HP-25 Co-luminous segments

[teenix]

(04-08-2022 07:10 AM)Tom Flatterhand Wrote:  I can't find the ROM0 chip. So, I can't find a chip labeled 5061-0430.

Another observation: in the picture of me shining a flashlight from behind on the circuit board where the two chips can be seen. It seems that the 4th contact from the left of the contact strip with the keypad has a direct connection with the 11th contact of the contact strip to the LED display. This is very strange to me since it is this contact of the keypad that connects to the middle row of keys? What is this directly to the display?

Sorry, I was confused with the HP-27 problems. ROM0 in the 25 is part 1818-0168

You'll find many keyboard connections connected to the LED display. Both are multiplexed together to save pin counts on the ICs and keep the circuit boards simpler.

cheers

Tony