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Comparator with Hysteresis problem
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StillTrying:
I can't see any reason why that shouldn't work. LM358 outputs don't sink below 1V very well but with those high resistances it should be fine. Are you sure the LM393's R19 and R20 are really 100k and 5M1.
ranthalion:
They are pretty close to those values (1 percent).  I'll be able to hook it up to a scope tomorrow to see if that gives any new clues.
David Hess:
Comparators do not like high input impedances so it may be oscillating.
duak:
Are the decoupling caps on +12V right near U1 & U2?

Can you see anything unusual on U2A-1 with a scope when a triangle wave input signal is applied to the input? 

Since U2A isn't switching correctly, I'm thinking there's some spurious coupling to its '-' input.  A quick fix is to try 10 to 100n in parallel with R23 and if no joy then a few pF in parallel with R20 and then R19.
 
David makes a good point about possible oscillation due to high impedances.   I'd consider reducing the values of R19, R20, R22 & R23 by a common factor of 5 to 25.  Many spurious coupling paths are layout dependant so in the worst case, all of the changes may be needed. 
njmicheli:

--- Quote from: ranthalion on August 04, 2019, 03:17:21 pm --- So, it works if I am measuring the voltage, but not under normal operation? 



--- End quote ---

Is your meter probe completing a connection that is otherwise poor?
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