I am trying to repair an HP-67 that almost works. In PROG mode, everything works OK, I can enter a program and edit it. In RUN mode, things look strange. Programs appear to run OK, but the numbers on the display are all wrong: There are leading zeroes, and when you press numeric keys, they are displayed with lots of extra digits. Its not a DSP or format problem - this behavior is consistent from power on and is totally different from that of my HP-97.
The problem looks like it is localized in the RUN mode display, constants like Pi are recalled to the display, and (as far as I can tell from the weird displays) registers and numerical calculations work.
I suspect the problem is in one of the ROMs, but I can't tell which. I only have access to the HP-97 service manual but this is not much help, because the 97 has more chips.
I am including some notes I made while looking at the 67, if anybody can provide additional information, I'd really appreciate it.
**vp
8-pin chips (ROMS)
1818-0550 (also 0228) common with HP-97
1818-0551 (also 0226) common with HP-97 (this one contains constants like Pi)
1818-0231
1818-0232Card Reader Chip
1820-1751 (largest chip) common with HP-97Processor(??)
1820-2530 Mostek part???
1818-0268