HP 32E advice

[Michael Eckstein]

Hi, I have an HP 32E calculator with corrosion on the motherboard, see picture of the motherboard. After self test STO ENTER, the display shows -9,8,8,8,8,8,8,8,8,8, which is good, except for MSB number 9 instead of 8. Likewise, the numbers 5 and 6 are indistinguishable at that location. I have a question for an expert who would know the circuitry of the motherboard. From the picture, can you see the incriminated location on the PCB that controls the corresponding segment, or is one segment of the seven segment display unfortunately burnt out?
Thanks for your answers in advance,
Regards, Michael

[teenix]

The display board in the image looks pretty normal for its age.

Because the display is multiplexed, it is most likely that digit 1 has problems with some LED segments.

It is possible the problem lies in the IC's on the CPU board, but I'd still guess the display.

If you have some basic electronics experience, you can test the segments, by using a 3-5V supply and a 1K resistor and some test leads or wire. The test will require opening the calculator and removing the display module.

With the display removed from the calculator, looking down at the top lens with the pins on the bottom, pin 1 is on the left. Pin 16 is the cathode pin for the digit 1. Connect this to -ve on the power supply.

Connect the 1K resistor in series with the +ve supply.

Touching the unconnected end of the resistor on the following pins should light the corresponding LED segments.

3 Decimal Point
4 seg C
5 Comma
6 seg E
17 seg D
18 seg G
19 seg F
20 seg A
21 seg B

If any of the segments do not light, it is probably not repairable.

cheers

Tony

[Michael Eckstein]

Hi Tony,
I tested the display according to your suggestion and the E segment was indeed burnt out.
Thank you for your advice,
Regards,
Michael

[Michael Eckstein]

Hi,
I have one more question for an expert who would know the basic calculator wiring and IC circuit layout. Unfortunately when I opened the calculator the ICs fell out :-( and I'm not sure if they are inserted correctly now. I would hate to burn the IC's, I am attaching pictures of their relative placement. Please let me know if this is correct, thank you in advance.

Thanks for your answers in advance,
Regards, Michael

[AndiGer]

Michael,

IMHO the arrangement in your pictures is ok.

On E models the position of the 3 small chips doesn't matter as long as their orientation is right.

See this old thread:
https://www.hpmuseum.org/cgi-sys/cgiwrap...read=24353

Andi

[Michael Eckstein]

(04-08-2024 04:27 PM)AndiGer Wrote:  Michael,

IMHO the arrangement in your pictures is ok.

On E models the position of the 3 small chips doesn't matter as long as their orientation is right.

See this old thread:
https://www.hpmuseum.org/cgi-sys/cgiwrap...read=24353

Andi

Thank you.
Thank you. And regarding the large integrated circuit 1820-2162-A, is the orientation okay? The letters AMI and the IC designation are reversed from the other three chips.

[AndiGer]

I only have a non working HP-37E open at the moment. It has an HP chip no AMI. But HP readable in the visible window. IIRC AMI is also readable in the window.

The AMI should have a mark for pin 1 as well I guess

As Tony Duell mentioned in the linked old thread:
"pin 1 (notched end) of the IC points towards the display (this applies to the 40 pin CPU chip also)"

[Michael Eckstein]

Hello Andy, thank you for your advice :-) Regards, Michael