I turned on my Apple IIe today. But the keyboard, which worked well two months ago, is not working a little today. It only enters the same character no matter what key I press.
Looks like a problem in the keyboard ROM chip. This 2716 EPROM contains the key mapping, that determines what key corresponds to what character.
The character you are getting is mapped to the DELETE key and its code happens to be 7F, which is 1111111 in binary. In other words you get it when all 7 output bits coming out of the keyboard ROM chip are high. You will also get exactly this result if you replace the keyboard ROM with a blank EPROM chip, since all its bits will be 1s.
The first thing to try is reseat it and check its socket. Then if you have another random non-empty 2716 EPROM chip put it in its place and check the result.
May be worth checking the encoder pins are getting energized the correct way... as an example when you press a key there should be a short between two between Encoders for example: pin 37 and pin 20(V), 21(B), 22(N), 23(M), 24(<), 25(>), 26(/). Only one short should be present for each press. If not there's something wrong with the keyboard. But the odds of this being your problem I'd say are pretty low. If any key press shorts pin 23 and 33 then that would explain why you're getting the delete key (that's the correct short signature for DEL). DEL is also one of the highest priority keys when scanning but that's likely not the problem.
If you have an EPROM programmer, could pull the chip and verify against known images. If those two check out it could be the encoder, but testing the keyboard encoder output is more difficult because you'd need a logic analyzer and a little bit of signal decoding magic.
Thank you. I forgot for a moment that I was fiddling with chip cuz I was bored. Reinstallation works.