Quoted from bwalter:I have this problem with my TMNT Premium: the balls are getting magnetized, presumably by the pizza spinner which is active a lot during typical gameplay. So the auto plunger bracket is putting a small amount of magnetic pull onto the slightly-magnetized ball, which counteracts the energy of the auto-plunge just enough to prevent the ball from launching around the ramp. It may only be some of the balls so far, but it will spread and get stronger.
I bought one of these and degauss TMNT's pinballs about once a month (or more often if I'm playing TMNT more often): https://www.amazon.com/gp/product/B081GG3X7V/ref=ppx_yo_dt_b_asin_title_o05_s00
It takes about ten seconds to demagnetize them all, far less time than it takes to actually open up the machine and extract them.
Makes sense, I've heard about that with games with magnets. The guy I bought the machine from said he had just put 8 new balls in the machine before the sale... do you think it likely for them to get magnetized within 150 or so games? Also, if it's magnetization why would the auto launcher seemingly work well for the first 1 or 2 plunges and then not afterwards?
But regardless it sounds like a worthwhile purchase as even if it's not it, it will probably be something I need in the future. Thanks!
EDIT: Also, do you think something smaller such as https://www.amazon.com/Screwdriver-Mechanical-Electrical-Demagnetise-Demagnetizer/dp/B07H9YC4DJ/ref=sr_1_2 would do the trick or do I need something bigger like the one you linked?