On some sites external alarm input sensore does not work. It's everytime stay in same state - "open". If change AUX board we will have same situation - same alarm input sensores port does not work. This problem is exist on several stations but different ports.
Some sensores produce normal alarm, but several of them does not produce any alarm if we open or close external alarm input terminals.
We are check all configuration - it's ok. Check version consistency - no any problem. Check cable connection to OSN 3500 and found no any problem, all cables is ok. Then restarted (warm and cold) AUX board - no change. Changed AUX board and have same results, same ports does not work. This situation is repeated on other sites, only different port is not work.
Then we are change spare SCC board and switch to this board - problem was solved. We switch to main SCC board and problem is repeated again. We are change both SCC board and problem was totally solved.
We made change of SCC on all site and solve problem on all of them.
Possible reasons of problem:
1. Mistake in configuration
2. Version matching problem
3. Cable connection problem
4. Measurement problem
5. Because external alarm is connected to AUX board, so may be AUX is freeze or damaged.
6. SCC board problem - freeze or damaged.