HP-45 one digit only

[geologie]

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

[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

[geologie]

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

[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