The CPU booting only sometimes might not be something to get too concerned about... the POWER FAILURE cct has a timer attached to it and needs the 5V on pin 8 CN11 to be on then removed then on again.... you are tricking the CPU to boot by doing this and sometimes it doesnt work... also sometimes it will boot without the pin8 removal..

The power board is what concerns us most right now... you should have around 43VAC coming in from the transformer.. test this across pins 7 and 8 CN1 ( pin 7 feeds fuse F5)... you should then have 39VDC at pin4 CN2, 5&6 CN3, TP5 and 3&4 CN4... if you dont have approx 39VDC then the bridge P5 is gone and needs replacing.. also replace R21 ( 680 Ohm 10W) at the same time.

While you have the board off replace the caps C6 & C6 ( 10,000uf 20Vea).. also C7 ( 0.33uf) D4 ( 1N4003) R12 ( 100 Ohm) and lastly C8 ( 0.1uf)... this is your smoothing cct and also feedback cct to 5V regulator... this will clean up the 5V and smooth any ripple out.

Now if we are lucky ( which we are invariably not with Zac games) the CPU should boot OK in the machine... if not and TP7 is still fluctuating ( this is cap C5 charging and discharging) then we have a fault with this cct either on CPU OR power board