I've been trying to revive an HP97 and some of it is already operating. But the thing that I'm concerned with right now is the behaviour of the kb. The leftmost part of it operating ok, but the right part (the one with the number keys) is dead. Can anyone tell something about it ?
This might be a bad connection between the CPU board and keyboard inside.
Take off the back cover and check the gold coated contacts. Probably one or more of the contacts is not making good contact. You might have to spread the contacts apart a little bit.
Another possiblity is that the gold plated contact grid under the right side of the keyboard has shifted out of place. (There are two grids, one under the left half, one under the right.) This has happended to me several times, but only after I've opened up the keyboard to clean it. It shouldn't shift while in use, unless the calculator was dropped or something.
Thank you for suggestions. I'll check them later today.
There is no obvious 'separation' between the 2 halves of the keyboard in the _electrical_ diagram of the matrix, although (electrical) rows of 4 keys are often either all from the left side or all from the right side. Do you get all the display digits appearing correctly (use the COS key or someting to get a display will 10 digits). If the display is fine, then the keyboard must be being scanned correctly (the same chip -- 'cathode driver' -- handles both).
For much the same reason it can't be a bad connection between the CPU board and the keyboard -- that would take out an entire column, which would include keys from both parts of the keyboard).
My guess is a mechanical problem with the keyboard. Take it apart (after removing the keyboard/display from the top case, take out all the screws on the back and lift off the PCB. Then remove the
insulators and the contact sheets. Look for coffee spills (!) and check that the parts are assembled correctly. One insulator either side of the contact sheet, contact sheet with the convex surface towards the keys.
OK, I'll do try this, because I've been checking contacts between the kb assy and the logic pcb but cound't find any thing wrong. TKS