's puzzling. I have LED illumination and control
> via linear potentiometers on both panels, however, so I've
> ruled out installation error. Must be component failure on
> the PCB pertaining strictly to the buttons, I figure.

I don't see anything in the circuit that only pertains to the left membrane
switch panel, besides the connectors themselves. Make sure the ink lines on
the membrane switch tails line up with the contacts. Sometimes the tails can
be cut off-center a little, causing a misalignment which can be fixed by
trimming the edge of the tail a little. Also, double-check that there are no
remnants of the old tails clogging up the connectors. The only other thing I
can imagine is that three of the outputs of Z1 are bad, but that's really
unlikely, since it's a TTL part, and they're almost indestructible.

If you still can't find anything, it'll take some electronic diagnosis, like
seeing if you can measure continuity between certain J8A and J8B pins when
certain switches are pressed (which will probably take three hands). The
service manual lists the connector pins corresponding to each switch, on the
last two pages.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...