Please help me find my preamps short circuit or blown component.

I need help with a preamp. My preamp is controlled by keypads plugged into an rj45 port.
The port has 8 wires

1,2,3 zone selection
4 rs485
5 rs 485-
6 12 v
7 ground
8 other

It is my understanding that the keypad control the amp through an optoisolator circuit.
Any way a keypad shorted out and then it shorted out the preamp. Not knowing I had a shorted keypad I then put another preamp on and it shorted and to make things worse I repeated my mistake.

Thus I shorted three elan z630 preamps. I know need to figure out how to fix. What is the most sensitive component? Is it the optoisolator? the resister etc. I have no circuit diagram.
I could provide pictures of circuit board and thats about it.

Which of your identical topics would you like to receive replies?

or the second

clever clever