HP-12531 C and D

[Tony Duell]

> If it helps any, there are usually two numbers (at least) on the HP PCBs, one
> in foil and one in ink, the foil number specifies the foil pattern, the ink
> number specifies the component population.

I've also seen HP PCBs with an official lable stuck over the etched part 
number to specifiy different compoenns fitted. A classic example of this 
would be the microcode board in an HP9100. This is the board with the 
core-on-a-rope ROM on it, it's the same PCB in a -A and a -B, but 
different ROM 'programming'. The etched number is for the 'A version, the 
board in every -B machine I've seen ahs a label stuck over it. Or a PCB 
used for a ROM modele, the srtuck-on label depending on which ROMs are 
soldered to the PCB.

Mind you, sometimes there are different PCBs that differ only in the 
etched part number (!). The ROM boards in a 9810 and 8820 (2 boards in 
the latter) are the same electically. They're the same connections to the 
edge fingers, they take the same type of chips (8 HP custom ROMs) and 
have the same tack layout. The only differece between the 3 boards is the 
etched part number, and etched numbers saying what ROMs go where and what 
chip select line drives them .

-tony