This may have already been covered elsewhere...but here goes...
I just received a HP-17BII with manual and the manual included a Manual Update sheet that listed two conditions that might cause a reset or memory loss. The Update is Titled: Update Number 1 and is dated June 1990.
Condition One:
1. RPN mode is active.
2. Start with a negative number in the display.
3. Leave the SOLVE menu or an ALPHA menu.
4. Type in another number. Notice the unusual display.
5. If you now use <backspace> to erase the display,
reset or memory loss may occur.
Condition Two:
1. Start with a positive number in the X-register and
a negative number in the Y-register.
2. Press X<>Y; a negative number is now in the display.
3. Type in another number. Notice the unusual display.
4. If you now use <backspace> to erase the display,
reset or memory loss may occur.To avoid Reset or Memory Loss - Press <Clear> to erase
the incorrect display.
An example on my 1987 HP-17BII:
Condition One:
1. Press 5 key, then +/-, then solve, exit,
display still shows -5.00.
2. Now I press number key, say 4, and display
shows .,004 with blinking cursor after the 4.
3. On this calculator, (so far), using backspace
does not clear the memory. But then the data
sheet only says "may", so maybe it only does
it randomly.
If you want to test this, be careful if you have a lot of stuff loaded into your 17Bii - otherwise it may all disappear.
Bill