Todd Micaleff created a great site for Datron 1281 DMM repair and calibration.
https://xdevs.com/fix/d1281/This site allso collects a lot of detailed design information - as usual for the xdevs teams.
Several proud 1281 onwers (like me) are supporting by their findings - but the info belwo may also of interest for others.
Background:
I faced a fault on one of my 1281 - I could located the damaged on digital assembly - a 8 MHz oscillator IC not oscillating.
That fault had some negative impact also to other digital parts on the board - but that's a different story.
The digital assembly (CPU board, 68k based) used at the 1281 is used in several Datron gears like 1271, 1281 and 4920.
During lifetime it had several revisions - I own two 1281 with different CPU boards, both with same Firmware (v3.12).
- the older one is using 2 PALs and many TTL ICs to handle the different adressings (Memory, I/O...).
PAL1: Uxxx, 14L8 [No 290161-1, Date 25-MAY-88], I have no "old" doc to verify the part reference
PAL2: Uyyy, 14L8 [No 290162-1, Date 29-MAY-88], I have no "old" doc to verify the part reference
- the newer is using 3 PALs to reduce part count.
PAL1: U107, 14L8 [No 400902-10, Date 24-MAY-89]
PAL2: U111, 14L8 [No 400904-10, Date 24-MAY-89]
PAL3: U110, 20L8 [No 400903-10, Date 24-MAY-89]
I don't own a PAL/GAL Programmer which is able to read 14L8 or 20L8. that products.
Both, 14L8 and 20L8, are PALs without latching - so read out is no big deal.
So I reactivated my last century DIY PC-Printer I/O expander (my CtrlLPT - yes the SW is based on MS-DOS).
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/PeLuLe