When testing resistance/continuity/beep, the game would be off. Voltage measurements are always with the game on.

I seriously don't know how you can tell any of these boards will have bad solder not even knowing what board is at fault.

I have never seen any bad solder on any system 11 games in my 11 years, unless someone did a bad repair job.

So here we wait for your answer to Grumpy's post.

Once you establish 5v is at least 4.8v on the CPU board, please report what is the state of the blanking and diagnostic LEDs on the CPU board.

You still need to measure the 5v on the MPU. If it is good, sounds like there is a bad part on the board. What all work was done to the MPU? Just wondering to see if it can be potentially related the error codes you are currently seeing.

Just the 5v on the MPU as Grumpy mentioned. If is above 4.8v, better consider sending it to ChrisHibler for repair. MPU bootup issues are too complicated to direct anyone to a part to replace. He can install NVRAM at the same time.

Hope you get the satisfaction of replacing the part and seeing it test good.

I vote for the red LED display. It looks good in Diner.

Looks like you need to flip your ribbon cable over at the MPU so that the red stripe is to the right, not the left.

That is correct. If pressing the segment test on the display shows all digits work correctly on the top and bottom display, either that ribbon cable is bad or the MPU. Could flip the ribbon cable at both ends to see if the results change.

result?

Need to see a picture of the MPU below the battery pack to be sure there is no battery damage to U41. Above the battery pack looks great.