System 80 boards are well documented fairly easily repairable.

Aftermarket boards don't eliminate all the system 80 flaws.

Aftermarket boards are generally expensive and are rarely documented well enough to the point of being repairable if something goes wrong.

System 1 MPUs are a different story, since critical parts are unobtainable.

At the end of the day, aftermarket boards are not magic and not perfect.

Unless the original boards are beyond repairing (battery damage on MPU, hole burned through driver board, etc), the originals are fixable.

Originals are ALWAYS preferred.
A lot of folks think that new means better.
If I HAD to choose a S80 aftermarket board, it would be a NiWumpf.
In pinball, that is seldom the case.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball - My YT Channel
http://www.PinWiki.com - The Place to go for Pinball Repair Info

I definitely prefer original. It keeps the game authentic. Additionally, 20 years from now the originals will still be repairable, but that may not be the case for aftermarket replacements. Be certain that any Ni-Cd battery leakage has been neutralized and corrosion damage repaired. Strongly advise the installation of a NVRAM.

My originals look like they've been run over by a truck and are still working and repairable. Well, maybe not that bad, but really have been worked over quite a bit. IMO, just fix them. Once you find and replace any questionable components, they'll be fairly reliable.

Hammerhead This is the first place to look.
Did you replace the header pins?
Reflowing header pins can't really create a reliable connection.
Are the LEDs on the PS lit?
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball - My YT Channel
http://www.PinWiki.com - The Place to go for Pinball Repair Info

What Chris said. A large part of the "unreliability" of my MPU was a very flaky 5 volt connected from the power supply board. I put new square Trifurcon header pins on the PS board, and new connectors into both ends of the power supply harness. Rock solid.

Then something is still wrong on the PS, which should be easy to fix; and again this board is very reliable once properly gone over.

No 5 volts sounds like Q3 went bad, or the legs are not making a solid connection to both sides of the board due to solder not flowing all the way through.

Originals for me too and have fixed a decent pile of them over
the years. The only time I'd go to an after market board is if the
battery puke damage is impossible to fix. But haven't had to do that
yet.

Like I already stated, you may not have flowed the solder all the way through. There needs to be a connection to traces on both front and back of board. Read the PinWiki article about this. Some people use jumpers to avoid the issue.

That sounds like a componet working until it heats up, simply a guess

There's your clue that something still isn't right with these connections. Globbing on more solder is not the answer if there's contamination preventing it from flowing down where it needs to go, or if the trace is broken/cracked on the other side. Like I stated previously, some people install jumpers to eliminate/bypass this kind of issue. Refer to the schematic to know where to connect these legs.

I generally have a short fuse with stock boards, and almost always buy a new one. That said, I am impressed by Zaccaria's CPU & driver boards, so I might try keeping my 2 as stock, except for the horrific Gen 1 power board that is to be replaced as soon as the replacement board comes in the mail.