Welcome! You found the right place for help.

So all 3 of the pop bumpers aren't working, and at least one other switch. Have you tried activating the slingshots (the triangular bumpers above the flippers)? I ask because they share the same circuit as the pop bumpers and if they aren't working either, that may give us a clue. Also, how about the 'S' target? Does that score when activated?

Do you have experience opening up the playfield? I ask because the next thing i would check is the fuse under the playfield. You might actually be able to see it and possibly reach it through the coin door. It's usually fairly close to the area the flippers are, and it's usually a 1-amp slow blow/MDL fuse. See if you can locate that fuse, pull it out and check it for continuity with a meter. If you don't know how, i can help.

Starting to suspect none of the solenoids are firing except the flippers...

Sounds like you may have a bad transistor on the Solenoid Driver Unit (SDU), causing that pop bumper to lock on. I'd open up the backbox and look for a fried transistor on the SDU (the transistors are toward the bottom of the board)... The fuse was blowing because of the pop bumper locking on... Higher rated fuse is allowing the pop bumper to remain locked on, which is why you caught a whiff of the magic smoke (the 1A fuse was cutting it off before it could start burning stuff up)...

Thanks for the pics, that'll help us troubleshoot this further.

Even though it says the right pop bumper is #9 on the chart, that chart is referring to the pop bumper activation switch, but not the coil itself. Checking the schematics, it looks like the right pop bumper coil is controlled by Q14 on the SDU. Screenshot_20201203_130027_com.google.android.apps.docs(1).jpg

Those other burned up areas could certainly be from previous repairs.

Do you have a multimeter? If so, the transistor can be checked using the diode test function. Let us know if you have a meter and we'll take it from there. If not, it's time to get one

I would pull the board out of the game for testing, it's easier to access everything and get the meter probes in the right spots.

You were on the right track testing the transistor with your meter in diode test, but here's the exact procedure for testing them:

On the top side of the board, put the black lead of your meter on the metal tab of the transistor you're testing. Keep the black lead there while testing the following:

Put the red lead of your meter on the center lead of a transistor. Your meter should read zero.

Put the red lead of your meter on either outside lead of a transistor one at a time. Your meter should read in the .4 to .6 volt range.

Put the red lead of your meter on the other outside lead of the transistor. Your meter should again read in the .4 to .6 volt range.

If your meter reads anything outside the .4 to .6 range, replace that transistor

Note that this test isn't 100% accurate, as they can sometimes test good even when they're bad. However, if it tests bad with the meter you can pretty much rest assured it's bad. You can always compare readings with other transistors nearby too. If you decide the replace the transistor, it's recommended to use a TIP102 as a substitute for the SE9302 transistors that were originally installed.

Good luck, and share your findings! Ask any questions you run into along the way, too.