@Retro Bowl From what you’re describing, it doesn’t really sound like a bad EPROM on its own — the random panel lighting when IC3 is removed points more toward a power, reset, or bus issue. I’d start by carefully checking the 5V rail at the CPU/EPROM, the reset line on power-up, and continuity around the EPROM socket, as a missing or unstable reset or supply can stop the system from ever properly starting even though the relay clicks.
