(Topic ID: 173198)

When one coil is connected, others fire randomly


By jcar302

3 years ago



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  • 11 posts
  • 3 Pinsiders participating
  • Latest reply 3 years ago by jcar302
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#1 3 years ago

Ok, I know I have another Williams fire post, but it won't let me adjust the title.

Long story short.
Q22 was shorted and the bell and knocker wouldn't work.
Changed the transistor and replaced the diode on the fire bell coil.
Now when I connect the bell coil (it has a plug) seems like switches and other coils fire each other with no rhyme or reason during coil tests and game play(there probably is one, I just don't know it).
For example, the bell rings on about 25% of switches. So if I press the flipper buttons, it rings, score some points, it rings.
Same goes for the ramps going up and down (although with other switches, not the flippers)
Even as you rack up points it causes the coils to kick the balls into the shooter lane and things to happen.

Unplug the bell coil? All goes back to normal.
Not sure where to look.
Thanks,
Joe

#2 3 years ago

Do all the coils and flashers fire correctly in test mode?

#3 3 years ago

sounds like an a/b side issue. The bell is allowing power to get to the side that should be turned off / not selected.

shorted isolation diode? I forget exactly off the top of my head how the a/b sides are wired.

#4 3 years ago
Quoted from zacaj:

Do all the coils and flashers fire correctly in test mode?

In test mode with the bell coil connected, all coils work when they are supposed to, but most (not all) set off the bell. It's not nearly as hard as when the bell actually goes off though. Most times it's much more less hard.

Disconnect the bell, everything tests fine.

Bara, i'll have to check into the isolation diode, not sure what or where that is.

Thanks for the reply's.

#5 3 years ago

Check to see if the knocker is energizing at all as well, that might help narrow it down.

If you look in the manual (http://mirror2.ipdb.org/files/859/Williams_1987_Fire_Instruction_Manual.pdf, PDF page 64) it's got a diagram of all the coils. Each flasher and coil has a diode between it and their common drive transistor, so if one of those is letting current go backwards then lots of strange stuff can happen. Not sure where the isolation diodes are located in the actual machine though...

#6 3 years ago
Quoted from zacaj:

Check to see if the knocker is energizing at all as well, that might help narrow it down.
If you look in the manual (http://mirror2.ipdb.org/files/859/Williams_1987_Fire_Instruction_Manual.pdf, PDF page 64) it's got a diagram of all the coils. Each flasher and coil has a diode between it and their common drive transistor, so if one of those is letting current go backwards then lots of strange stuff can happen. Not sure where the isolation diodes are located in the actual machine though...

I think in F-14, there is a PCB under the PF with a bunch of diodes on it, fire probably the same. Check for the common wire color there and see if the diode connected is shorted.

#7 3 years ago

Ok thanks guys,
I think you have me on the right track.
I took this board out
Bottom left A on diode test reads continuity
I think it says it's an n5401. I don't have one of these, is there a replacement at radioshack?
Edit: since radio shacks site sucks, I re-searched for a 1n5401 and it comes up as in store only. I'll stop tomorrow.
The rest read between 460-560

20161110_165447 (resized).jpg

#8 3 years ago

Those look like 3 amp diodes. You don't have to be too specific on part numbers. Get a standard rectifier diode that will fit and is rated at least 3 amp and at least 100v.

3 amp and 6 amp diodes will probably be able to fit. 1n5401 to 1n5408 is an acceptable replacement part numbers to look for.

#9 3 years ago

Ok, radioshack had 1n5402's so I got them on your advice.
Soldering on a wide open board is so much easier than on the mpu.
All is good, everything works right.
Thanks guys.

#10 3 years ago

nice! thanks for following up that was the fix.

have fun

#11 3 years ago
Quoted from barakandl:

nice! thanks for following up that was the fix.
have fun

I always follow up on any forum. Nothing is worse than when you find something in a search and these is no conclusion.

This is one of the few hobby forums I belong to that I have more questions than answers, so i'm always appreciative.

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