A few thoughts...
Firstly If you didn't already find this website A very good resource for trouble shooting Ms. Pac-Man issues :
http://www.arcadegameover.com/pactrouble.htmlAfter sifting through that you have a few potential solutions :
Did you trace all of the wires from the harness to the correct components, I know it sounds silly but sometimes the smallest dumbest things are the first things to look for. Is the Harness connected properly etc..
If your game doesn't have any sound, and you don't see a picture I would think it's the PCB and not the monitor , could be both especially if you said you were getting the correct power readings from your multimeter. However I'm slightly confused though because you said you see the last screen played, are you talking about burn-in ? It's possible it might just be synch wire, (but it would still be playing blind) since you said a monitor wire was loose. Or the Monitor is in need of repair and potentially could use a cap kit, flyback etc.. I personally wouldn't keep adjusting the monitor especially if you suspect the PCB is bad.. Because you might end up making matters worse.
Just tossing this out there I know someone that does Ms. Pac-Man Board Repairs for a very reasonable 35.00 you just pay shipping both ways. If you want to keep things original..
Alternatively you can also always buy a Pac to JAMMA adaptor and test a random JAMMA game in that cab. Install a 60-1 etc..
http://www.lizardlick.com/Lizard-Lick-Deluxe-Jamma-to-Pac-Adapter_p_118.htmlIf the game has the original power supply , I just installed one of these :

It gives you a newer more reliable switching power supply. Arcadeshop.com sells them, they are 45.00ea called : "Ms. Pac-Man Power Supply Conversion Kit"