HP -225 Owner's Manual page 157

3. Starting at the upper left corner ([Jz]) and moving from left to
right, press each key in the top row. Then, moving left to right,
press each key in the second row, third row, etc., until you've
pressed each key.
B If you press the keys in the proper order, and they are func-
tioning properly, the calculator displays KBD followed by two-
digit numbers. (The calculator is counting the keys using
hexadecimal base.)
B If you press a key out of order, or if a key isn't functioning
properly, the next keystroke displays a fail message (see step
4).
4. The self-test produces one of these two results:
B The calculator displays 225 - 0K if it passed the self-test.
Go to step 5.
B The calculator displays 225 - FAIL followed by a one-digit
number, if it failed the self-test. If you received the message
because you pressed a key out of order, you should reset the
calculator (hold down and press [LN]) and do the self-test
again. If you pressed the keys in order, but got this message,
repeat the self-test to verify the results. If the calculator fails
again, it requires service (see page 151). Include a copy of the
fail message with the calculator when you ship it for service.
5. To exit the self-test, reset the calculator (hold down and press
(LN]).
A: Assistance, Batteries, Memory, and Service 149