In opposite, the dry contact specified for relay no.2 only picks up one of the two relays because of diode inverse biased activity. In this case diode blocks applied voltage to relay no.2 .
After some time the diode fails due to overheating and it must be replaced by a similar diode. But maintenance man can't find the diode with the same characteristics in market, and he decides to use an over size option. The replaced diode had the same rating of voltage but the current-carrying capability of it was more than the last diode.
It seems all things are okay. But sometimes the circuit can not operate correctly. For example in some condition the auxiliary relay no.1 doesn't drop out after one temporary close-open command.
Indeed when two dry contacts (C1, C2) run up related relay and only the contact C1 return to first position, the relay no.1 doesn't drop out and remains in holding position.
How can you explain the reason of this problem?