Erroneous HP-16C

[damaltor]

Hi everybody,

I have in front of me an HP-16c, which behaves oddly.

The good:
First of all, both self tests run without errors. But while using the device, the following happens:
- I calculated 15 minutes of random integers. No problems. HEX/DEC/BIN/OCT work like a charm.
- I noticed that converting to DEC takes a while (>3 seconds), while BIN/DEC/OCT are shown almost instantly. Is that normal?
- Floating point calculation works. I calculated 10 minutes of random numbers and tried most functions.

The bad:
- I cannot change the word size in integer mode. If I type "8 WSIZE" the calculator display blanks and stays blank. If I pull out a battery, and wait a while, and put it back in, random things happen - blinking display, or wrong calculations (3+3=2.5) or such. I can bring it back to function with a memory clear (ON+MINUS).
- If I go into PRGM mode and clear the programs, the calculator correctly shows "000-". If I start to type in programs, it always starts at line 85, and if I continue to program, the line number wraps around after line 91:

Code:

Key     Display
P/R     000-
1       085-    1
2       086-    2
3       087-    3
4       088-    4
5       089-    5
6       090-    6
7       091-    7
8       085-    8

The interesting thing is, the program works anyway: if I now press R/S, the display shows "12345 d" which is correct as the word size is 16.

Also, some key codes are shown wrong:

Code:

Key     Display
x<>I    085-000 72 (Should be: 001- 42 22)
x<>y    086-000 34 (Should be: 001-    34)
CLX     087- 43 35 (display is correct)

Most keys including the gold f-shift are wrong as far as I can tell (though the program seems to work fine as far as I tested, but I guess that would not work for longer programs).

Any ideas? My guess: The RAM is broken or desoldered, as the self test runs fine I guess that the ROM should be ok (though I dont know what exactly is tested in the self test).