HP-97 troubleshooting

[Paul Berger (Canada)]

(04-06-2020 10:34 AM)Kees Bouw Wrote:  Hi,

Some general questions about HP-97 troubleshooting.

My newly restored and cleaned HP-97 shows only the low battery light when switched on. The battery is not actually low, and besides the same thing happens when I connect the charger. What would you check?

Is it safe to operate the HP-97 with the printer unit and the card reader unit not connected or removed?

The card reader is located in a such a position that it is impossible to measure anything of fine-tune it. Is it possible to have the card reader unit connected from outside the calculator? Can it still work correctly if you connect it with a long flat cable (let's say about 20 cm)?

Thanks very much for any help!

Kees.

As Andi mentions the printer card must be in place as the LC tank for the clock is on the printer card. The low battery LED is turned on by the cathode driver chip so i would suspect it includes circuitry to check battery voltage. Battery voltage is connected directly to this chip, so I would suggest measuring the battery voltage at the cathode driver in case there is a bad connection somewhere. Are you measuring the battery voltage with it installed and the unit turned on? That would be the only way to reliably know if the batter voltage is sufficient or not since something inside may be pulling it down when you turn the unit on.

I suppose you could operate the card reader outside the unit but I am not sure why you would want to do that. I would avoid unplugging the cable to the card reader if possible, those cables are now all pretty old and are prone to falling apart. If you do unplug them you need to slip a piece of thin plastic in between the cable and the connector contacts before pulling out the cable otherwise the pins will dig into the cable and almost certainly wreck it. I use pieces of PET cut from plastic bubble packs.

Paul.