Picked up a Royal Rumble last week, and after setting it up the game played fine for about 10 games, and then a lamp issue appeared. Going through single lamp test I was able to confirm that more than half of the lamps was lighting other lamps. There might be more patterns, but the main two I identified were:

-any lamp in row 3 will light lamps in rows 1,2,3 of that column
-any lamp in row 2 will light lamps in rows 1,3 (but not 2) of that column
-any lamp in row 4 will light lamps in rows 4,5,6 of that column

This didn't sound like a lamp matrix issue since it was affecting every column. If it was always extra rows, I would have assumed I have a row-row short somewhere, but I can't figure out how that would result in the correct row not lighting. So I figured it was probably a board issue, most likely in the PIA or logic ICs between the PIA and the row transistors (a pair of 7406 inverters). I disconnected the lamp connectors from the board and then hooked up my logic probe and checked the outputs of the 7406s, and found that, with a lamp in row 4 lit, I was seeing activity on all three of the pins associated with rows 4-6, and none elsewhere, so this confirmed to me that it was a board issue with one of the chips.

I removed the two 7406s and replaced them with new ones (socketed), and also swapped the PIA for a known good one, and put the board back in, but it didn't affect the issue. A bit confused, I then removed the 7406s and read the outputs of the PIA, and again the pins for rows 4-6 were all strobing while the rest remained stable. This didn't make any sense, as I knew the PIA was good. I swapped it back into another board and confirmed that it was still good. According to the schematic, there outputs of the PIA do nothing besides connect to the 7406s, and since they weren't installed, there shouldn't be anything else affecting the outputs.
Data_East_1994_The_Who_s_Tommy_Pinball_Wizard_Manu_2017-10-23_19-33-53 (resized).png
Data_East_1994_The_Who_s_Tommy_Pinball_Wizard_Manu_2017-10-23_19-35-10 (resized).png

Now I was at the point where I couldn't explain what I was seeing, so I went nuclear. Unplugged everything not necessary, rechecked all chips out of circuit, verified the game rom was correct: nothing. So I swapped the board with my Tommy, and the problem stayed with Royal Rumble. Went in again with the probe, and confirmed that I was getting the same wrong signals on the Tommy board in WWF (even with the lamps unplugged!), and that the WWF board in Tommy was no longer showing them. I disconnected all the 555 lamp boards on the playfield, and the problem is still there. I tested every remaining lamp diode on the playfield, and they're all fine. Checked for shorts to ground and 18V from every row+column, nothing. Checked continuity between every row and every column on both the playfield and the board connector, nothing.

Not sure where else to look at this point.

EDIT:
as an additional test, I put the Tommy ROM in the Royal Rumble (disconnected all coils just in case), and then went through lamp test, and all the lamps worked fine. Then I put the RR ROM in Tommy, and went through the lamp test, and all the lamps worked fine. But RR ROM in RR has the issue.

I'll put in an order for some blanks, worth a shot...

That's what I'd think, but then why does the RR rom in the RR board in Tommy work fine?

It seems like there must be something wrong with the rr rom and the rr game which are combining to cause this but I can't imagine what it could be

Didn't mention, but this was all done with sound card unplugged. Needed display to get into display test

Other interesting thing I noticed while playing Tommy (with rr board still in it) today: I could swear the CPU is running 'fast'. The high score initials move way quicker than they used to, it seems like the attract light show is going faster, and the autolaunch during multiball is firing before the ball had a chance to settle onto the kicker, so balls aren't clearing the lane sometimes.