I recently encountered an issue with an assembly machine:

After sitting idle overnight (or sometimes just over lunch, upon pressing the start button the machine would perform the first step of the sequence, then hang on the second set until the watchdog timed out. After repeating this sequence -

  1. Clear fault (electronically)
  2. Press start button
  • eventually the machine would resume normal operation and run until it sat idle for an extended period of time and the issue reappeared.

As I was troubleshooting this, I realized I was leaning on an assumption that I have used many times even though I am not 100% sure that it’s true:

An intermittent problem is the result of a mechanical action.

In this case it led me to a faulty safety relay fairly quickly, but it made me wonder:

Do electronic issues exist that could cause thus behavior? Are they common?

  • \$\begingroup\$ Poor designs, ground faults , ESD and EMI can cause intermittent faults \$\endgroup\$ Jun 7, 2021 at 1:10
  • \$\begingroup\$ Software errors, aged batteries, aged electrolytic caps, a circuit cooled by usage movements gets hot when idling, conductive dust settling (don't laugh), … \$\endgroup\$
    – mmmm
    Jun 7, 2021 at 1:17
  • \$\begingroup\$ Yes they do. Happy now? \$\endgroup\$ Jun 7, 2021 at 12:52
  • \$\begingroup\$ @mmmm how about carbonised ants, electrocuted walking across the high voltage area? \$\endgroup\$ Jun 7, 2021 at 12:52


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