docscarwash,
In the embeddied logic electronic world there is such a thing as a need for "debouncing of the pulse". That is usually accomplished through both hardware &/or firmware. Since getting into embedded logic recently more than I really wanted to do ... there also could be a solution (maybe) had with either a pullup or a pull down resistor in the right spot ... since it sounds like you replaced all the pertinent interacting components with the known good swapping technique. The pullup or pull down has the effect of eliminating stray electrical noise issues. I wonder if someone on the forum has a pulse counter or a very fast response voltage tester that could show what kind of unsteadiness of voltage pulse is involved.
Some pulse detectors are just looking for when the voltage is seen at O vdc or wide open (no voltage) which is different than a 0 vdc ground path ... so it seems that a problem with the ground wiring ... maybe no or improper bonding of the all the grounds is causing an unexplained grounding loop that could be an issue.
I remember when I changed to dollar
coin acceptors on our 16 laundromat dryers over 5 or 6 years ago ... I had to try some different relays accepting the pulse to avoid bouncing that would often cause double counting. Lo & behold adding a simple low cost Radio Shack relay (for pass through) provided trouble free operation finally.
I hope this helps ... let us know what finally solves what appears to be an electrical noise, ground loop, &/or a firmware debounce issue. All of these can somewhat be distinct issues IMHO.
It would be nice for us on the forum if we had access to a really good electronic engineer who would be willing to help us strike the right balance ... including long term costs for the electronic portions of our business from time to time.
mike walsh
www.kingkoin.com