I am having an issue with Row 4 in the switch matrix on Twilight Zone
I am still collecting facts and I will post here as I try to work thru this.

If I do not use the game for several days I get an error.
The game will boot ok. (Using 9.4CH Eprom)
You know there is going to be an issue if it prompts you to go into reports.
If it doesn't give you the prompt, all is fine.

If you leave it in attract it is fine.
If you go to start a game it spits out a ball then gives the (2) Danger warnings and goes into tilt.
Sometimes if you plunge the ball it will shoot it back to the out hole and give a second ball ( and tilt that one also) and other times it will not.
The error is always "the clock is broken".

If I use the game everyday. There is no issue.

If you go into test (again, please keep in mind I am still gathering facts)
(14) Plumb bob is closed
(24) Always closed is blinking ( open/closed)
(94) 30 second is blinking.

You will hear the gumball VUK (74) shooting with nothing in it.
And in some cases LH flipper F4 will blink.

Usually, within 8 to 10 minutes of searching the tests, it will correct itself and all is well. There is no clock error and it functions fine. There is no tilt and it is fine. You can boot, reboot, and play a game(s) normally.

Tonight the game again had the row 4 issue.

Switch 24 "always closed "pulses between open and closed. It is not consistent. The resulting tone is two pulses, three pulses, five, 20 etc then back to 2, 3.
IF I disconnect J1 on the coin interface door, switch 24 closes.

Unplugging J212 at CPU made no difference.
Unplugging LH flipper opto made no difference

To override the issue tonight, I started a game (TILT), plunged the ball. It was returned, (TILT) and it was returned a 3rd time and I was good to go. Credit dot disappeared, game played fine and clock worked as it should.
Reboot: fine and played a game.

I am wondering if D2 on the coin door interface board is bad. Can a diode be "weak" ?
Not sure what else it could be since it can correct itself.

Yes, disconnecting J1 did make switch 24 close in test. Removing any of the other plugs on that board had no affect on SW 24. It stayed blinking.

It doesn't make sense on many levels. The fact that it will go away is frustrating.
Sw 24 blinks open and closed like it is connected to an attract circuit.
Because it makes a tone for open/closed you can count the pulses.

I will have to wait to have it error again.
It is playing fine and the clock is working fine.
I can boot and reboot for the rest of tonight and there will be no errors, no credit dot.

I will try it again tomorrow after work.
If it errors I will look for more clues.
I will also remove an inspect the CDI board and change D2 to rule it out.

The cpu looks good and has a remote battery holder.
I will post some clear photos tonight.

Is it possible the problem could be the eprom?
I changed this about 150 plays ago.

I chased a booting issue on my DEJP only to find out the NVRAM failed after 200 games.

The CPU

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938707E5-5203-4403-9FC7-922BE35B6E30 (resized).jpeg

Thanks
Will do.

The episode last night was very short. (Likely because I have been turning machine on each night)

SW 24 WAS open.
In test the switch was open but not toggling between open and closed.
I reached for JI on CDI and switch 24 closed.

Not sure I actually touched the plug before the switch closed but I removed and inspected the CDI.

I reflowed the headers for J1 and J6. There was no obvious cracking or deterioration.
I changed diodes 2 and 3.
I also changed the plug on J1.

I will try it again tonight.
I will be away for weekend so Monday evening will be the best opportunity to do testing.

Had an extended episode tonight.
Clock was disabled last week. The clock did not fault but the machine still tilted.

In test sw 24 blinking open and closed. There is a pattern to the beep/ blink. I videoed it with my phone but i am unable to attach it.

Disconnect J1 on CDI and sw 24 is open. ( i was likely wrong in my previous post)

Disconnect J212 sw 24 will close occaisionally but mostly open. (It will blink closed sometimes)

Disconnect J206, Sw 14 and 24 close.
Remove both plugs 14 closed and 24 open

Closing plumb bob switch when this is happening, with all plugs connected does not close 14.

Tonight i went thru each switch in row 4 with the machine having switch 24 in open / closed blink mode. When i got to the powerfield entry switch , switch 24 closed.
Not sure if activating switch made a difference or if enough time had passed for episode to pass.

Still chasing this.
I did cure the gumball machine coil popping when game is in this sw 24 open /closed state.

It was popping the coil and sw 74 read open.
I blocked the opto in sw test and it made no difference to the switch or the popping.
Of course this condition disappears when sw 24 finally closes.

I changed opto 74 and at least this issue has dissappeared for now.
Since the center lock is on this row as well, i am going to change it as well.
I am also going to change D6 on the mpu.
Then, wait a couple of days......

I have a video of the sw 24 test but cant figure out how to attach it

I am going to send my cpu and power board to a local board guy.
I believe the issue is U18 a LM339. Chance Tess at pinfest agrees with me.

My board specialist sides with Pin_Guy saying he believes it is the 12volt circuit.
I measured 11.90 vdc at all times at TP 3. During episodes and afterwards when it was running fine that voltage was always the same.

If it is in the 12v I would guess it is a failing capacitor in that line. The symptons do mimic failing capacitors i have seen in the past.

I will report back what this turned out to be. If it were not a TZ with Williams tiny fragile traces, i would change all the caps in that line. If that didnt work i would change U18.
I have board experience but i do not have a capable solder removal system/tool that could guarantee board survival.

Update: my boards are coming back.
I was told that the power supply was upgraded and the processor chip had one bent leg and needed a new socket.
I never touched the processor in the 8 months i have owned the game and the sw 24 issue has been more recent. (Since june)

He also said he never saw switch 24 open.
If the boards check out ok in the tester, my issue is likely in the machine.

I am not confident that the problem is solved.
From here , i will likely buy a different clock board ( a common denominator) and continue changing the optos in that row.

I will report back when the boards are back in the game.

I am certainly no expert. And i apologize for my limited knowledge on this.

But if the boards check out ok, and the problem persists, then it must be in the machine.
Row 4 is always the issue.

Switches 14, 24, 94, sometimes F4 register contrary to what they should when an episode happens. Up until i changed the opto on 74, it too was an issue.
The clock always comes up as broken during an episode. A credit dot is registered for the clock.
Switch 24 pulses open/closed with beeping/pulsing some pattern.

If you start a game, machine immediately tilts and stays that way until the episode passes. From 1 minute to 10 minutes. It is like something has to warm up. The machine must be off for several days in order for issue to appear. You have one shot at it and once it passes, it will have to be off for more than 2 days for issue to reappear. Once cleared you can reboot over and over with no problems. You can wait an hour and reboot and it will be fine.

Once the episode passes, the credit dot disappears.

The left flipper has new optos.
74 has new optos.
I will be changing the remainder of the optos in that row.
After that i will disconnect each switch in that row to see if problem goes away.
A new clock board of a different brand will rule out that opto.
From there I will trace the entire row/ column wire loop to look for something pinched or touching.

I agree. See post 16.
I should have the boards back tomorrow or wednesday to try them out.
When the board guy had them in the test fixture they behaved ok. I told him specifically what to look for and how it occurs but i was not there when he did the work.
I will wait to try them out.
Finding another board to swap in will not be easy.
Thank you for your input. I greatly appreciate it.

Put boards back in.
Powered it up, credit dot. Clock is broken, start game, tilt.
Switch test: sw 24 open/closed pulsing.

U20 got changed on mpu.
Looks like a solid state regulator was installed on driver.

I am stiil where i was before.
Walked away.
It will be up to me to figure this one out but not tonight. It is 95*F in my garage.

I have checked each of the capacitors, resistors and diodes for row 4 on the mpu. Each one tests out ok and the readings are the same for unrelated but similar components on the mpu.

Yesterday, i completely disconnected sw's 14, 44, 54, 74, 84, and 94.
It still had the tilt issue at the start of a game.
Sw 24 still blinked open / closed.
Sw 14 also blinked open/ closed.
The gumall vuk kicks 5 or 6 times.
Lock kicks 5 or 6 times.

The game always shows a score of 2 million points when the episode is over.

I plan on doing several more tests to try to pin this down.

I booted the game with plug 208 disconnected.
It did recognized there was a 12v issue.
When i started a game with plug 208 disconnected, it tilted. As usual.

The gumball and lock kick when the switches are connected as well.

With J208 and J212 disconnected, the clock comes up broken as usual but without CDI there are no closed switches.

Plugging 212 back in first showed all switches as they should be.
Plugging 208 back in allowed me to start a game without a tilt.

Either my time ran out and it corrected itself or made a difference. Tomorrow i will start it up with both disconnected the first time

All is well. Played a couple of games. Clock works fine, credit dot clears . I am fine until tomorrow.

My game is currently booting up and starting a game without tilting. I do not believe it is fixed but time will tell. I went away this weekend and the machine booted up without errors and started a game without tilting today when i returned.

I plugged and unplugged and booted the game. Different combinations.
Eventually narrowed problem down to J212.

It made some sense that the issue was in that circuit. The tilt and power source for sw 24 come from cdi. J212 is the mpu connection to cdi.

My board guy found no issues with the driver or mpu. I trust him. If it were there, i think he would have found it.

I had already replaced the connector at the cdi end.
I followed the yellow /white wire from that plug to the mpu. There was no trauma to the wire.

I pulled J212 from the board and the header looked fine.
I pulled the pin out of the connector and crimped it to ride more tightly on the header. Put it all back together and it has been starting up ever since.

Time will tell......

Didnt quite make it a week.