Just so I'm clear here. You can activate the Right flippers indefinitely and the game works fine. If you activate the Left Flippers the game will lock up in 3 or so flips? I'm assuming you're in test mode as well?

Have all the header pins on the driver, cpu and power supply board been replaced or at least had the solder reflowed?

Looks good for the cpu and driver board. What about the power supply board header pins? The same cold solder joints commonly occur on the power supply board.

Ok, so 1st, lets remove game play from the equation. I'm looking to see if activation of either flipper (on it's own) will reset the game. So, no balls in play. She/you can start a game but don't plunge the ball into the playfield. Just activate the flippers.

On the note of intermittent flippers:
The upper/lower flippers are on 2 different switches stacked on top of each other mounted on the side of the cabinet. If you slowly push in a flipper button you should be able to get the lower flipper to activate without the upper. These flipper switches pull full voltage/current so they will pit/burn out over time and either need replaced or resurfaced. Or, she simply didn't push the flipper button in far enough. If the former:

With the game turned off you can slip some 120 or higher grit sandpaper (nail file will work too) in between the contacts. Gently press the contacts together (from inside the cab) and move the sandpaper back and forth a few times. Do this to both contacts. If the contacts are pitted this should help with intermittent activation in the short run.
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So the issue here is being sure... your wife was playing a game at the time so something else may have happened when she thought she was hitting the right flipper only.

The key to successfully troubleshooting is taking a single sample at a time. If we mix up multiple things all at once then we don't have real information and we just circle the drain.

I'm trying to determine if only one flipper circuit causes the issue. It sounds like the left does it all the time on its own. I'd like to know for sure if the right does to, and if so how often. That's useful data.

So the flippers don't appear to be the cause from my POV. Can you describe the crash symptoms? Does it freeze, do the lights go out, displays top?? That kind of stuff. Or does it reset?

I'm interested in the fact that you couldn't start a game after it crashed. Did you check/test the start and trough switches to see if they were operating? It's been a few years since I owned a BK so I'm running on failing memories about the requirements to start a game on Sys7.

Does it work again if you leave it for a few hours?

To continue Schwaggs questions... how do the Power supply connectors look? Burned?

If it's crashed it's not going to react to any switches properly.

Requirement to start game on BK is the game has to see all 3 balls somewhere, upper lock, trough, shooter lane. Some of the games won't start if they see MORE than the 3 it's expecting, I forget if BK is one of those, but it def. needs to see at least 3.

The core issue is likely more than one thing causing the same results. I'd go ahead and replace the left flippers' diodes again with new ones anyway and make sure the band is correct based on the games' wiring to the coils (not necessarily the coil itself, since it seems strange that it became really consistent with resetting on the left flipper after that replacement....)

Maybe get another power supply as well, and not a RD one. They're relatively cheap and would rule that out as an issue.

For replacement power supply, you may want to try Kohout's boards:

http://pinballpcb.com/products/williams-system-7-11b-power-supply/

You'll have to determine which version you need though. Whether the main transformer is in the backbox or if it's in the cabinet should help determine which power supply you'll need to order from them.

Well in the classic sense of the term yes, but I didn't have a definition from him at that time as to the actual state of the machine and simply stuck with the terminology he was using.

It would appear that the game is still executing code (thus not actually crashed). The blinking lights and display are that of the game you were currently playing? Or did it return to an attract mode type of lights/score display scheme?

So it doesn't work at all now? That's easier to debug than intermittent issues. So when you turn it on is it running attract mode and it's not starting a game when you press start? Put it into test mode and see if it's registering the start switch and that it sees 3 balls as slochar mentioned.

Silly question, but is the game set to free play? If it isn't, are the coin switches working? Game won't start without credits (or set to free play).

Which switches are the balls activating in switch test? List the numbers that come up.

Do all the coils fire properly in coil test?

I was kinda thinking the same thing--if the memory got scrambled when it locked up, it might have removed the free play setting from the settings. Did the game ever boot to audit mode recently? When the game boots to audit mode, only the general illumination lights come on and some numbers appear on the displays. When that happens, you have to open the door and flip the power on/off/on to get to attract mode. If it did that, it's very possible the free play setting got erased/reset.

It's easy to miss things when you're moving quickly and concentrating on a different symptom. It would seem logical that the game could have booted into audit mode but you classified it as a crash (you weren't expecting audit mode) and power cycled again. Which would have cleared and moved you into Attract mode. Thus, it seemed like a crash and a reboot to recover.

I'd like to see us work through the game starting issue before we work back to the "crash" issue. Trying to solve multiple problems at once is going to get confusing quickly.

Post pics of both left flipper assemblies under the playfield. Maybe there's something funky with the wiring or a possible intermittent short someone might be able to spot from some pics...

Put a business card (or card stock/etc) in between the contacts of the cabinet flipper switches, one flipper at a time, and see if the game resets on only one of the flippers or both.

The EOS switch on the lower playfield flipper in your pic looks wrong. Can you get a better shot of that?

Yea, that's ok... to me it looked like someone used a newer style switch in that mech.

Ok, so it only fails when BOTH Upper/Lower flippers on the Left are activated at the same time. Seems like a load issue but it's odd that it's not happening with the right. (I'm still not clear on this even after reading the thread again) I wonder if one of the flipper coils has some shorted windings and is loading down the PS. Do you have a multimeter to test the coil resistance?

When is the new power supply arriving?

Lift a leg of the diode on each flipper coil, check for a bad diode.

I'm kinda hung up on the flippers causing this ATM.. Have you ever measured the resistance of the 2 windings of each of the flipper coils and compared them to known good coils?

I know it's a PITA to unsolder coils to do this.. Here's the flipper schematics, you might be able to unplug certain connectors and isolate them without removing them but you'd still need to slip a business card in the EOS switch to remove it from the resistance test of the hold winding.

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Post a photo of the boards cpu driver power supply.

Suspect a faulty internally shorted Left Flipper coil.

Sounds like he's looking for pics of the mpu (top left), driver board (bottom left board, connected to mpu via big 40 pin connector), and power supply board (top right)

try isolating the left flipper coils, so both aren't energising at the same time.

as the coils are activated by pressing the flipper button which closes both switches in the cabinet, put a piece of cardboard or paper between either and see what happens.

i'm curious to know if taking one out of the circuit then stops the issue happening?

have you checked the dual stack switches in the cabinet, that the solder tabs are all clear of one another?

From another thread with similar issue on system 7 repinning the power input on the mpu fixed it. Upper left corner of your mpu board.... Yours looks to be idc. Worth a shot.

just looking at the last pic you posted, and it may not be relay, but the plastic housing looks to be melted?

possible issue with the flipper relay?

In post #30, I can't really tell for sure, but the end of stroke switch looks like the soldered wires might have a rouge bit of wire that could be doing an intermittent short. Take a closer look and let us know.

These are supposed to be series coils, thus I'd expect one of the readings to be the sum of the 2 other. Yea I get that there's going to be some variation but upper right went down?

Are the winding wires securely soldered to the lugs?

you have lots of LEDs on your new power supply
have you tried watching these LEDs while you flip away to see if any of the LEDs flicker or dim?
might help to narrow it down?

I'm just now reading this and it's been 19 days since the last post, possibly due to the holidays. If you still have an issue, let us know and I'll toss in some ideas if I can. I've got 35 years of electronics under my belt (and 53 years of chub above my belt ), maybe I can pull a rabbit out of the hat.