Black Knight solenoid lock-on issue, intermittant.

HHaase

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This is getting annoying, and I'm slowly going through everything that I suspect, but I figured as I'm stuck at work and can't test anything right now, I'll throw a post up here.
I've got a Black Knight, which occasionally works at about 90%, with a couple non-important things not working at all such as a couple lights and the bell ringer.

But it's only working intermittantly. The rest of the time, solenoids #1 through #8 all lock-on once I try to play, which blows the fuse. I'm not even sure what I'm doing that makes it temporarily "work". Here's what I've done so far.

Replaced all the male pin headers on the driver board.
Replaced the interboard connector on the driver board.
Replaced all the wiring harness solenoid connectors.
Replaced both transistors for solenoid #6 (Had previously been replaced, solder jobs looked awful). Used a TIP102 instead of TIP120
Replaced the 7408 for solenoids 1-4 and the socket, same reason as the transistors. Used a 74F08 chip instead of the normal 7408.
Replaced a fried coil at #6, which had the sleeve melted in it.
Tested all coil ohms, all check good.
Tested all coil diodes, all checked good, but since you have to half remove them to test them I just replaced them all. (got a roll of 100 diodes for $4).

Tested all the TIP120/TIP102's as well as the 2N4401's on the board with my DMM, This is where it gets odd. With the wiring connector for the solenoids removed, they all test OK individually. When I put the connector back on, I get 5v at the base but 3.5v at the emitter on all 8 of these..... but normal on 9-16.

If I disconnnect the connector for these 8 coils, none of the others have any issues and work normally.... even if there are only a couple of them. Once I connect 1-8, these 8 all lock-on and the breaker pops. (using a 3amp breaker until I get this diagnosed properly.)

I'm at a loss here what to look for next. I'm going to try using the logic probe feature on my DMM tomorrow, but that's new to me and I'm not sure what I'm going to be finding. Anything else to suggest? I may also throw a new 74F08 for the 1-4 block of solenoids, that way all of these have new chips for them, and with a socket there I can also unplug them 4 at a time too. After that, then what? The PIA chip maybe?

-Hans
 
I would try new EPROMs for grins. That would be the end of the shotgunning if it didn't work. At that point I would pull the MPU and go over it with a fine tooth comb and Leon's test ROM.
 
I do want to try a set of fresh rom's...... I just need to get hold of a burner somehow. I'll check with a couple of the tech's at work, they seem like the type to have one.

I'd also love to figure out how to read the ROM files for the game. There's a couple things that I find odd in the wiring diagrams that I would like to see if they are still programmed into the game like the rebound bumper switches are.

I still have a few things that I want to check while I'm at it. The filter caps on the driver board come to mind.

-Hans
 
huh.... I think I may have found it in a very unlikely place and almost totally by accident.

Bad fuse clip for one of the two logic circuit fuses on the circuit board. Wiggling the fuse around appears to make the problem go away. Either way the holder needs to be replaced, but I'm going to wait until the solenoid locking issue occurs a few more times to test if that really does cure it or if I'm getting a pinball placebo effect.

-Hans
 
Well, here's a happy update on this one.

I replaced the faulty fuse clip on the power supply, and after about 50+ games and vigorously testing the hell out of it by manually pressing playfield switches, it's looking really good. I have not had a single recurrence of the solenoid lockup issue. It also seems that the solenoids are sounding cleaner when they fire, more crisp and less "uncontrolled crashing" of a sound.

Man, I hope this solved it. I'm also happy that I got the bell running too, just needed the leafswitch flipped to the other side of the ringer arm. That makes all the solenoids and switches reliably working. Now I just have two controlled lamps to deal with, which I suspect to be bad sockets, and about a half dozen GI sockets too.

Ahhhh, it feels good.
 
Well, that Wasn't it after all. The good news is that I've also, I think, really found it this time.

It's been running flawless since replacing the 6821 PIA for the solenoids. I finally figured out the logic probe function of my DMM, and found that it was locking on and causing the solenoids to stick. I'm just glad that somewhere along the line the driver board already had sockets swapped in, saved me about an hour of work that I would have been nervous about.

-Hans
 
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