Quoted from Indigestion:
First posting - not sure to the rules Of the forum but adding to this topic since it may be related.
I just pushed to 3 my pinball collection by buying a Tri-zone, a system 6 machine. It does not boot up. I have 2 LEDs on constant with play field on. No display lights although from an angle I can see there is power going to them.
When I first fired it up, I had some numbers going to the displays that eventually went away.
My question this: I have checked the voltages and I am only getting 9 Volts DC in the 12V unregulated supply, both on the MPU board and on the power board. The 5V is good. The F5 fuse and the C15 capacitor all have 9 V going to them.
Any ideas on what could be limiting the voltage from reaching the 12V dc?
12V unregulated is created by D7 and D8 on the power board. My guess is that one of these diodes has failed or you have a bad connection on the AC supply side into the power board.
When one of the rectifier diodes fails, you are missing half of the rectification of the AC to DC which drops the DC voltage. It also wreaks havoc on your filter capacitors so don't run the game like this for long.
The reset circuit on the CPU board needs to see 5V and 12v unregulated at certain levels before it lets the CPU start. It is possible your low 12V situation is the cause of the game not starting.