Black Knight - weird sound issue

robert16

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Hi all,

I've owned a Black Knight table for a dozen years or so. I've recently been restoring it to full working condition, and I have one weird problem left. Right in the middle of a game, the sound will just get all weird. It won't respond to game events and will play a solid tone, sometimes with some static-y sounds behind it. Sometimes it'll jump into the sound test. Usually if I switch it off and back on again and run the sound test, it'll pick back up and work normally. But it's really annoying when it happens in the middle of a game.

I've looked at the physical components on the board and nothing looks damaged or burnt. Both fuses are good and the board is properly grounded. The intermittent nature of it is strange to me. If anyone could tell me where to start looking, I'd appreciate it. Thanks!

Robert
 
Have you pressed the diag button on the sound board to ensure all the sounds will play correctly?

I had a ton of issues with my Defender years ago and it was all sound rom related, once I stuck the roms in an EPROM burner and compared the checksums, it was obvious something had corrupted them (age likely).

Once you've verified the sound board itself and rooms are likely good (clear sounds), use the diag mode of the machine itself to cycle through the sounds and see if they all play well.

Corrupt or missing sound after a while of playing sounds like a heat issue to me, something is getting warm back there and hitting thermal shutdown (pretty common on old IC's). A can of freeze spray is always handy to trying to isolate the spot or simply using a moistened finger to quickly feel chips etc (careful, if one is really hot you'll know quick lol).

If you have full GI lighting running in that back box with light bulbs and not LEDs, it gets insanely warm back there. Could also try playing with the GI lights off or removed and crack the back box open slightly, if it plays longer than normal then it almost certainly points to a heat issue.

Let us know how you make out!

Cheers
Tim
 
Hi Tim,

Thanks for your response. I have tried the diagnostic button, and when it's working, all sounds play correctly. When it's not, it's the same weird noise. The heat thing actually makes a bit of sense. It happened the other night when I'd just left it on in "attract mode" for like 6 hours. The sound finally cut out after all that time (even though I wasn't playing) and wouldn't straighten itself back out until the next morning (presumably after it had cooled off).

Vents in that backboard are obviously limited. Is there any way I could rig up a small fan to that board and direct the hot air out of the cabinet (at least a little)? Where is the best place to steal some power if I were to try that? And I'll definitely try replacing the bulbs in the back glass with LED's and see if that helps. Of course I just played two games and everything was fine so I haven't been able to test it, but it at least now I have a starting point.

I'll definitely post my findings when I know more. Thanks again!

Rob
 
Rob:

Make sure that the large footprint chips (processor, PIA, ROMS) on both your sound and speech board do not have any black tarnish on the chip legs. If so, GENTLY remove them and clean the legs with a fine grit sandpaper, 400 grit recommended. This may help some of your phantom/intermittent sound issues. good luck.

Chris
 
Okay, I realize it's been a while since this thread was active, but I finally got some good info about what's causing my sound problem. It's definitely not an overheating problem. It happened the other day in the beginning of my first game after not turning it on for two weeks. I even checked and every single chip on the board was cool to the touch.

I did notice that it always happened during the big events in the game, like the start of multiball or the resetting of a couple banks of drop targets. Usually all it would take is a press (or two or three) of the diagnostic button on the sound board to fix it. The first two clicks of the button would change the sound to some other weird noise, but not fix it. Then eventually, a 3rd or 4th click would reset it to the correct set of test sounds. Subsequently, I was able to start a game with the sound working properly, and just jiggle the little switch back and forth (without pressing it) and the sound would flake out. Power off, on, and proper press of the switch and it would come back.

Now...the question is...does this make sense to anyone? And what can I do about it? Thanks in advance for any ideas!
 
Resolder the header pins on both the sound board and the MPU board and see if your problems go away. You may need to repin those connectors as well. If they are still the original IDC, they are probably loosing their tension.

The sound is linked to that game in very interesting ways. I was having a similar issue and this is what fixed it.
 
I realized I forgot about this thread, so I figured I'd put a bow on it now and share my solution.

craigmack was nearly right. It wasn't the connectors or the header pins, but one actual wire was bad. There are two connectors that must be attached from the main cabinet. Both have three wires, one is a wide connector with gray, striped cables. The other is narrow, with a black, red and a (for me at least) insulated braid of wires. I'm not sure if this is standard issue for this machine, but those wires had become frayed and could co longer carry a consistent signal. I rebraided them and wrapped them in some electrical tape, and voila! All better. I've played a few dozen games and the sound has been perfect. A pity to fret so much over a small thing like that, but if anyone out there is as bad as I am with electronics, maybe this post will help you! Thanks to everyone for good ideas...
 
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