I'm having some problems diagnosing the following issue with a Black Knight that I'm working on. The game came to me with solenoids 1-8 completely burnt, and the left side Magna Save also burnt, and it's fuse blown. The game would lock on all 9 coils when powered. I was told this happened randomly while game was not being played, but in attract mode.

I sent the boards out for repair while I replaced all the burnt coils, ensuring correct diode polarity. Got the boards back, Solenoid PIA was replaced directly to the board, no socket. all 8 TIP 120s replaced, and that's about all I noted visually. I checked voltages coming from the PSU, and all check out. I reconnected everything except for the connector for sol 1-8 and left out the 10 amp fuse for the left Magnasave magnet. Game boots and all features check out in test. Plug in the connector and all solenoids check out. Game was play tested for a week, probably 3-4 hours worth. Replaced both Magna save magnets at this time, and checked function with new 10 amp fuse. Again, no issues. 5 games in, and I go to start game 6, and the game won't start from attract mode. I check the start button in test, and it works fine. I checked the ball trough switches and it appears that one isn't registering. I make a quick adjustment, and it registers. Go to start a game, and it fires up, but within 30 seconds, I see and smell smoke, and turn the game off. Can't tell which of the TIP 120's is smoking but turning the game on, and all 8 coils lock on again. Magna save doesn't blow 10 amp fuse though. Lots of smoke from the TIP 120's for Q21 and Q23 the two upper PF drop target banks.

Turned the game off and am sending the boards back for warranty repair.

Problem is I don't know if it's a board problem, or something causing the boards to fail in the same manner by a fault on the playfield. All coils are new, Magna Save coils from Marco with the varistor installed, and everything worked fine for a week. Only 5 games after installing the Magna save did this occur, but it was in between games, in attract mode. One game finished fine, the next didn't start, and it looked like a simple switch problem, until it started after the adjustment on a trough switch, completely unrelated to the coils in that string.

What should I be looking for at this point? What could cause this PIA to fail (my guess, considering that half of the coils are locked on) from the playfield? If it's failing on the board side, what keeps causing it to fail?

ALL help is appreciated as I'm stumped at this point.

Hi Schwaggs,

Noticed that smoke was coming out of the backbox after I was able to get the game to coin up and start a new game (after it wouldn't start) Thought at first it was just a flaky switch adjustment. So no, the game was started, and then transistor smoke. Then I could hear transistors lock on. Turned the game off, and right upon start up, they all lock on.

No, the 40 pin interconnect wasn't replaced.. and I questioned that. To be honest though, it appears that the female connectors are somewhat new (meaning that they aren't original, and I suspect they were that way when I sent the boards out, just dont recall making a specific note of it is all). The male pins however appear to be the originals.

I just can't see what intermittent fault could be on the playfield that would cause this failure to happen. .TWICE. I'd suspect the boards first, and while they're being repaired under warranty, I suspect there won't be a 3rd time that they'll do so. They've already mentioned that they did a burn in test and put it in their "test BK" for hours on burn in without incident. Well I burnt it in myself in dozens of games, and then all of a sudden between finishing one game, and trying to start another, I'm right where I started with half of the coils locked on and most likely a bad PIA.

If anyone has an idea of what to look for to determine if it's a board problem, vs a playfield problem that would help tremendously. No work was done to cause a short with the game on. No switch matrix shorted to lamp or solenoid problems (learned the hard way years ago) and even that usually takes out the lamps or switches, NOT the other way around...

Could the relay that runs the Magna save cause this kind of failure? Again, no fuse blew this time after the replacement magnet was installed, but these are the newer style enclosed relays, not the older coil run through the plastic frame and leaf switches they used on earlier games. Cant see how this would cause an issue other than overheat and blow a fuse though if it were locked on somehow.

Bump... No ideas anyone?