Some thoughts on left VUK problems and adjustments.
Oddly the left VUK does NOT have a schematic, exploded view or parts list in the manual.
So, its impossible to get the correct replacement parts without this important information!
My incorrect plunger as noted above was installed (I think) because the prior repair person didnt have the parts list and did the best they could.
I have included the left VUK schematic from Pinball Resource at the end of this post. The same document has been posted before on a couple other "Weak Left VUK" threads.
Its important that the VUK has a plunger that's not worn out, missing the metal cap on the end or worn and dragging coil sleeve, and has the correct spring. Too strong of a spring makes the mech fail (the williams 10-135 common spring was too strong).
If you look at the mech, you can physically bend it left or right while its bolted in the game.
If its not perfectly square to the playfield, you should bend it so that it is. A little bending is a lot. So just make very slight adjustments on this.
If the end tab of the mounting bracket (that has the rubber grommet in it) is bent outwards, you should bend it square to the bracket. If this is bent to far out, the plunger will rest too low and weaken the throw of the ball.
The idea is the get it to shoot a ball straight up the center of just very slightly to the right, so the ball can ride up without dragging or getting spit out to the left and rolling back down the horus lane.
One of the biggest complaints about this mech, is that when the game is under a high load it takes several tries to feed the ball. This can cause abnormal wear to the plunger, coil sleeve, spring and drive transistor.
If you rebuild the mech, make certain that the plunger moves exactly straight up and down. Its possible to have the plunger move at a slight angle if the coil brackets are crooked or set off center. This causes the ball to rattle in the chute.
I press the brackets firmly onto the coil and firmly and to one side while tightening the screws. Both the top and bottom brackets should align to the same side. It can be easy to be off a little and have the plunger shoot at an angle.
Replacing the coil with a stronger one is also one of the solutions. There is a bally coil (BF-27-1250 must add a diode) that is "Really close" where you want it to go as far as power, however you must add a diode to it. You can see it listed on the coil resistance chart.
Ideally you need an "in between" sized/powered Gottlieb coil that doesn't exist.
By removing 2-3 ohms (200 or so turns) of wire, the coil is quite a bit stronger (and basically make the Bally coil without buying one). But not so strong as to bounce the ball off the top deflector, and have it roll back down onto the mech. My coil reads 13 ohms without the diode, 13.5 ohms with the diode in place.
With the modified coil, the mech is strong enough to clear 2 balls at once and not "fail" to eject balls when the game is under full load.
IMHO its really perfect now.
Here is the Left VUK schematic with the part numbers, that isnt in the manual:
VUK schematic (resized).jpg