Another HP-67 repair query

[teenix]

(10-14-2020 11:24 AM)coitboy2000 Wrote:  Thanks Tony

With just 4V supply should I be seeing -12V somewhere on the cpu board ? The highest voltage I see is -11.33V on pin 2 of 1820-1596 and 6.3V on the majority of pins on 1820-1751 ?

1820-1751 = CRC chip
pin 28 is GND
pin 15 is Vgg = -12V
pin 2 is Vss = +6.25V

The circuit diagram that I have has the 1820-2530 ACT chip which I believe the 1820-1596 replaced. If they are the same then -11.33V would seem ok for pin 2, and about +6.25V for pin 1. Pin 12 is GND.

cheers

Tony