Q: Coil Strength

[lothian]

I read lots of good information about flipper coil issues within this forum and others. Poor flipper performance typically indicates a problem with something other than the coil because coils rarely go bad and never get weak. This statement seems to be the consensus among those knowledgeable of technical pinball stuff, with the additional insight that coils rarely burn out or become weak by themselves and they likely got that way because something broke upstream in the circuit. Fine.

So with all that out of the way... I have a spongy flipper; meaning, when a ball smacks an "up" flipper (cabinet button depressed) the flipper curtseys noticeably while its mate does not.

When I press this flipper in the up position it just [If]eels[/I] spongy. I checked the usual list of mechanical whatnots and none are the cause. Voltage to the coil is 25v, though I think it's supposed to be 28v? Lower-than-required voltage would make a coil weak, wouldn't it? But would three volts make that much difference?

I'm definitely new to working under a pinball playfield, so I have zero idea what is an "ah HA!" or a red herring. Am I on the right track?

 

[Chris Bardon]

Which games is this on? Might help diagnose. If the left/right flippers are the same coil, I might try swapping them to see if the problem moves? If the flipper isn't holding up, then is it too tight/loose to the PF? There should be a little bit of up/down movement on a flipper (I think the rule of thumb was around a business card's thickness). Sometimes if they're too tight, there's too much friction and they don't flip well, and don't return to neutral well either. Game manual should probably say what the voltage to the flipper should be, but again, measure left/right and see if there's a difference. If they're the same coil strength, then they should probably be the same voltage as well.

 

[lothian]

Williams Black Knight.

In the interest of brevity, I left out the miscellaneous t'shooting whatnots I've done so far. I swapped the coils and the problem persisted. I replaced the bushing and set the flipper-to-playfield gap with a credit card. The flipper shaft is secure in the flipper and the clamp. Manual shows 28v--the coil is getting 25v while the high and low winding resistance values are in spec.

 

[MrMikeman]

Coil sleeve and EOS switch gap would be the next 2 things to check.

 

[lothian]

Coil sleeve is in excellent condition.
EOS switch gap needs further inspection...

 

[sylvain]

Just curious, what was the fix to your earlier bottom flipper flutter?

Re: for your new question, flipper spongy & 'curtseys':
- As others indicated, this is often caused by a worn sleeve, or mechanically misaligned
- and/or a mushroomed solenoid bottom causing drag inside the sleeve
- wrong coil number
- wrong return spring
- EOS pitted or wrongly adjusted
- for 'curtseys': could be angled or mushroomed coil stop, and/or mushroomed solenoid bottom

 

[Chris Bardon]

I swapped the coils and the problem persisted.

So when you swapped the coil, the problem was on the same flipper with the "good" coil, and the flipper that had the "bad" coil was OK? If that's the case, then it's likely not the coil. Sounds like you've tried a lot already. I'm not actually sure whether a 3v drop at that range makes a significant impact, but there could be something upstream that's causing the voltage to drop. Do those boards have test points on them? You could see if the voltage is low coming off the board? If both of the flippers are wired direct to a board, and it's not too much of a pain, I might actually try swapping the connectors to reverse them, and see if the problem moves. No idea if that's possible on a BK though-I've never owned anything pre-WPC, so haven't had to troubleshoot much on older games. You've also got the upper flippers to deal with there, which I'd assume are wired in sequence with the lower ones, so moving things might not be possible.