Look for cracked solder joints on the MPU.

If everything checks out there, you may need to replace the RAM chip.

Edit: wait, if it says memory ok, then the RAM is likely fine. What is the exact wording on the screen?

Do you see an actual error message or just a checksum?

Does it actually say "error" or does it just say that the checksum is 2603?

If it does actually say error, try re-seating the game ROM chip on the MPU. Also try carefully cleaning the legs with a pink rubber eraser if they look tarnished or black.

That should be fine then. That's not an error.

Can you start a game?

When you put in the new coil, did you make sure the wires went back onto the same lugs and the diode was facing the same direction?

A checksum is just an algorithm to verify the contents of the PROM to make sure that it's not corrupt. Essentially, it's the PROM saying "the contents of my chip equals 1234 if you do this algorithm" Then the computer says "Let me prove it. I'll do that algorithm that's based on your contents, if true, will equal 1234." Then the programming runs the algorithm and says "Yea. Looks good. Your checksum is 1234." Or, it'll fail the checksum test (say the instead of the answer to the algorithm being 1234, its 8530), which means that the contents of the PROM have been corrupted for whatever reason.

TL;DR: Your game displaying a checksum isn't an error. It's just displaying the results of an algorithm to verify the contents of the prom chip. No worries there.

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Do System 3 games daisy chain the power to the solenoids? It could be that when you replaced the solenoid, you didn't solder something in properly, like Forceflow mentioned, and broke power to the other solenoids in the chain.

Check fuse F26. Looks like that bridges power to the 3 up kickers.

Does F26 blow in addition to F27?

According to the schematics, F27 covers all three coils, and F26 is behind that which covers only the left and right upcickers.

So, if you are still blowing only F27, then you're still having an issue with only the center upkicker.

Your 311 color-coded wire (the wire with the orange-brown-brown stripes) should be connected to the coil lug that has the unbanded side of the diode. If the orange-brown-brown wire is connected to the lug with the banded side of the diode, you will need to swap the wires that are on each lug--the orange-brown-brown on the unbanded side, and the two wires that are twisted together need to be on the banded side.

Ok, also take a look at the left and right upkickers to make sure those have the correct wires on the correct lugs.

The left upkicker should have the 300 (orange-black-black) color coded wire on the unbanded side.

The right upkicker should have the 322 (orange-red-red) color coded wire on the unbanded side.

If you had tbe coul hooked up backwards most likely you blew a transiator somewhere.