"electroninja" wrote in message
oups.com...
| Circuit board seems to have two varicaps or varistors on the largest
| power board (604101). Found one supply house that sells only one
| component for this board--a varistor. Seems odd.

That may be because they have those in stock anyway.

| In 1986, when this
| unit was made, does anyone know what designers used for timing
| control--no 555 chips to be found.

The CPU does the timing.

| Any posibility of a tunnel diode
| oscillator circuit for timing or temp control.

None at all.

| The zener diode in
| question appears (thanks Franc Zabkar) to be a 2 volt diode running in
| the circuit at 2.23-2.24 volts. If it were intended to bias a tunnel
| diode oscillator circuit, the extra .24 volts might mess everthing up.
| Any ideas?

I'm afraid at this point remote diagnosis seems unlikely to help further.

N