There's a bunch of information on pinwiki.com about this.

What you've got there is a fix to the wrong part of the problem.

You have to get the daughter board OFF in order to fix it. It's a single sided board and the connections are cracked on the pins on the underside (inaccessible side) of the daughter board. All 80B games have cracked connector pins on this board with exactly the symptoms you describe. It's broken, but you won't be able to see it until you unsolder the daughter board.

It is tedious work to get these boards off. You want to get all the solder off of the pins and have the board pretty much fall out. My soldering skills are OK and I messed up one of the boards I did this on. Patience is key.

I like the replacement boards that Great Plains Electronics sells. They are socketed so they can be disassembled for inspection, and they mount to two sockets on the CPU board for redundancy. They are double-sided so the solder points are less likely to fatigue and crack.

If you have a battery on the CPU board, get it off. If it is a DataSentry battery, it will already be leaking; if it is not, it will be leaking soon. This is a really good idea, but probably not why your game won't boot.

That battery on the board is probably original, not a replacement. That kind seems less likely to leak. Still, it should be removed. I have replaced these with the memory back-up capacitors and they work very well.

If the daughterboard has not been removed and re-soldered, it's not worth troubleshooting anything else. My working assumption is this: every time you move the board, you crack the solder joints more. So what starts out as a flaky problem turns into a consistent problem.

This ALWAYS happens on these games.

Indeed. Disconnect until the CPU works, then replace caps and leave it plugged in. This system lacks a watchdog otherwise.

Please remove the battery from your computer. Fixing battery corrosion is painful and time-consuming.

Minus - side of the cap should measure 0 relative to ground, yeah. 5.05 sounds great.

I don't know why you think the problem isn't in the daughterboard. It's always the daughterboard. They always have cracked solder joints. When they do, the computer won't boot. The symptoms are exactly like what you have now. Even if the problem isn't the daughterboard, it's impossible to tell until it's been confirmed that it's not the problem. And it always sucks, because it's so annoying to work on.

I don't think that work looks factory, by the way. I don't have pictures, but the factory didn't tend to leave flux on it. I would wager that it's hobbyist rework, and it may have been that somebody didn't want to take it all apart, so they re-flowed the joints that they could get at easily. This won't fix the problem.

I really like these: https://www.greatplainselectronics.com/proddetail.asp?prod=140-101 It does two things: first, it mounts to two places on the computer, removing stress and adding redundancy; second, you can just take it off when you want to inspect it.

If you don't want to resolder these (and it IS quite aggravating, even if you have a decent desoldering pump), send it out, and maybe ask for one of the Great Plains boards to be installed.

Great news!

You have a flaky connection somewhere on the board. Check the board carefully for cracked solder connections, or possible corrosion in the battery area. (I had excellent luck with that type of battery. I believe that after the mid '80s most of them were not so likely to kill the board so soon, but rest assured that they will do it soon.)

Batteries leak a corrosive gas, but if the board looks clean, that's great.

Or... stay with me here... it could be that pesky daughterboard has a cracked solder connection. Jiggling it has made it work. Jiggling it again may make it stop.

So be careful. Avoid any shaking, such as earthquakes or a big truck driving by. Do not nudge. In fact it would be best if you avoided any vibration, such as the pop bumpers, flippers, or the ball being kicked into play.