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FADAL 1040-2A INTERFACE CIRCUIT BOARD DEVICES

All that TTL. We're gonna party like it's 1979!

After seeing this parts list, I'm gonna re-suggest checking the power
supply to this board, probably +5 V DC. If it's at all low or high, you
might look into why that is. (TTL parts draw relatively a lot of
current from the +5 V supply. Some of yours draw less - the 74LSxx and
74ALSxx part numbers - but in general, TTL boards require stout power
supplies.)

Here are some comments on what these chips are *probably* doing. This
may or may not help your problem, though...

U8- LM393P DUAL DIFFERENTIAL COMPARATOR

This probably works with CR to measure some kind of analog signal,
probably produced by a sensor with a variable resistance.

U13- NATIONAL - DM74ALS244AN Octal 3-STATE Bus Driver
U14- NATIONAL - DM74ALS244AN Octal 3-STATE Bus Driver
U26- NATIONAL - DM74ALS244AN Octal 3-STATE Bus Driver
U27- NATIONAL - DM74ALS244AN Octal 3-STATE Bus Driver

These guys might be in charge of talking to the rest of the controls
(the motherboard, other cards, etc).

U21-AMD 26LS33PC QUAD DIFFERENTIAL LINE RECIEVER
U22-AMD 26LS33PC QUAD DIFFERENTIAL LINE RECIEVER

These guys are probably in charge of receiving commands from the main
CPU.

CR- ICL8069DCSQ - LOW VOLTAGE REFERENCE

This should have an output of 1.20 to 1.25 V at 25 C (77 F). If it's
way off from this, you could have trouble. It probably lives pretty
close to U8.

C1- SQUARE FILM TYPE 103K
C2- DIPPED ELECTROLYTIC TYPE 10 uF

The "square film" caps are probably OK. The "dipped electrolytic" are
probably tantalums - they look like a little epoxy blob, often blue or
gold (but can be anything) on the end of two wires. I don't know much
about if these go bad or not; I will defer to others on this one.

CAP BRIDGING U21- SQUARE FILM TYPE 102K

Sometimes this is done because they forgot to design that cap into the
original board. Sometimes it is done to solve a problem that didn't
appear until later. You might make sure that U21 has a cap "tacked on"
to it somewhere - it can be on top of the chip, or on the bottom side
of the circuit board under where the chip is.

Matt Roberds