I'm working on a Grand Lizard system 11 pin. I was getting a lot of loud hum from the speakers at all times. I replaced both C2 (470uf 16v) and C3 (100uf 35v) on the MPU board as both had really high ESR as measured with my ESR meter. I also installed a couple screws that were missing for securing the MPU board to the back plate. That fixed the loud hum in the speakers that was present all the time. Now I just get feedback/hum when the CPU lights are activated.
I'm seeing a lot of AC ripple across the 30,000uf 25v filter cap for the lamp matrix so it looks like it needs to be replaced. I've got a new Big Blue that is used on the Atari power supply bricks. It's a 27,000uf 25v capacitor. Is that close enough to work?