Problems with an Xantia

I have a 1994 Peugeot Xantia 2.0 automatic gasoline engine, and it's only generating spark in two cylinders. I tested it with an oscilloscope, and one of the transistors (it's a DIS) in the ECU isn't sending a signal to the ignition coil. I tried to find a replacement but couldn't. Someone offered me a used ECU, which I bought, but after installing it, the immobilizer is preventing me from starting the engine. I want to know how I can find out the code for that ECU (the car has a numeric keypad), or how to deactivate the immobilizer. Any help would be greatly appreciated.