New member: HP11C hardware problem? CLOSED

[johnc_19]

Hi. Hoping for some help regarding my 'new' HP11C:

I've been getting back into calculators with my son who is now taking the scientific route in high school. I previously owned two HP11Cs that were both stolen, the last of which was approximately 20 years ago. I have a new 35s and 50g and really haven't spent much time with them. I've always wanted my trusty 11C back so I decided to buy one off eBay.

I bought a nice HP11C unit and it passes the self test and keyboard test. Nonetheless, during use, I have an issue where the functions of my plus ('+') and minus ('-') operations seem to be reversed.

Example:
>4
>Enter
>6
>+
>Displays result: -2

I tried to do a memory reset and the display flashes 'running' and doesn't stop.

Is anyone aware of this type of behavior? Can it be restored somehow or is it likely a hardware problem. If hardware, can the hardware be fixed?

Sorry - it's been a while so I have lost some familiarity with the device. I'm hoping there is a simple solution.

Thanks!
John