Black Knight
Williams, 1980Dear gurus, sleuths, diagnosticians, pinball detectives, doctors and medics,
I have a Black Knight which was fine and now is not (same old story). The game boots up and goes into attract mode, I can add credits but not start a game. I have no solenoids working in the coil test.
I checked fuse F2 (removed it and used a multimeter) it is most definitely good. Where to now?
Any help greatly appreciated, SV.
Quoted from zacaj:Do you have voltage at the coils?
Thanks Zacaj, I only have a tiny bit of voltage at the coils, 0.6V.
Quoted from solarvalue:Thanks Zacaj, I only have a tiny bit of voltage at the coils, 0.6V.
You'll need to trace that back through the chain of connections etc and find where the problem is. Hopefully you have voltage at the rectifier? I think from there, it goes into the power supply board, through the fuse, out of the board again, and then through the playfield-head connector.
Check the bridge rectifiers in the back box.
Maybe a good time to add the Bridge Board to make it safe.
No more burning hazard with a Bridge Board....
http://home.kpn.nl/p.koch3/
Available at Big Daddy Enterprises, Marco Specialties (USA) and RTTB (Australia).
Or order with me when in Europe.
Peter
www.inkochnito.nl
Quoted from Inkochnito:Maybe a good time to add the Bridge Board to make it safe.
No more burning hazard with a Bridge Board....
Thanks, looks great but I already have the fuses installed.
Measure the voltage from F2 to ground.
If that is good, measure at power supply P3 pin 6
If that is good, trace the wire from pin 6 to the connector between the backbox and lower cabinet. Make sure that connector is solid.
Quoted from Schwaggs:Measure the voltage from F2 to ground.
OK, same 0.6V at F2 and at the positive terminal of the solenoids rectifier.
It turns out that the 8A SB fuse has blown (I have the extra fuses installed before the rectifiers). Should I go ahead and replace this fuse or does that mean I need to do something else as well?
Quoted from solarvalue:It turns out that the 8A SB fuse has blown (I have the extra fuses installed before the rectifiers). Should I go ahead and replace this fuse or does that mean I need to do something else as well?
Test the rectifier, it could have failed internally.
Quoted from zacaj:Test the rectifier, it could have failed internally.
Do I have to remove the spade connectors to test it? It looks like they have been soldered on.
Quoted from solarvalue:Do I have to remove the spade connectors to test it? It looks like they have been soldered on.
I've never tried it when it's connected still, not sure if you'll still get good readings. Mine always had the spade connectors for easy removal.
Simple way to test it: put in a really low value fuse (1A fast blow), unplug the power connector going into the PSU (6J1?), and then just fire it up again. If the fuse blows, it's definitely bad 
Quoted from solarvalue:It turns out that the 8A SB fuse has blown (I have the extra fuses installed before the rectifiers). Should I go ahead and replace this fuse or does that mean I need to do something else as well?
Last time i had one of those fuses blow, i replaced the rectifier and fuse...that fixed it. I didn't even bother testing the bridge (bc i was in a hurry), but i figured i should replace it since it was the original bridge. Working fine ever since...
Quoted from solarvalue:Do I have to remove the spade connectors to test it? It looks like they have been soldered on.
If the fuse blew, you likely have a shorted bridge. Shorts will test short in or out of circuit. Test each pair of legs in the diode setting and if you get 0.0v, you found the problem. If not, properly test each pair of legs in diode setting- should read open one way, and 0.4-0.6ish with the meter leads reversed.
The game not starting is likely a separate issue, unless you meant that the game starts you just can't play (without solenoids).
Quoted from solarvalue:Do I have to remove the spade connectors to test it? It looks like they have been soldered on.
No, you can pull the (blue) connector.
Just to seperate the bridge rectifier from the transformer.
http://www.ipdb.org/showpic.pl?id=310&picno=16006 (lower right corner).
Black Knight has 2 magnets.
Together with the flippers.
All on the same cirquit.
Perhaps the 8A fuse is a bit low.
The manual calls for a 20A fuse at F4.
F4 is supplied via the bridge rectifier, which you fused with a 8A fuse.....
I've had this one time when someone installed one of my Bridge Boards in a Black Knight.
I advised him to put in a 10A or 12A fuse.
Maybe even higher if this does not work during game play.
Just test every coil (flipper and magnet) seperatly with a 8A fuse, to make sure they are working correct and are not shorting.
Then you can up the fuse value for the bridge rectifier.
The rectifier can handle 35A, so a fuse like 15A would not hurt.
The fuse before the rectifier is there to prevent the wires from burning up when it goes bad.
Peter
www.inkochnito.nl
Quoted from Inkochnito:No, you can pull the (blue) connector.
Just to seperate the bridge rectifier from the transformer.
Thanks, did that, and the rectifier checks out OK, so I just replaced the fuse.
I have other problems, but I have a separate thread for that:
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Rochester, NY
Piershil