Jon Elson wrote:

Michael A. Terrell wrote:

?
? CMOS is sensitive to spikes on the power rails. It sounds like
? someone should make a replacement board with modern ICs. It wouldn't be
? that difficult, with a schematic of the original board.
?
?
Obviously, Lincoln has this figured out. If operating inside a welder
with 300+ Amps and the HF system going doesn't upset it or cause random
failures, they did their homework correctly.

I also use 4000-series CMOS in servo amps with 120+ V and 20 Amps, because
they can run off 12 V rails, therefore more immune to electrical noise.


They will run off CLEAN 12 volt rails. Get some noise or ripple on
the supply rails or in the ground circuit and they get flaky, or go into
lockup which can destroy the chips. The 4000 series was the worst of
the CMOS families for problems. The 74c, 74 HC and 74 HCT families are
much better. BTDT, spent a lot of time with a scope to track down
erratic operation in CMOS circuits. One turned out to be bad PEM studs
where the board was mounted to the chassis and a ground loop was
modulating the supposed ground.


--
You can't have a sense of humor, if you have no sense.