Williams Black Knight Blowing Solenoid Fuse

http://www.marcospecialties.com/pinball-parts/SA-23-850

Hello everyone! Been an arcade guy for several years, just got into pins a few months ago. I recently acquired my second pin, a Williams Black Knight. Still working despite minimal maintenance over the years.

I noticed that some of the drop targets weren’t working properly. They had issues falling without being hit 2-3 times. I pulled all the assemblies, took them apart, cleaned everything, added new springs for the targets, and new coil sleeves. At first, everything worked great, then I noticed that the left lower and upper drop targets were having trouble resetting. It may take them several times to pop back up, scoring points each time they tried and didn’t.

I assumed that the coils were weak, so I ordered new ones. Here’s a link to what I purchased:

I installed the coils yesterday, turned the machine on, and none of the solenoids worked on the table! Just the flippers. I looked in the back box, and the 2.5A fuse had blown. Fearing that I had somehow ordered the wrong parts, I put the original coils back in, replaced the fuse, powered on, and fuse immediately blew. I found that the only way that I could keep the fuse from blowing was to disconnect the solenoid power connector (located under the 2.5A fuse.). As soon as I tried to reconnect, the fuse would blow again.

I need some troubleshooting help. I have all the tools to check things(Multi Meter, Logic Probe, Soldering Station, etc.), but I have no idea where to begin. I’m assuming that the issue is something under the playfield possibly? Please help, and thanks in advance!

#2 5 years ago

ZAC

zacaj

If you disconnect those coils, does it still blow?

If so, try unplugging 2J9, 2J11, and 2J12. If it doesn't blow then, reconnect them one at a time to narrow down which solenoids are causing it.

Test the transistors for the coils you replaced, see if they're bad

#3 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
If you disconnect those coils, does it still blow?
If so, try unplugging 2J9, 2J11, and 2J12. If it doesn't blow then, reconnect them one at a time to narrow down which solenoids are causing it.
Test the transistors for the coils you replaced, see if they're bad

The connection I’m referring to that I’ve unplugged is connector 3J3 on the power board. If I unplug it, the fuse doesn’t blow. I’ve not tried unplugging the ones on the driver board and leaving the Solenoid Power connector plugged in. I can give it a try, but I only have two fuses left, and the others I’ve ordered won’t be here till Saturday. Gotta be careful!

Also, I’ll test the diodes and see what they measure.

#4 5 years ago

ZAC

zacaj

OP
Quoted from kingofpain79:
The connection I’m referring to that I’ve unplugged is connector 3J3 on the power board. If I unplug it, the fuse doesn’t blow. I’ve not tried unplugging the ones on the driver board and leaving the Solenoid Power connector plugged in. I can give it a try, but I only have two fuses left, and the others I’ve ordered won’t be here till Saturday. Gotta be careful!
Also, I’ll test the diodes and see what they measure.

Grab a circuit breaker from the hardware store and connect it in with clips. If it's blowing a slow blow that fast a higher rated circuit breaker will blow too, and then you can just reset it.

Can also do a quick check on the transistors, just test resistance from their tab to ground. Should be near infinite when the game is off. If any are blown it'll be pretty low.

My first guess is that you might have wired one of your coils backwards.

#5 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
Grab a circuit breaker from the hardware store and connect it in with clips. If it's blowing a slow blow that fast a higher rated circuit breaker will blow too, and then you can just reset it.
Can also do a quick check on the transistors, just test resistance from their tab to ground. Should be near infinite when the game is off. If any are blown it'll be pretty low.
My first guess is that you might have wired one of your coils backwards.

Any suggestions on circuit breakers? Only hardware store close to me is Lowe’s, and they are all of the 15-20Amp variety. Sorry for the newbie question!

I will check transistors and report back.

Also, I thought I wired the coils back correctly, but I could have gotten them backwards. Any way to check that to be sure?

#6 5 years ago

ZAC

zacaj

OP
Quoted from kingofpain79:
Any suggestions on circuit breakers? Only hardware store close to me is Lowe’s, and they are all of the 15-20Amp variety. Sorry for the newbie question!
I will check transistors and report back.
Also, I thought I wired the coils back correctly, but I could have gotten them backwards. Any way to check that to be sure?

I'd remove the diode and check it. If it's blown that'd confirm that they'd been backwards. If it's not they may still have been, but no other way to really tell.

#7 5 years ago

KOP

kingofpain79

Inactive member

So I wanted to post a quick update:

I removed all the Solenoid Drive connectors from the driver board, hooked the Solenoid Power connector back up to 3J3, new fuse, and powered the machine on. Fuse didn’t blow. I then started putting the Drive connectors back, and when I got to 2J11, the fuse blew. So my issue would be in those sets of coils it seems?

#8 5 years ago

ZAC

zacaj

It looks like 2J11 covers all the drop targets, so one of them is probably still the culprit

#9 5 years ago

KOP

kingofpain79

Inactive member

Also, I tested the diodes on both the new coils, one is dead. The other is .4 Ohms. So yeah, I got something wired backwards it seems. Just got to figure out where.

#10 5 years ago

ZAC

zacaj

OP
Quoted from kingofpain79:
Also, I tested the diodes on both the new coils, one is dead. The other is .4 Ohms. So yeah, I got something wired backwards it seems. Just got to figure out where.

I'd replace the diodes on both coils, double check the wiring, check the transistors for both coils

#11 5 years ago

KOP

kingofpain79

Inactive member

Ok. I’ll get that done in the next couple of days and I’ll report back. Thanks for the help!

Quoted from zacaj:I'd replace the diodes on both coils, double check the wiring, check the transistors for both coils

#12 5 years ago

JON

Schwaggs

Gameroom Mods

10y 105K 4,760 10

You need to check the wires on the solenoid. You need to get the correct wire on the correct terminal. It isn’t important left and right terminal, what matters is that the power feed wire(s) is on the banded side of the diode that is on the coil. The terminal on the non-banded side of the diode is the driver transistor side of the coil is always a single wire and is typically smaller diameter.

Also check you physically installed the coils in the correct orientation and the terminals are not shorting out to other metal pieces.

#13 5 years ago

KOP

kingofpain79

Inactive member

Quoted from Schwaggs:
You need to check the wires on the solenoid. You need to get the correct wire on the correct terminal. It isn’t important left and right terminal, what matters is that the power feed wire(s) is on the banded side of the diode that is on the coil. The terminal on the non-banded side of the diode is the driver transistor side of the coil is always a single wire and is typically smaller diameter.
Also check you physically installed the coils in the correct orientation and the terminals are not shorting out to other metal pieces.

Thanks for the info. I checked my wiring for the coils, and they are indeed wired correctly. Power on banded side, driver on non banded. I measured the resistance of the diodes, and they all check out as good. I also checked the transistors in the back box for the Solenoid drives, and they all checked out good as well.

Since I know that the issue has to be a drop target coil, I was thinking about unhooking each one, and wiring them back up one at a time till the fuse blows. That should help me isolate the issue right?

#14 5 years ago

ZAC

zacaj

OP
Quoted from kingofpain79:
Since I know that the issue has to be a drop target coil, I was thinking about unhooking each one, and wiring them back up one at a time till the fuse blows. That should help me isolate the issue right?

That should help. Disconnect them, and as long as the fuse doesn't blow immediately anymore, try just touching the wires to the coils while it's on, see if the coil fires or you get any spark. You might get away with firing it once without the fuse blowing

#15 5 years ago

DIK

someotherguy

Pinside member

6y 44,150 419

Something to keep in mind is coils don't get weak, they either work or they don't. If they get stuck on they can melt to the point the bobbin plastic can distort and cause the sleeve to be too tight on the plunger. If there's no damage like that then the issue with resetting properly can be incorrect springs, crud in the coil sleeve/on the plunger (someone tried lubing it in the past; these are meant to operate dry), or crud in the plastic sliders/on the edges of the targets (again with the lube being a problem, or old playfield wax.)

Besides the circuit breaker, another way you can prevent wasting fuses as you troubleshoot a problem is a normal household light bulb and socket. Wire it up to some alligator clips that you can hook into the fuse holder. If there's a short, the bulb will light up - instant visual indication vs. wondering if the circuit breaker has tripped.

As you can see in the attached pic, I have a 100W bulb in a porcelain base, alligator-clipped to the solenoid fuse position on the power supply. The lit up bulb is telling me there's a short...without killing fuses in the process.

Richard

bulbtest (resized).jpg

#16 5 years ago

KOP

kingofpain79

Inactive member

So I wanted to post a quick update;

I unhooked the left upper and lower drop target coils, turned the machine on, and the fuse didn’t blow. Turned the machine off, hooked up the upper play field coil, turned machine on, and fuse was good. Hooked up the lower play field coil, turned machine on, and fuse blew.

Switched the coil out for new coil with fresh diode(tested good), hooked it back up with power on banded lug and driver on non banded lug, turned machine on and fuse blew again.

So I now know that the lower left drop target coil is causing the issue. Any suggestions now?

#17 5 years ago

ZAC

zacaj

Next thing I'd do is replace transistor and pre-driver for that coil if you haven't already

#18 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
Next thing I'd do is replace transistor and pre-driver for that coil if you haven't already

Ok newb question time. I’m looking at the manual, at a diagram of the driver board. I’m guessing that Q17 is the transistor that I should change, since it’s labeled for Solenoid 2, lower left play field drop targets. Where’s the pre-driver located?

#19 5 years ago

ZAC

zacaj

It's the 2n4401 that's connected to the input of the transistor. In the case of Q17, it's Q16. They tend to be one off number-wise, but that's not 100%. On the driver board physically they're located right above the transistor, but below the resistors associated with it

#20 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
It's the 2n4401 that's connected to the input of the transistor. In the case of Q17, it's Q16. They tend to be one off number-wise, but that's not 100%. On the driver board physically they're located right above the transistor, but below the resistors associated with it

I gotcha. Got a part # for the transistor? The manual I’m looking at doesn’t list it...

#21 5 years ago

TPR

frunch

Pinside member

Point Pleasant, NJ

11y 135K 3,635 10

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 those 2 transistors took care of it.

#22 5 years ago

KOP

kingofpain79

Inactive member

Quoted from frunch:
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 those 2 transistors took care of it.

Thanks for the info. Time to order more parts! I’ll get those replaced and report back. Hopefully it will do the trick.

#23 5 years ago

KOP

kingofpain79

Inactive member

Ok, so I got my parts in the mail today, installed the transistors (drive and pre-drive.), powered the machine up, and it seems that the coils are now not getting any power. Plus, I can’t seem to start a game. Any suggestions on what to check now?

#24 5 years ago

ZAC

zacaj

Check switch test for start button, fuses, voltage at coils

#25 5 years ago

KOP

kingofpain79

Inactive member

Ok, so I have an update finally. So I went under the play field to test voltages. All coils are getting 33VDC consistently EXCEPT for the coil for the drain hole, under the apron. It’s only getting .6VDC, and when I drop a ball in there to activate it, it moves but barely. Also, I noticed that the Solenoid fuse tries to blow during this, but doesn’t. It glows orange in the center every time it tries to activate.

So I’m assuming that I need to look at the driver/pre-driver transistors for that coil next? Maybe a new diode for that coil as well? Here’s a YouTube link showing the fuse in action.

Also, can anyone explain the menu numbers in diagnostic mode? I can’t seem to find anything detailing this in the manual, unless I’m overlooking something.

#26 5 years ago

ZAC

zacaj

Disconnect the coil, check its resistance. Check the voltage on the wires detached from the coil. If it's still low, you've got an issue in the wiring.

#27 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
Disconnect the coil, check its resistance. Check the voltage on the wires detached from the coil. If it's still low, you've got an issue in the wiring.

Ok. Resistance at the coil unhooked is 4.5

Voltages still around .6 to 1VDC

So how exactly do I check the wiring at this point?

#28 5 years ago

ZAC

zacaj

OP
Quoted from kingofpain79:
Ok. Resistance at the coil unhooked is 4.5
Voltages still around .6 to 1VDC
So how exactly do I check the wiring at this point?

Trace that wire back, see where it goes to previously. At some point there must be proper voltage. Maybe the wire is broken or a bad solder joint

#29 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
Trace that wire back, see where it goes to previously. At some point there must be proper voltage. Maybe the wire is broken or a bad solder joint

Ok this is really weird. I checked continuity for both of the power wires at the drain hole coil, and both checked out fine. I soldered them back, and they are now getting 33VDC. However, that coil still won’t work! I checked and the kicker is moving freely in and out of the coil. So what now? Also, I can’t get the game to start with three balls loaded up either.

#30 5 years ago

ZAC

zacaj

Wiggle the wires a few times and see if the voltage stays. Could be a break in the wire.

Does grounding the transistor tab for the coil work?

Do all the trough switches register fine in switch test?

#31 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
Wiggle the wires a few times and see if the voltage stays. Could be a break in the wire.
Does grounding the transistor tab for the coil work?
Do all the trough switches register fine in switch test?

Voltage stays when wiggled.

Not sure how to do that....

And not sure which mode in diagnostics is for the switch test.

In the coil test mode, I found that the fuse glows a little orange every time a coil fires, and if I hit the skirt for the pop bumper enough, the fuse would blow. Seems this is a bigger issue than I realized.....

#32 5 years ago

ZAC

zacaj

You sure you've got the right fuses? I can't think of anything that would cause this for all coils

Switch test is the one after coil test. It should blink the lowest numbered closed switch on one of the displays. take out all the balls and make sure all the drops are up, then load balls into the trough one at a time and make sure all three switches register. Check the manual for a better description of it.

To test the transistor, locate it on the driver board. According to the solenoid table the outhole is #6, Q25 or Q14 depending on your driver board. There's a diagram of the driver board in the schematics with each solenoid number's components laid out, so locate the transistor on your driver board using that. Then, take a piece of wire and momentarily connect the metal tab with a hole on it on the top of the transistor to the metal back wall of the head. This should bypass the transistor and ground the solenoid. If the solenoid fires, you have a driver board problem, otherwise there's a wiring issue.

#33 5 years ago

KOP

kingofpain79

Inactive member

Quoted from zacaj:
You sure you've got the right fuses? I can't think of anything that would cause this for all coils.

2 1/2 Amp Slow Blow fuse correct? That’s what the manual says anyway. I’m pretty sure that what I got. I’ll double check tomorrow to make sure.

I’ll check the switch test tomorrow and see if I can get coils to fire with the grounding method. I’m about to beat my head against the wall here! And I know it’s got to be frustrating for you too, but I really do appreciate you taking the time here!

#34 5 years ago

KOP

kingofpain79

Inactive member

zacaj I am so sorry, but you are correct. I do have the wrong fuses!!! When I ordered them, I got .250A 250V / (1/4amp) Slow Blow 3AG Fuses, instead of what I really needed. I have no idea why I did this, but at the time the numbers made perfect sense to me!!!

I have ordered the correct fuses, and they should be here in a few days. I will report back with the results after I get them. Thank you for being patient and helping me. I did learn some troubleshooting techniques, and they will be beneficial to me in the future.

Geez! How embarrassing!!!

#35 5 years ago

KOP

kingofpain79

Inactive member