HP portable / HP 110 Service Manual

[S0N1C]

I only now found time to disassemble my HP 110, it is not so easy because I wanted to preserve stickers (and I did) which hide majority of the screws. So, I opened it, pulled ROMs (yes, pulled, they're in in-board sockets!) to read and then decided to install them back and check, and lo and behold ROM test completes with OK and Lotus 1-2-3 works fine, so it was probably just a bad contact with socket.

But to be sure I dumped a working copy (I don't know what type of ROM this is, so I just used generic 27C256 settings) I tried burning it to my EEPROM chips, unfortunately I have only 27C512, so not an exact match, but I filled each chip with twice as much data and installed. And they work, Lotus runs, I didn't see a difference but when I ran internal ROM test it gave me errors on both chips maybe it reads IDs? Anyway, I call this success
On a side note, my HP 110 had a poor contrast display even on the highest setting, max LCDNEG I measured was -11.6V, not sure what was the actual reason, first it looked like STEP8 wasn't working, I checked MOSFETs(Q8-Q11) and they were all fine, then I began swapping resistors and now it looked like all steps are working, I tried many configurations(late at night, so no exact recollection ) but in the end I replaced original resistors with 200K, 100K, 47K and 22K and now on the highest contrast setting it goes just a little over -13V and display is dark but readable.