Some systems just can't be fixed using normal repair methods.
We had a customer who called and said their system was not working.
So I went out and saw they had installed a new door, and they just needed a magnet installed. I installed the magnet and checked the rest of the system. All OK.
Then thereafter, every weekday at exactly 1:00 PM, there was a false alarm. I went out and checked it again. Asked employees about their arming/disarming procedures, etc. They told me they did not return to the office until 1:30 PM from lunch, so they were not even there! And no one else was there either.
I used every trick in the book to find any trouble with the system. Swapped out everything electronic too....
Next day, alarm goes off at 1:00 PM!
I then decided to play "detective". The next day, I parked my truck outside their office at 12:50 PM and asked our monitoring center to radio me if (when) the alarm goes off.
At 1:00 PM, I saw someone go into the office next door. Then the monitoring center radioed me that the alarm just tripped!
So I asked the people at the office next door if I could examine their door, they said OK, fine (they were aware of false alarm problems next door). The door had a wired contact on it, yet the office did not have an alarm system!
So I asked if that door used to be part of the office next door. They said "Yes. We re-partitioned the two offices so we could have more space over here." Arggggg! (Thanks for telling me about these minor remodeling details folks!)
So the solution to that problem was to take the door [next door] off the system....