Here is what happened. Pinball wouldn’t boot. The cpu was measuring 0.5v on the test point
We unplugged the power cable from the cpu and verified the system 11 power supply is producing 5v all the way to the power plug to the cpu.
So, we deduced the there was a short on the cpu.
I removed the cpu to bench test, using my professional grade, adjustable power supply. I set it to exactly 5v output. Using the test ROM in the board and hooked to my professional power supply, the game tests 100%. Zero issues.
My question was, is it normal to be reading 4.4v on the cpu test points while my poser supply is providing 5v? Seems low too me, like there is a short, but it is passing all tests perfectly. That’s why I wanted to ask.
As for the next question....why the voltage was going from 5v to 0.5v while in the game and using the sys 11 power supply that is in the pinball.
My belief is that the bridge rectifier is out. It’s producing the correct voltage at initial inspection, but it’s shorting out when the cpu load is on it.
I swapped bridge rectifiers and the 1000uf cap. Will see it that was it. I ruled out fuses, fuse clips, and headers. After this, the only thing left is the other caps and NPN on the heatsink