I'm not an expert in Allen Bradley, but I know something about PLC's. My problem is that I have an Allen Bradley PLC SLC 500 5/01, this one was working with other machine, we got from a surplus, I installed it in a new machine that needs PLC and when I applied power to the CPU just one led goes on (power) the other one (CPU fault ) is flashing (battery led it's off), I read something in the user manual and says that the CPU it's cleared so it's like new. The problem is when I tried to communicate with the PLC with a PIC 1747 and RSLinx 2.1 (windows 95) simply does not recognize it (does not appear a PLC, just my PC in RSwho), I can work great with the same cable and the same software with other machine with SLC 500 5/02. Can be damaged the CPU?, How can I work this problem?

Sence this SLC was surplus then it may have a program in it. Have you tried to reset it ( clear its memory)? See pdf below.

Default channel setting for a cleared SLC5/01 is 19200 baud rate and Node Address of 1.
RSLinx must match the baud rate and have a different Node address. ( had to say it just in case)