Black Knight Coil Problems

(Topic ID: 198182)

Black Knight Coil Problems

By tlramey1

10 months ago

Topic Stats

  • 14 posts
  • 3 Pinsiders participating
  • Latest reply 9 months ago by Schwaggs
  • No one calls this topic a favorite


Linked Games

#1 10 months ago

Working on bringing this awesome game back to life. The game blows the F2 coil fuse on power up. I have narrowed it down to something on connector 2J11 on the driver board. I disconnect it and fuses do not blow. I removed all but 1 coil from this connector and the fuse did not blow, but as soon as I add a second coil to the connector it blows the fuse. Basically it seems that any single coil connected to the connector alone will not blow the fuse, but as soon as any other coil is added it blows the fuse.

The coils all seem to be in the 4-5 Ohm range with the exception of the one by the bell. That one reads 14 ohm's. I don't think this is the problem as this coil isn't even found on the connector 2J11 I mentioned above.

I did find a diode installed backwards on the ball ramp kicker coil, but fixing this made no difference. Any help is greatly appreciated.

#2 10 months ago

Do all the coils fire when you turn the game on? When you only have 1 coil connected, does that one coil fire at powerup?

Can you try powering the game up with the connector removed, then plug the connector back in after it starts to see if the fuse blows if you connect J11 after the game is running?

#3 10 months ago

I had a nice, long narrative typed up last night, but fell asleep before hitting send and lost it. Wish this site had auto drafts hang around for 24 hours before self destructing.


I just went through the solenoid firing/locking on issue with my FirePower after years of doing nothing after power-up. BLANKING must be HI for normal game operation.

Remove the solenoid fuse. You don't need it to troubleshoot the logic.

You need to check on your blanking circuit on the driver board. Specifically IC1, IC2, IC3 and IC4. If you look at Sheet 2 of the schematic, there's a horizontal line directly under the PIA, IC5 that says BLANKING. It runs over to the left and joins a black dot and runs on to pin 5 of IC4. The black dot links the signal to the other chips. So while your game is sitting there in attract, probe IC1 - IC4, pins 2, 5, 9, and 13. These must all be HI. Are they?

So with the

#4 9 months ago

Hi Schwaggs. When I fire up the game I do hear at least one coil engage briefly as the fuse pops. I did as you suggested, powered the machine without J11 connected. Fuse did not blow. I added each of the remaining 8 coils back one at a time with the connector disconnected and then connected it after power on, the fuse did NOT blow. I could even start the coil test and it ran through without blowing the fuse. It sounds like you are on to something, what is the next step?

Hi Cody_chunn, It looks like part of your second write up did not make it completely. The solenoids do not seem to have a locking problem that I can tell. I did purchase a repaired driver board and the problem did not change.


#5 9 months ago

Pin 37 of the 40 pin power up should be LO for about 1/2 to 1 second then goes HI.

If it doesn't, perform same test on IC18 pin 4. Is there a 1 second toggle there at power up?

#6 9 months ago

I was thinking what Cody said, sounds like your blanking circuit is not functioning properly or is not connected properly to the driver board. When you power up the game, the blanking circuit should start LOW for about 1/2 a second which gives the CPU time to start up and initialize all the PIAs. The LOW blanking signal blocks solenoids and displays from operating during this period. Before the PIAs are initialized, the lines that control the solenoids and display segments are in an undermined state which could be on or off. As you are seeing, it appears that several of the solenoids are on, which blows the fuse.

Also, the blanking signal in most cases will go low if CPU stops functioning (defective ROM or socket, flaky CPU or socket, etc), preventing solenoids from locking on and/or burning segments of the displays while the CPU is in the locked up state.

Since your game appears to be firing the solenoids at startup, and since you can get the through solenoid test if you disconnect the solenoids for startup and reconnect after, we know blanking is HIGH on the driver board during the startup process when it should be LOW. The blanking signal is generated on the CPU board and as Cody mentions, it is transmitted to the driver board through pin 37 of the 40 pin inter-board connector. If the initial LOW blanking signal does not make it to the driver board through the 40 pin, the pull-up resistors on the driver board pull blanking HIGH at start up. In this case, the usual (incorrect) behavior is several solenoids fire at startup. On some titles, this causes the solenoid fuse to blow, others it does not.

What we don't know is if the blanking circuit is defective (stuck high all the time), OR if the initial LOW blanking signal is not making it to the driver board. The event we need to catch is during the first second, which is tricky as everything happens quickly at startup.

Do you have a logic probe?

Have you replaced the 40 pin inter-board connector?

If you have a logic probe, set it up, disconnect J11 (or pull the fuse that blows) and carefully monitor the signal at pin 37 as someone else turns the game on. You should see it start low, then go high. It happens fast so try it several times.

You can also try the same procedure with the logic probe on the blanking test pin on the CPU board. The blanking test point is just to the right of IC15 and J3 and J4.

If blanking does not start low, the most likely cause is IC23 (556).

Another less scientific (less exact) procedure that may tell us something is to observe the displays during startup. Do you notice garbage on the displays the first instance the game is powered up or do they start blank and in a fraction of a second start with fully formed numbers?

#7 9 months ago

This is great stuff guys. I have a logic probe on the way and will dig in once it's here. I'll post back once i get some more testing done.

#8 9 months ago

J11 disconnected. Looking at the logic probe connected to pin 37 of the 40 pin...power up immediately fires the slingshot coils. I think what I see here is that the probe shows high for the spit second while the slingshots fire, then low, then off. The machine does not enter attract mode. All of this happens within 1/4-ish second. I find that if i power off/on quickly at this point that the slingshots do not fire, and the probe shows low for a moment (no high at the beginning), and the unit goes into attract mode.

IC18 pin 4 on power up goes high and stays there.

#9 9 months ago

Couple things - your initial sentence says the signal goes high, low, then off. As long as the machine is on, you should see either a high or a low signal, you should never see "OFF" (unless you mean low). Also, IC18 pin 4 can't stay high or your displays would not be working.

Does your logic probe have a MEM or Memory setting? Does it have a pulse setting? Can you link or post which one you have? Turn these off for this test if your probe has them.

Try the power on test again with the probe on CPU board IC23 pin 9 or 13 (they are tied together so either will do).

Try the power on test again with the probe on DRIVER board IC4 pin 9.

For each of these tests, you should see the signal at these 2 points be low for 1/4 to 1/2 a second, then stay high.

Have you replaced the 40 pin inter-board connector recently? After running the tests above, can you loosen the mounting screws on your CPU and Driver boards, slightly pull the boards apart at the interboard connector (1/4 inch or so will do) and push them back together, screw them back down and see if the solenoids still fire at startup.

#10 9 months ago

You Guys nailed it. IC23 replaced, fuses no longer blow at power up. It looks like i have the battery issue where it powers up with the 2500 4 in score 1 and 04 00 in the credit area. It seems the fix is swap the on-board batteries for off-board due to the leakage issue. I was lucky and none of the boards in this one show any sort of damage due to acid. I'll save this for the coming weekend.

Otherwise, the tests for the solenoids seem to be working. The sound portion of the diagnostics do not work. No sound coming from the unit, though turning up the volume controls makes the speaker hum. Pressing switch 1 on the sound board puts out some sort of tone that stays on until I turn off the machine.

Else the only other issue that I know of is that the right flippers do not fire. All flippers worked when I first powered on the game, but now only the left functions. Would the culprit likely be the relay on the driver board labeled frl-264? Any way to test before I swap it?

If I get through the remaining issues, I will be ordering replacement play field inserts as many of the ones in this play field have warped to the point of cupping.

#11 9 months ago

Awesome progress!

Remote battery holder is a great idea. Alternately you can get a 5101 compatible NVRAM.

When you try the sound test, try adjusting the sounds/voice balance control that is on the voice board (the smaller sound board) in addition to the main volume. Make sure you have the two 4 pin connectors at the top of the sound board in the right places. If all that looks OK, make sure the ROMS are installed correctly and try reseating all the ROMs and the CPU. Check the sockets to see if they are loose.
Make sure the DIP switches are set correctly - SW1 OFF and SW2 ON.

For the flipper issue, seems unlikely the solenoid would be the culprit although it certainly is possible. A separate wire leaves the driver board through J12 for each flipper side, pin 1 (right) and pin 2 (left). J12 is the second connector from the top on the left side of the driver board. Pin 1 and 2 are the bottom 2 pins. I would start with that connector. Check the header pins for cold solder joints. Check that the wire is making good connection with the IDC connector.

#12 9 months ago

Battery now working.

Sound partially figured out. I found a step-by-step from cody_chunn and followed that to the output of IC10 pins 2-9. Bad IC10. I get the self test results as expected, but when I press the actual self test button on the sound card it goes through the other sounds ok, yet the voice sounds like it's speaking backwards. All of the words are out of order. Prior to working on the flipper below I started a game and no sound. No sound, no speech. More tshooting here I can tell.

For the flipper, I found pin 1 in connector J12 actually melted inside the female side....the plastic was bubbled. Guess I will be replacing the whole connector. I'll check the right side flippers for shorts, diodes, etc before powering it up again.


#13 9 months ago

update on the vocabulary issue, read the manual!

#14 9 months ago

Check the all the header pins on both boards for cold solder joints. Probably not a bad idea to reflow and add just a touch of solder to each pin. Replace the header pins on J12 or any other connector that was overheated.

Sound control signals come from J9, the bottom connector on the left side of the driver board.

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