The power supply board in there may be the wrong one, mine looks like this. Not saying it can't work like that, but is a possible hack and I can't tell what value that fuse should be by the schematics.

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Your pic looks like the inside of my Blackout. You might have an earlier Black Knight than mine that had older board sets in it. If your transformer is in the head instead of the cabinet than this is the case and that fuse is a 2.5 amp slowblow that is listed as +28vdc Solenoids.

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Also replied via e-mail, but figured I'd post it here too....

Thomas;

That fuse is a 2.5A slow-blow fuse, and is your solenoid fuse. If a machine is being troublesome, it tends to blow out a lot, so I'd buy a bunch of them if I were you.

Yours is an early production Black Knight, and has the System 6 style power supply in it. The CPU board is a system 7, just the power supply is system 6. Honestly, It's a good thing, as the later System 7 power supplies had major issues with burning connectors for the GI lighting.

The connector with the red/brown wiring on it goes to the relay which controls the GI lights. Normally the GI lights are always on, but there are certain times that the game flashes them too, which is what that relay controls.

-Hans

Radio Shack

Changing the capacitors is fairly easy, getting hold of them is a bit tricky as they are uncommon pieces these days.

Great Plains Electronics and Big Daddy Electronics are the two best sources for them.

-Hans

Yes, you have a System 6/7 hybred same as my BK. Nothing unusual.

The power supply from the looks of it has the original 1980 caps in it. That makes them 33 years old on components that were originally spec'd for about 5.

Just like grandma then dry out with age and start to act weird.

http://www.greatplainselectronics.com/proddetail.asp?prod=W36-PEC-KIT

Is the kit you want. Ed has them marked as currently out of stock but if you manually piece the kit together or give him a call he will substitute the one cap he is having source problems with.

OK, you are dealing with exactly the same thing I just fixed on mine. The connector in question goes to the driver board that triggers the special relay that triggers some of the lights on the game. This relay gets it's power from that fuse that also powers some of the game's solenoids including the trough. Yes my wire was broken,too. After repairing the wire and 40 pin connector, the game was still intermittently locking up and blowing the fuse. In the end I was able to replicate the problem by lightly flexing the boards until I found the spot on the driver board that had the bad connection. On mine it was the upper right driver plug with all the green wires that go to the switch matrix. There was a bad connection on the board under the plastic where you can't see it. I re-soldered it from the back side and now it's fixed. The fuse is a 2.5 amp slow blow for the solenoid circuit. I hope this helps. It was frustrating.
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Good luck! Not saying this is your problem too, but it's worth installing a new fuse, starting up the game and wiggling this connector. If that brown wire was hitting ground, it may also blow that fuse.

That is a diode, the electronic equivilant of a back flow valve. It does look kinda crispy, and at only pennies each worth replacing. Observe polarity (which end the stripe is on)

Well if the coil and fuse seem good the switch is a logical place to go. Does the switch register in tests?

Are you using a ball to check the switch, or just your finger. Always use an actual ball, for both safety and accuracy reasons. Switches do not have separate fuses, and usually a wiring issue in the switch harness will cause multiple switch failures, as they share wires between each other.

To check the coil, set it to check ohms of resistance. Between the two lugs on the coil, it should see about 3 ohms or so. You should also be seeing about 30 volts on the coil lug with the two red wires attached.

-Hans

I'm gonna let Hans finish this one off, he's the man and helped me with mine, he'll have you up in good time.

You can't really see it with your eyes, but those are insulated wires. They have to be, or the coil would be one big, fat, dead short.

Did you check the coil's resistance?

set your DMM to the lowest ohms setting. Touch your probes together to see what a short reads.
It could be from 0.0 to 0.5 VDC due to the meter or the probes used.

Now measure right across the diode soldered to the coil terminals.
What Ohms reading do you get?

Reverse the leads and measure again for Ohms.

A few reasons it could be doing that. Most often on a system 7 is the 40pin interconnect, or more accurately the solder joints. Williams had started using the RN sockets at that point which were better than the SCANBE stuff, but do fail from time to time.

-Hans

May not be a bad idea. Lots of little nuances to those early Williams boards. Enough that I built a business around repairing them. Once you work on them a lot it becomes second nature, but it's a lot of little things to get used to it.

-Hans

I was nearly to the point of sending mine out when I dove in shotgun style. Replaced interconnect, reflowed all connectors (and I mean all on every board), replaced every cap on all the boards, replaced most of the IDC connectors with molex, and upgraded lamp resistors and transistors. Like Hans said, these boards are old and tend to have lots of little things going on. Took a couple days of soldering at the bench, but plays like new now. If I can do it so can you, but if you send out then Hans would be the guy to send to, like I said he knows his stuff and is a good guy. If you decide to dive in here is some good info...
http://pinside.com/pinball/forum/topic/vids-guide-to-bulletproofing-williams-system-6

Replacement boards should only be used as a last resort to replace a missing or totally fried original. Power boards are the easy ones to fix/rebuild. It sounds like more going on than the power board anyway. I went through 2 boxes of those 2.5 amp solenoid fuses before I got it all worked out. Rebuild the interconnect, even if it looks ok. Mine looked OK and even tested good with a meter. Reflow your connectors and recap everything. I'm betting that will do it. Caps and connectors are cheaper than a new board that most likely won't solve all the problems. That interconnect is the likely culprit.
My $.02
From Vid's thread...
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Xpin makes a Great power supply. Them and kohout are the only ones I'd buy.
However, I can't tell you how many times I've seen people say "I replaced the power supply and its still not working". Don't get me wrong, the modern replacements are far superior to the original design, for a few reasons. It's just that it likely isn't the source of your problem. The originals are pretty bulletproof already. That being said, I have an xpin power supply myself, soon in both of my machines. They run cooler, use less power, and have a better rectifier circuit than the system 6 design.

Nothing is a bigger source of problems than connectors and sockets on these machines, you'll almost always see resoldered headers on the boards. Bad battery holders is the #2. Heat realted component failure on the driver board is #3. (This excludes user created problems such as bad solder work or blown transistors from over fusing the solenoids)

+1 on that. I spent my time last night doing just that on a Hyperball.

Again, my BK now works perfect after resoldering the switch matrix connectors on the back side of the driver board.

That worked for me.

Sometimes it works to just re-heat them, but if there's too much oxidation it potentially can make things worse. If possible I always suggest to remove all the old solder and apply new, but I also recognize it's not always possible to do that.

Hard to tell without very good close-up photos, but the driver board doesn't look too bad, I don't see any obviously failed solder joints in there.

How does the back of the CPU board look?

-Hans

My solder joint failed where you couldn't see it. Under the plastic connector.