It's in an old (mid-80's) industrial machine. The French mfr. is out of business. The circuit I'm trying to resurrect takes a digital measuring encoder as input and displays the measurement on 7-segment LED displays. Display went wonky for a few weeks, then went blank, entirely. DC voltages and ripple are all good. Tried reseating socketed components; no joy.
Lacking any documentation, I'm going to try some "shotgun" troubleshooting by replacing the major components on the board (they're socketed).
Large components include: D8085AHC D8155HC D8279C-2 uPB8212C All parts NEC mfr.
When replacing with components available today, what are my limitations? (For example, I know "H" means HMOS, and that is a "must".) What else should I be careful re. the letter digits of the p/n's when selecting parts with the same numerical digits of the p/n's?
I know that the 8279 is a programmable controller, so replacing that without having the source code to program it with, is out of the question.
Just trying to help a client keep this otherwise good machine in service and avoid "binning" it.