HP-97 Charging circuit not working

[swperk]

Hi Bob,

Thanks for the info! The manual you pointed me to is the same one that I already have, so any potential documentation errors are still there.

I was not aware of the other revisions of the -97 boards. My A2 keyboard PCB has p/n 00097-60019, which is the same as is listed in the replaceable parts section of the manual, so I figure this manual must be the one that is applicable to my calculator.

One thing I noticed is that the R2 location on my A2 PCB has no resistor installed. The service manual says that this is either a 200K or a 330K resistor that is "selected." I guess HP "selected" not to install one in my calculator! :-)

Even without that R2 resistor, the calculator appears to work just fine, as long as I keep the battery pack charged up with an external charger.

Barring any replies that advise me to the contrary, I will simply replace the open 8.2 ohm resistor once my Digi-Key shipment arrives. The data sheet I have for the fusible resistor does not say what amperage will cause it to go open. Assuming that it will open if more than 2 watts are dissipated, that implies it will fail open at a current of 350 mA (P/R=I^2). Does that seem reasonable, or am I making some bad assumptions?

Regards,
Stan