Upon powering up game the led display flashes 0 and the two led's light then display and led's go out. Pushing lower diagnostic button nothing happens, pressing higher button the 0 and the two leds come on but as soon as it is released, the display and the leds go out.

That sounds perfectly normal. Since the numeric display isn't getting stuck at a number, we can assume the board is running.

With the game running, measure the voltage at Test Point 4. This is the blanking signal. It should be 5V if all is good.

Also make sure the CPU and driver boards are physically mounted correctly.

All is not good. No voltage at TP4, unless I am not grounding at a proper location. I have never tested at a test point before. This new problem didn't happen until I replaced the Q6 transistor, which makes no sense to me. I only removed the driver out of the backbox to do it and never even removed the CPU.

Any ground point should work. So if Blanking is held low, that would explain the main displays going blank....

Make sure your boards are mounted correctly. Specifically, the CPU board should be resting in the mounting slot at the lower edge of the board. Each board should have a couple mounting screws installed (helps with grounding).

Some replacement 40 pin connectors end up with a little more sticking out of the board which if the 2 boards are pushed too tightly together at the 40 pin connector can short out to the brackets. Try separating the boards (without disconnecting them) just a touch to see if anything changes.

Okay. I will try when I get home. My back box does not have the middle support between the CPU and the driver. I had made a small block of wood just for support back there but maybe I should remove it just in case. And try to find an actual support.

Okay. I will try when I get home. My back box does not have the middle support between the CPU and the driver so I made a small block of wood just for support back there but maybe I should remove it just in case. And try to find an actual support.

So I just removed my CPU and driver boards and removed my wood support from behind. I have made sure the driver and CPU aren't crammed together at the 40 pin. I reinstalled with the same result.

Looked in the manual (paper) and at ipdb and cannot find post and rubber list for BK. I see only Marco has red fin posts. Are the ones used in BK the 1" and 1-1/8" posts?

1"
https://www.marcospecialties.com/pinball-parts/C-951-7

1-1/8"
https://www.marcospecialties.com/pinball-parts/C-952-7

Good evening everyone,
I'm in need of some help. I've been having issues with the 2 ball lock not firing in game or in test mode so I checked the transistors and Q28 was reading kinda funny so i replaced it with a 2n4401. on power it smoked the new Q28 so i thought maybe the coil or the diode were shorted so i removed them and everything checked ok , but when i went to put them back in i realized that the previous owner had put the wires on backwards so i correctly wired the coil up and replaced both Q28 and 29 and now it dosent instantly smoke Q28 it does work but now Q28 and Q29 get HOT like burn your finger hot. The coil is warm but it dosent look like the coil is on. if i put a ball in it kicks it out and the eject pin retracts and i can repeat the process again and again. eventually it will start smoking if i let it go long enough. i also checked all the resistors R51 reads 68 R50 reads 553 and R52 reads 2.7K i did check a few others in the area and they all read similarly with the exception of the 2.7k is only 1.7 K on R43,R46,R49. So is something stuck on or did i not use the correct replacement for Q28 ?

Thanks Bruce

Could someone point me to where this wire needs to go?

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My guess is that is one of the ground wires and goes underneath that wing nut in the middle front, under those wires in that picture.

That is exactly right. It goes under the wing nut with the ground braid.

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Thank you!!

Its the ground for the magna save. The magnet won't work unless these are connected.

Looking for guidance on where to start. My Black Knight has been working well for months. Lifted the playfield to replace a burned out bulb on the underside of the playfield, and now none of the solenoids, except for the four flippers, are firing. Thinking I might have crimped a wire or jostled one loose during the playfield lift, I eyeballed each solenoid and surrounding areas and did tug tests here and there....nothing obvious. Since 1-24 went out all at the same time, there must be a common area to start (I do not have a schematic, but I do have a MM but not sure where to probe). Anyone have any guidance? All fuses, including F2 for the solenoids, look intact.

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With the game off, pull the F2 fuse and measure with with a multi meter. A visual check is not good enough

Taking the fuse out of the game and getting a closer look, it doesn't look healthy. And mm shows 0....blown. Dang it...I should've caught that. Thank you, @eh97ac. Not going to find a replacement on Christmas Day, so the family will have to settle for ST Pro and EBD tonight.

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OK...plot thickens. Turns out I do have spares (I bought a BK fuse replacement kit months ago and forgot about it). Replaced the fuse and the solenoids worked for about 2 minutes and then the new fuse blew. Replaced it again, worked for about 2 minutes, and then that one blew. Ideas for narrowing this down?

Arrgh. Thought I could go thru the coil test one by one and see which one(s) are causing the fuse to blow, but the F2 fuse is blowing before I can even get to the coil test. I'm not starting a game at all...just turning on and going straight to self test. Gotta be a short somewhere but not sure at all how to proceed with the triage. Any ideas?

You may have to work with a mm and check each part associated with that fuse to make sure it is properly connected. You can check continuity and for amp/volt at the solenoids but you may have to unsolder a wire or both off the coil to take it out of circuit.

You sure one of your slings or pop isn't locking on? Pull 2j13 see if it stops blowing

Sounds like you may have a coil locking on when you turn the game on (due most likely to a bad transistor on the driver board). Listen carefully for the sound of a coil activating and humming when the game is turned on, and prepare to turn the game back off shortly after to hopefully spare the fuse. Zacaj is right on the money as usual, pull the connector he mentions and see if the problem persists. One other tip: knock down drop targets from each bank just in case if the coil that's locking on is one of the drop target reset coils. If any banks immediately reset when you turn the game on, you'll know it's the corresponding drop target reset coil that's locked on. That's exactly what happened to my buddy's BK, and it was a matter of replacing the driver and pre-driver transistors and the diode on the drop target reset coil to fix it. Good luck!

Alright so a few weeks ago I posted as well about a stuck coil, the pop bumper on my BK. I have since replaced the transistors at both Q5 and Q6. Prior to replacement the coil would lock on instantly the moment the machine was turned on. When I replaced the two transistors and turned the machine on for the *FIRST TIME*, the coil was NOT stuck on. I figured the problem was corrected. I tried playing a game to test the game and the moment the pop bumper skirt was hit the coil stuck on again. I immediately turned the machine off. After that the coil was permanently stuck on again. After that initial power-on, every single time the machine is turned on the coil locks on immediately when the machine is turned on, just like before. I removed the Q6 transistor from the board so I could power the game back on without the pop bumper coil locking on. I ran a switch diagnostic. I noticed that when the pop bumper skirt was pressed while in diagnostics, switch 36 (pop/jet bumper) would not register as ON. Aside from that everything else in the machine works perfectly. Someone had suggested that the culprit may be IC6 or IC8. If it were one of these IC's wouldn't an entire row or column in the switch matrix fail? Maybe I'm mistaken but it seems that if it were an IC issue it'd be incredibly unlikely for ONE single switch/coil to fail. Where should I go next here? Replace IC 6 and/or 8 or is there something else more likely? Not to sound lazy but I'd prefer to exhaust all of the easier-to-fix potential issues before cutting off and replacing IC's on the driver board which is a huge pain.

Thanx, @frunch and @zacaj....I'll be trying that sometime tomorrow after I venture out and pick up some more 2.5A fuses. I did have something interesting happen with my very last spare fuse tonight if it helps....I followed the coil wires as best as I could without actually clipping the ties holding the harness together and didn't see any nicks or cuts in the wires leaving it exposed for shorting out. I did move the wire harness around a bit during the inspection. I decided to try my last fuse, and sure enough it started working. I ran thru the coil test and manually fired each one 5 times...worked like a champ. I started a game and played 3 complete games with multiple 3-ball multi-balls going on in each of the games....everything worked. Somewhat satisfied but a bit concerned that it appeared "fixed" after simply handling the wire harness, I propped up the playfield so that I could re-attach the apron, put the playfield back down, powered on, and F2 blew again.

I'll try pulling 2j13 and the drop target reset tip after I pick up a few dozen more fuses and report back. Thanx again....

Special solenoids don't register in switch test unless they fire. The skirt is directly connected to the driver board (via 2j13), and when the pop actually fires the mechanism closes a secondary switch to actually register the points.

Doesn't this circuit get disabled by a relay while in attract mode (along with flippers) ? If that's the case then it couldn't be the switch on the flipper skirt shorted, right? Otherwise it wouldn't be locked on in attract mode.

It only enables during a game or test mode

If that's the case then in what possible scenario could the pop bumper coil lock on the instant the machine is turned on (and in attract mode)? Even if Q6 were shorted or an IC were defective the coil should only lock on when a game is started and not in attract mode due to the relay that disables that circuit in attract mode, no?

The relay only enables the flippers. The rest are enabled via logic chips, so technically they, or the transistor, could still be bad and cause a lock on in attract mode.

Ok thanks for the clarification. I guess I'll be swapping out ic6 and 8.

Also, while I'm not sure if this could possibly have any bearing on your problem Moses_1592, I'd also recommend checking the wiring to the pop bumper switch. The pop bumper switch also has an electrolytic cap and resistor. Make sure the wiring and the leads from the cap or resistor aren't touching anything they shouldn't be. If they're original parts, you may want to change them out too...

When you lay the playfield down, lugs from a solenoid aren’t touching anything they shouldn’t be are they?

It happened to me once, took me a while to figure it out... I had a lug barely touching a part close to the plunger, and it kept popping a fuse.

Had my CPU and Driver out and on my bench tester with my Leon's test ROM. Ultimately I ended up doing a reset and put the boards back in. Diagnostics button works properly and flashes "0" with the two LED's and then "0" and LED's go out. Again while crediting a game, the jet bumper locks on. I just pulled the driver and replaced the IC6 with a new 7408. Reinstalled and it still locks the jet. I have a new 7402 I can install. Is there a way to test the 100 ohm resistor and the capacitor on the jet bumper switch (could that be a possibility)? Dang I want to get this up and running, I just got a CPR replacement plastics set for Christmas I need to install.

The cap and resistor won't do anything if 2j13 is removed, so I don't think they're the issue

Well I have now replaced IC8 with a new 7402 as well, and it is still locking the jet.

I haven't read the whole thread but have you replaced the diode on the coil? Is it the right way round?

Yes, the coil diode I replaced. Stripe faces the red power wires. I didn't have a IN4001 diode on hand but I did have a IN4003 diode that I used.

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You can easily test the capacitor, just put your meter on resistance (ohms) and test across the cap with the power to the game off and the red lead on the plus side of the capacitor. If it is good, you should see a low resistance that increases over time. If it is bad, you will see a constant low resistance (close to zero).

Stupid question but it is hard to see from the pictures - the switch on the spoon is gaped ever so slightly open with the skirt at rest and the terminals of the switch are not touching, right?

Nothing stupid Jon. I have quadruple checked it, and it is not touching or closed. I'm still thinking I am overlooking the most basic issue. But it has not reared its ugly head. I will confirm the capacitor tomorrow.

I just tested the capacitor on the jet bumper. I am getting an increase up to 5.06 - 5.07 ohms either side I test it from. I also tested the slings since they are the same capacitor and I am getting the same reading.

Regarding my similar coil issue, I did some exploring under my cab last night and noticed the coil diode on the pop bumper coil vibrated loose from the solder on one of the lugs. I read in another thread somewhere that on this era Williams machines, without the coil diode intact (to prevent voltage spike) on a special solenoid that one single pulse of the pop bumper coil could essentially fry the driver transistor. I did indeed notice that when I replaced the TIP 102 and turned the game on for the FIRST TIME, the coil was not locked, but the moment the pop bumper skirt triggered the coil it immediately locked on and was permanently locked on thereafter, even after shutting the machine off and turning back on. After this happened I tried yet another brand new TIP 102 and the exact same thing happened, no lock until the coil was triggered once, then it was stuck locked on. I figure I just fried 2 brand new TIP102's.

I haven't had a chance to replace the diode, but does this sound like a plausible explanation for my problem?

Finding a 2.5A SB fuse locally proved fruitless - nobody carries them where I'm at (Lowes, Home Depot, Ace Hardware, Radio Shack Express). All were happy to order me some, but no one stocked them. Pack of 10 arrived from Amazon today so I resumed troubleshooting.

- All coils moved freely when testing by hand. None stuck.
- None of the four target banks reset at power on.
- Before I tried pulling 2j13, I decided to do the following:

I thought back to when this started - I lifted the playfield to clean a contact in the turnaround (it would register a ball going thru about 50% of the time). After cleaning the contact and putting the playfield back down, that's when F2 started blowing. I went thru three fuses without moving the playfield. Then I lifted the playfield again to inspect coils and coil wires. In that process, I moved a cable harness around and put the playfield back down. I went thru the manual coil test one by one, all firing correctly. I lifted the playfield again to retrieve a flashlight I left in the cabinet (too far back to reach thru the coin door) and re-attach the apron, put the playfield down, and F2 blew again. This was all on Tuesday.

Flash forward to today now that I have some more fuses. I thought about the correlation between the cable harness moving and the solenoid fuse blowing coupled with knowing that none of the coils are stuck and all seem to be free-moving. I took a closer look at the cable harness location and decided to route it to the left of the transformer next to/on top of the cage instead of leaving it hanging/dragging on top of the components next to it (see photo). Since doing that, the game has played for 2+ hours without an issue, and I've lifted and laid back down the playfield several times. Note: the transformer has a very noticeable "hum" to it...pretty loud when you first turn the game on, then quiets down within a couple seconds, but still significantly louder than my EBD machine. Transformer looks original.

Next step is to rebuild/replace the transformer, but in the meantime BK is back to being playable.
Wiring Harness Move 02a (resized).jpg

I have just replaced the capacitor on the jet bumper switch. I have even adjusted the switch so it doesn't contact even when the spoon is depressed. Upon trying to credit a game or going into diagnostics it locks the jet. I now adjusted the switch so that it has continuity with my DMM. The other thing I did was trim the end of the score switch for the jet bumper because it looked fairly close to the spring and I know @Crispin had an issue with his Black Knight with the end of the switch grounding out on the spring. Not sure how, but it is not locking the jet bumper anymore. But it also isn't working. I have retested Q6 and Q5 and they both test good. I can play a game, but again with no jet bumper working.

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To anyone interested, correcting the disconnected coil diode fixed the problem. If that diode goes bad or is disconnected it will immediately destroy the driver transistor the moment the coil is triggered.

Does the pop bumper coil fire in coil test? If so, you know the driver, coil and wiring is good and can focus on the switch side of the mechanism.

It does not fire in coil test. Sorry, forgot to mention that.

What screw or post goes here? I took pics of tear down, however I don’t see it in mine. I think it is supposed to hold this guide, and I’m missing it.

Thanks!

image (resized).jpg

image (resized).jpg

It has a nail

Huh.... what is a good replacement, nail or otherwise? I’m not sure on size/length, but I can swing by the HW store tomorrow.

Excited to play! I took apart the drop target mechs on the upper pf, and man were those dirty.