HP-45 one digit only

[teenix]

(01-04-2023 05:30 PM)geologie Wrote:  Hi, i have an HP-45 that only register one digit number. If i enter, for exemple, 20, the display only shows 2 and if i square the number i get 4. If i continue squaring, i get the good answer on the LED. The display is all ok, the keyboard is all ok. I resolder the main board connection without any change.

A friend that also have a 45 bring me his board and if i put it in my calculator everything is fine, so my main board is bad. Now that i have another good board with me, what can i check and compare to repair my board?

Thanks

The display anode driver gets its information through the 5 interconnect pins on the lower left of the calculator. These might need checking.

Check the 2 coil modules at the top of the PCB. These provide the energy for the LEDs.

Other faults may be the anode driver or cathode driver IC. Also, the A&R IC drives the anode driver, it could be faulty as well. In these cases, only an IC or CPU board replacement will fix the problem. Forum member, Harold, has (or maybe still has) replacement CPU boards for Classics like HP-45.

The rest of the CPU board seems to be functioning ok.

There are some notes on the Classic display operation in my Classic Notes PDF file.

A circuit for the HP-45 can be found here

cheers

Tony