HP-9100 with interesting problems

[dramsey]

There's a 9100B up on TAS that looks to be in cosmetically very good condition. However, the description lists these functional deficiencies:

"Addition, subtraction, multiplication and division work.

In degrees mode sin ( x ) and arc sin ( x ) works from 58.0 to 147.0.

cos ( x ) and tan ( x ) tend to get the same values as sin ( x ).

arc cos ( x ) and arc tan ( x ) work to values larger than
147.0 and less than 58.0.

log ( x ) fails and ln ( x ) fails.

e to x works but gets negative values.

sqrt works.

The register functions work.

The program control functions seem to work."

I'm not personally interested in the unit, but does anyone have any idea what could cause these odd symptoms?