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Sunday 13 May 2018 at 07:32
2N4401 is the predriver transistor. (Zacaj mentioned it in his post)
Note the TIP122 transistor can be substituted by the more 'robust' TIP102 transistor. I keep both TIP102's and 2N4401's in stock for my BK.
Good luck with the fix--my buddy's BK was doing the same thing a while back and replacing ...
Source: http://pinside.com/pinball/forum/topic/williams-black-knight-blowing-solenoid-fuse#post-4395221