HP97 The journey begins

[Dreato]

I've done 4 HP97 refurbs. All required card reader rebuild (O rings and shaft coupler), Printer rebuild (new idler gear and O rings for paper advance). 3 of the 4 also required replacing some Tantalum capacitors. I usually think of these as extremely long lived, especially compared to normal electrolytics, but for these calculators this was not the case. Two of the tanatalums actually broke apart when I wiggled them. I made a charger transformer from a 10VAC wall wart and a custom plug. I also changed the current limiting resistor, since I used NiMH cells in the rebuilt battery pack, and I believe they're sensitive to overcharging. I changed R3 from 8.2 ohms to 47 ohms. This reduces the charging current to ~ 100 mA.

Regards,

Dave