Sounds to me as if the socket pin or a trace is going open between the
chip and the key connector. I'd check the traces by jumpering with a
clip lead using minigator clips. If there's not a pull up resistor
external to the chip (I'm too lazy to go pick up my Corsair II manual to
look) it might be that the chip is loosing a connection internally.
Before I tossed it, I'd not try jumpering the pin directly to the paddle
dash contact wire, but also add a pull up resistor, say 5 or 10K from
that input to +5. Without that resistor check the pin voltage on the
chip as well as at the dash connection.
A chip can have a thermal crack just like a PC board that only opens
when the chip is hot, could be two cracks, sometimes opens the
connection to the external world, sometimes the internal pull up. I'd
apply a quarter drop of Deoxit to the suspect pin and work the chip up
and down in the socket, IF I found the pin voltage different from the
paddle voltage. I'd also check every solder connection in that circuit,
probably with a microscope, or more likely with a hot soldering iron and
some new Ersin solder.
If the chip pin shows +5 volts while its in the continuos dash mode, its
almost sure inside the chip. But you see it low outside the chip so I
think its pull up, whether inside or outside the chip. If there's an
open trace or solder connection between the pull up resistor connection
and the chip (which could be a socket pin) either of these failures
could happen. A CMOS chip with no pull up can wander up or down and stay
where it lands for a long time. With an input current of pico amps or
smaller, the charge on a 470 pf capacitor can hold a constant voltage
for hours. Look for that pull up or circuit opening outside the chip,
but it could be inside too. Try the external auxiliary pull up. It may
be a cobble but a long term cure. My best thought though is an open
between the existing external pull up and the chip that also disconnects
the paddle pin.
73, Jerry, K0CQ
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