HP-45 one digit only

[teenix]

(01-04-2023 09:48 PM)geologie Wrote:  Wow thanks for the documents. Here is what i've done :

I powered 2 HP-45 one with bad main board and one with good board. I powered them on with the same bench power supply. I read voltage here and there at power on state (0.00 on both screen). I notice a great difference only on these pins on U1:

KR1 to 8 and KC1 to 5. On the good board, KRx voltages are all 0.9V, the bad are all 6,1V. KCx on the good board are all 0.2V and on the bad one all -12V.

I also read a 6.1V on the gold square where the IC numbers are ! On the good board, no voltage on the top of the IC.

My two board are not identical. The bad one is all gold traces and date 73 and the good board is aluminium trace and date 74.

Can i do something on my bad board, the other one is not mine...

Thanks

6.1V is VCC and this connects to pin 1 of U1 C&T IC. You should see a gold strip running from pin 1 to the gold square, so VCC will appear on the gold square as well.

It is possible that U1 has failed. Is it (or any other ICs) warm to the touch when it has been on for 30 secs or so.

cheers

Tony