Desktop 97 Display Question

[James Linder]

I have a 97 that does not display negative signs for either the mantissa or the exponent but shows them when printing. I do not think any segments of the display are faulty. Can anyone tell me what components are responsible for telling the display to light up the negative signs? I assume the components that are responsible for this will need to be replaced. I will probably start with the two display driver chips unless anyone offers an alternative solution. Thanks

[teenix]

(04-01-2021 02:24 PM)James Linder Wrote:  I have a 97 that does not display negative signs for either the mantissa or the exponent but shows them when printing. I do not think any segments of the display are faulty. Can anyone tell me what components are responsible for telling the display to light up the negative signs? I assume the components that are responsible for this will need to be replaced. I will probably start with the two display driver chips unless anyone offers an alternative solution. Thanks

If all other digits work ok then it points to the cathode driver or the connections between it and the LED display module. It could also be a faulty LED module.

Both the Mantissa and Exponent negative signs in the 97 are controlled by a single digit output. Unless the circuit has changed, my 97 Service Manual shows this output marked as C3/C15 and pin #2 of the cathode driver.

I'm pretty sure the negative sign for the Mantissa corresponds to segment [E] and the negative sign for the Exponent corresponds to segment [G] from the anode driver.

The reason for this is because the mantissa and exponent sign digits only have the [G] LED segment provided on the display module. The other segments [A..F and H] are missing as they would never be used.


cheers

Tony

[James Linder]

Thanks a million for your help! I will try replacing the cathode driver chip after I first confirm that all pins of the current chip are securely soldered in place. I have a lot of spare parts that came with a lot of 10 desktop calculators I purchased from a gentleman in Florida earlier this year.