ML1400 FET Outputs - Damaged, or Not?

1766-L32BXB. I screwed up and forgot to wire the COM2 terminal to DC-

I cycled one of the outputs on and off a few times, and it was working, but then the output stayed on. The other outputs in the FET group also turned on when this occurred.

I immediately realized that I forgot to wire the COM terminal. I powered down and wired it properly. Everything is working fine now, but I'm wondering if I caused any damage.

The only things I had connected to the FET outputs were three 7W contactor coils, with suppressors (varistors), on outputs 5, 6, and 7.

I just found it odd that it actually turned on and off properly a few times without the COM2 connected



-Eric

I'm confident there is no damage.

Thanks for the vote of confidence, Keith

I would think the floating common should have no ill effects. I'm only concerned because it DID work a few times before staying high, which I thought was strange.



-Eric

The output circuitry of one channel can effectively use the common line 'felt' through another output. I've often had to trace these problems in a newly wired machine. The clue to a bad common is voltages on pins which are parts (1/3 or 1/2) of the applied voltage. There is usually a common missing somewhere.

Thanks, Bernie. That makes sense. The contactor coils connected to two other outputs would give it that path to DC common. Since I realized my mistake immediately, I didn't bother checking voltages.



-Eric