Why did you replace pop bumper (what happened)

Wait a second, back up the truck a bit.

Your diagram shows a fuse that supplies shooter lane feeder, a bunch of ejects, and the kickbacks.
You said your flippers are out, but that fuse is not inline with the flippers. Fuse for the flippers is on the flipper supply board F2. Check for +50 volts at the flipper coil. Put your DMM on DC voltage. Put the black lead on ground (metal side rail of game). Put the red lead on any of the three lugs of the coil. You should get between 50 and 80 volts. No voltage means a fuse is blown, or a wire has broken. Are the flippers still dead?

Checking the switch matrix is no big deal if the machine will boot and go into test mode. Just leave the connectors for all the coil triggers off and go into switch edge test with no balls in the machine. No switches should be registering, then you will know that you have no stuck switches and you can manually activate some switches by hand to assess the overall health of your switch matrix.

Suggest you check these items first and report back.

Yes, the coil should fire when you press the sling in edge test. You should not hear any relays.

The fact that reconnecting the trigger wire shows the sling is active all the time is indicating a shorted switch or diode. Even if it looks good, you'll likely have to measure with a meter. I had a target switch on my F-14 that was shorted internally and I had no choice but to replace it.

Both flippers not working is probably the return to ground path for the buttons and is usually a problem with those connectors@ the MPU or K1 flipper relay. Grounding one side of the flipper buttons with a jumper wire if that fires the flippers for sure is something wrong with that path.

http://pinballrehab.com/1-articles/solid-state-repair/repair-guides/146-switch-matrix-theory-and-troubleshooting

Good page to learn about how to troubleshoot switch matrix problems.

Don't ground the blu-brn wire, ground the transistor tab Q75 to test.

Visual inspection is not good enough. First make sure cabinet button grounds make it back to CPU board IJ19 1 & 2. (ref. pg. 1 of 4 on CPU schematics, pg 55a B1) These connections are not continuous wires either. Both go through the connector 7P1-7J1 (reference cabinet wiring diagram pg 50) You need to make certain K1 relay pulls in and completes ground path from IJ19 1&2 over to common special solenoid ground 2A1. If the relay is not pulling in there could be logic problems on the CPU board - which might explain some of the other locking coil problems but don't get too far ahead with any assumptions until verifying this part of the circuits function. Sometimes in fixing one problem you might resolve the others so see if we can get the flippers working first.

Pops and slings are special solenoids - this is why you might not be seeing a stuck switch for them in test mode:
"The only different between the special solenoids and other system 11 solenoids is how they are activated. Normal system 11 solenoids have a switch on the switch matrix which the CPU monitors. If the switch is closed, the CPU then activates the solenoid and scores the points. The special solenoids can also be used like this too. But they also have an option of having a switch on the playfield that directly controls the solenoid, instead of the CPU. If the playfield switch is closed, this automatically activates the special solenoid's driver transistor, which fires the coil. If this switch gets stuck on, the solenoid coil will lock on or "machine gun"
(from repair guide online)

It's hard to see clearly the detail on the pics, a bit fuzzy even with magnification, looks like there is some problem with the soldering where the legs enter the board on Q77 and Q75. Lack of a fillet visible on the legs of Q77 is a givaway (if you don't know what that means, it's the little mound of solder that is built up between the plated through hole and the component lead)

I'm not saying that it is a cause of a problem because I cannot see the soldering and condition of the traces on both sides of the boards through this picture alone - it may be fine. But just looking at the pic here invites a further investigation. Soldering looks weak on the side of the board, and since these transistors conduct a substantial current they should have a real good solidly formed connection. A resistive connection will heat up during conduction and cause failure to the joint or even burn the board.

Q77 is sitting a little higher from what I see, could be due to being replaced. Q75 middle leg fillet area looks a little dark in the pic. Again, really hard to make out details in this pic and have no idea what the board looks like on the reverse side.

At minimum checking the transistors and those connections for continuity should be done. Another option is to just remove those transistors clean the plated through hole joints and resolder all new transistors so there is no doubt (or very little). The removed transistors can be tested and good ones found can be saved as "emergency" spares. See the section "Transistor Testing procedures, circuit board out of the game." on this guide:
http://hansbalk.home.xs4all.nl/rep/sys11/index1.htm