Been working on a Gottlieb System 3 dot matrix(Strikes N Spares). Game originally did nothing, I replaced a few fuse holders and game now powers up. MPU and both dot matrix controllers have the LED on, but completely solid. I replaced the power supply with an arcade one and get a good 5 volts at the connector on the MPU. If I remove/turn off the +5 via power supply, displays will display garbage, with +5 at MPU, displays have nothing.

Any System 3 gurus in here? What else should I be looking at? Powering the MPU without anything connected and with just the +5 from the power supply, the LED is still solid red. Bad MPU?

Let me know what you think!!!