These are very simple computers. You could probably diagnose the problem with a multimeter and a logic probe (or oscilloscope). You'd check the supply voltages,

These are very simple computers. You could probably diagnose the problem with a multimeter and a logic probe (or oscilloscope). You'd check the supply voltages, then check the clock on the CPU, check the reset pin etc. But very often the problem is a capacitor that has gone bad, e.g. on the power supply. Have a look at arcade game repair guides. This one seems decent: https://forums.arcade-museum.com/threads/how-to-fix-pcbs-a-beginners-guide.177192/ https://forums.arcade-museum.com/threads/how-to-fix-pcbs-a-b... Make sure socketed ICs are properly seated. Good luck!