Finally, after more than three weeks testing and looking for missing parts, we have solved the problem of this Chinese made door access system. We have tried asking for help from most of our resellers but they could not help much. So, I had to test them during every evenings when I can help it.
It was not a matter of not buying from them as they had the same model but the nature of their business was that they did mostly trading and technical support was something completely new to them. Not only that, their notes are well guarded trade secrets. So, we had to do a lot of trial and error on this. Because of our fear of destroying the circuit, we had to do this slowly. I mean, we can buy another one again but this was not the option because if we chose it, it means we're not capable of the job.
Anyway, this afternoon, after much probing with the multimeter and more tests with one of my technicians, we got it done. Not only that, we also solved the problem of using only one power supply! Woohoo!