(Topic ID: 234624)

Star Trek Pre Fuse?


By newpinbin

8 months ago



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  • 26 posts
  • 3 Pinsiders participating
  • Latest reply 8 months ago by G-P-E
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ST Prem Chart (resized).jpg
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#15 8 months ago
Quoted from newpinbin:

Ok it was the Q12. Part is in ST is back!!!!!!!!! 100% Thanks for your help. My friend did the re solder for me.

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.

#18 8 months ago

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.

#26 8 months ago
Quoted from robertmee:

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.

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

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