Here is the diagram for ST Prem Flippers. There is a misprint in manual calling out two Upper Left flippers, so not sure which one is the right. You'll have to determine by wire color at the fuse...GRY-YEL or BLU-YEL.

Try this: Power off of machine, replace fuse, remove connector J9 from board. Meter on Ohms/Continuity. Black lead on Ground Strap. Red lead on either end of GOOD fuse, do you read a short or 0 ohms? If not, then replace J9 and do the same test. Now do you read short or 0 ohms?

As a comparison, do the same tests on a working flipper to see if they are different readings.

Also, you can check the coil itself....remove the fuse and J9, meter on ohms, and measure the resistance across the two coil lugs. Compare to a working flipper (don't forget to remove fuse for the working flipper).

ST Prem Flipper (resized).jpg

Which test is reading 0...the last one with J9 and the fuse removed? Did you compare the same test to the working flipper?

Sounds like your coil shorted. Replace it.

Good deal....Figures Stern's diagram is wrong. The Diagram shows Q14, but I see from the chart in the manual it's Q12. Not only that, they got the connector wrong too...J8 vs J9. Hard to know what to believe without standing in front of the game.

Anyway, glad you got it figured out.

ST Prem Chart (resized).jpg

You want to be careful, and not apply high heat to the pads for very long. Do you have a decent soldering iron that's temperature controlled or just a 15W pencil heater? Definitely don't use a solder gun as they're too hot. For desoldering, clip the transistor off the board so you're dealing with only one leg at a time. If you're unsure of proper desolder and re-solder techniques, best to get a friend to do it that is, or practice on an old board first.

Congrats!

OK --- that's progress but you're not quite completely out of the woods yet. Check the back-EMF diode (tied from coil to +50V). If it's bad (open) - Q12 will fail again.

On a Stern ST? I don't think flipper coils have diodes on them. They're on the board aren't they? Admittedly, never owned a ST, but just going by the Stern Manual. But yeah, he can check it on the board. However, in another thread, he mentioned that held the flipper up for about 3 minutes to show someone something, and that likely blew the transistor.

Yep, whenever there are controlled coils then there has to be back EMF diodes. They are shown in the drawing in post #3 above.
He mentioned the blown transistor. *Something* took out the transistor and there is a good chance that a bad diode can do that.

When you hold a ball with the flipper on this particular machine, it is pulsing the coil to hold it. This is turning on and off the transistor in rapid succession causing a no-stop stream of back-EMF pulses.

Yeah, we get that....but your post said tied to the coil, which isn't the case...diodes are on the board. That's all I was clarifying.

Ed is correct that it doesn't hurt to check the diode....I think it's D12...it'll be right near the Q12 transistor. Remove the J connector for the coil and with power off, Meter on diode, you should see .6v with meter leads one way and open or OL with leads reversed across diode.

Same as a transistor...desolder and solder a new one. But check it first.

It would still operate, but if the diode is bad, Q12 could be damaged again.

OK, OK... it is *electrically* tied to the coil which is what I was alluding to.