67 is flakey

[mbielman]

Let's look at this from a functional point of view. Maybe someone with knowledge of the ROM code
could help.

Power on and display shows 0. with exponent 00 (as if you pressed SCI 0).
Press a number key (5) and the display shows -5.000000000 00
Press ENTER and it displays 5. with exponent 00

ALL functions appear to work. That is, math functions like +, -, x, SQR etc.
Roll works, STO and RCL work, PI, things like that. Display modes (DSP, FIX, etc) do NOT work. (illegal operations like divide by zero show "Error" as it should.)

Cannot enter anything in PGM mode. Just displays 000

So maybe there's a ROM which handles display functions or does this point to the ACT?

FYI - all power supplies are spot on and no ripple, clocks and other signals look good, and tried a new PWO cap (no change). Card reader "tries" to work but I need to replace the roller (o-rings).

Also, ROM0 and ROM3 are AMI; the others are Mostek. The ACT is also AMI. (if that matters)