HP 48G - Manual (Page 110)

If you suspect that your calculator is malfunctioning:
1. Run the self-test;
a. Turn on the calculator.
b. Press and hold fON ).
c. Press and release the “E” inenukey.
d. Release (ON). The diagnostic self-test tests the internal ROM
and RAM, and generates various patterns in the display. The
test repeats continuously until you perform a system halt.
2. Halt the self-test (system halt):
a. Press and hold (ON ).
b. Press and release the “C” key (the kejf with C next to it).
c. Release
( O N
). The empt}'' stack display should appear.
If the self-test indicates an internal ROM or RAM failure (if I ROM OK
and I RAM OK are not displayed), the calculator requires service.
If the calculator passes the self-test, you may have made a mistake
operating the calculator. Reread appropriate sections of the
documentation and “Answers to Common Questions” in Appendix A
of the
H P 4 8 G S e n e s U s e r ’ s G u i d e .
9-4 If Things Go Wrong ...