If the pop does not fire during test, but fires when you ground the metal tab of the transistor then you have a CPU board problem.

Do you have a logic probe or a voltmeter?

Ok, testing like that does not confirm that the wiring back to the CPU is good. Grounding the transistor ensures good wiring and board connector.

So this means you have a break between the transistor and the coil. If you find J-19 connector on the cpu board and remove it. Then take your ground wire and touch it to the blue/yellow wire in the connector does the pop fire?

There are some large and small molex connectors that are for disconnecting the play field. Find the one that has the blue/yellow wire. See if the wire has pulled loose or that one of the pins has popped out of the connector. These connectors are hanging below the back box.

I think you should post a pic of the pop. Green/yellow wire should go to points switch. The coil should have 2 18 gauge red/white wires and a 22 gauge blue/yellow wire.

Different wire but to me it still looks like a blue/yellow wire.

Yes most likely does. Can you find the connector with this wire on one side and the darker blue wire on the other side. Make sure that the pins in the connector haven't come loose and are pushed out the connector housing. If they look good then separate the connector and use you meter to test each side for continuity. Let me know what you find.

How did you do the test?

Try it again using a jumper wire that is connected to ground. Touch it to the metal part of the connector.

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This is the problem with intermittent connections, you check for continuity and it's good. Then you try to apply current and the connection opens up. So somewhere between J-19 and the coil there is a break. You can separate the molex connector under the back box and then reconnect it to see if that helps. You can connect the ground jumper to Q-69 with a alligator clip and then move the blue/yellow wire around looking for the break. You can also run a new wire if nothing else works.

It is possible, but then you would have 2 issues at the same time. If you want to test it with the ohmmeter you can. Place the game in coil test and stop on the pop coil. Place red lead on the J-19 connector blue/yellow wire and black lead on the ground braid. As the CPU pulses the coil the meter will flicker just like if you were to touch the meter leads together then separate.

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It could be a number of things, Q-69, Q-68, U-45, R-94, R-95, U-49, U-38 and cracked solder joints. You can test with your voltmeter.

Pretty standard issue for this older pin. The divertors usually melt down too.