(Topic ID: 252954)

TZ Ground short


By Scosti

11 days ago



Topic Stats

  • 28 posts
  • 6 Pinsiders participating
  • Latest reply 7 days ago by Coyote
  • Topic is favorited by 2 Pinsiders

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#1 11 days ago

So was switching bulbs on my TZ and must have blown something...

Getting a "Ground short Row 1 is stuck closed"

When running test it says the same for rows 3,4,5 and 7 as well and ball popper opto stuck and clock broken.

I’ve then Disconnected some switch connectors from the CPU.

When J206 and J208 are taken off cpu board all “ground shorts” are gone. When I run test, it now only says clock broken and ball popper opto stuck.

Take off J212 and J205 (J206 and J208 are still off) get a Error of “replace fuse F115 and F114”

Looking at Replacing the U20 and U14— from. What I’ve read.

Had been working 100% before , so I’m guessing I shorted out something. When I changed the bulbs.

Any ideas or help? Am I on the right track?

Thanks

#2 11 days ago
Quoted from Scosti:

so I’m guessing I shorted out something. When I changed the bulbs.

With power on no doubt, which shorting a single lamp socket to a switch, which both are different voltages. Always suggested to change bulbs under the playfield with power off.

#3 11 days ago

Test F115 and F114 with a meter.

#4 11 days ago

So would it be fuse issue.. the U20 and U14? Or all of those? And would replacing those fix it? Or more potential board issues?

Yes- note to self. Turn off power when switching bulbs.

#5 11 days ago

If not a fuse, I'd go with this.

LTG : )

#6 11 days ago
Quoted from Scosti:

So would it be fuse issue.

Starting point is always a fuse. Without power, nothing happens. But it still blows, yeah, likely U20.

#7 11 days ago

So the fuse will blow when the machines off. And if it does it’s the U20?

#8 11 days ago
Quoted from Scosti:

Take off J212 and J205 (J206 and J208 are still off) get a Error of “replace fuse F115 and F114”

This happens when you remove the connector to the coin door interface board. This is where switch #24 is located. When the game can't see switch #24 as closed it assumes that there is something wrong with the +12VR. This should disappear when you reconnect J212.

#9 10 days ago
Quoted from Scosti:

When J206 and J208 are taken off cpu board all “ground shorts” are gone. When I run test, it now only says clock broken and ball popper opto stuck.

Wouldn't this indicate that the issue is **NOT** on the MPU, so replacing fuses and ICs not help in this case?

Unless I'm misunderstanding what @op is saying, I guess...

#10 10 days ago

My ground row short went away when I replaced u20 and it was socketed to make things easier.

#11 10 days ago

If you take the plugs off and the short goes away I do think it’s on the playfield. Maybe make sure nothing has been moved causing a short. Inspect the area for anything touching that’s not suppose to.

#12 10 days ago
Quoted from Coyote:

Wouldn't this indicate that the issue is **NOT** on the MPU, so replacing fuses and ICs not help in this case?

That’s what I’m trying to figure out. When the J206 and J208 are off and no shorts are showing... it’s something under pf?

#13 10 days ago

Once the U20 is fried , should it still say “ground short” when the J206 and J208 are off... meaning it’s an MPU issue?

#14 10 days ago

In my past experience, yes - since the chip is fried and likely has gates shorted to ground. BUT - I am NOT an expert on that chip..

#15 10 days ago

Consider disconnecting A-16807 - the "Custom Opto SW10 PCB Assembly". Reconnect your CPU connectors (J206 and J208) and disconnect J5 on A-16807. This will isolate the opto board. If the source of the ground short is on the board it should disappear.

#16 9 days ago
Quoted from DumbAss:

Consider disconnecting A-16807

Disconnected J205 kept the J206 and J208 on and still says “ground 1 short stuck close”

So opto board is clear of being the source for the ground short?

Thanks everyone for their help so far! I really appreciate all of it!!!

#17 9 days ago

Here’s a pic of the U20 IC— looked fried?FullSizeRender.jpg

pasted_image (resized).jpeg
#18 9 days ago
Quoted from Scosti:

Disconnected J205 kept the J206 and J208 on and still says “ground 1 short stuck close”

Disconnecting J205 won't change the situation. Those are a bunch of orange wires that are direct grounded switches - not part of the matrix. You need to disconnect J5 on A-16807 - NOT J205 on the CPU board. This will isolate the A-16807 board from the switch matrix. If the source of the ground short is from the A-16807 board then it should disappear. J5 is a bunch of mostly white wires, some green wires, a black wire and a gray wire.

Quoted from Scosti:

So opto board is clear of being the source for the ground short?

No. See the above. Disconnect J5 on A-16807 while leaving all the other connectors on the CPU board connected.

#19 9 days ago
Quoted from DumbAss:

A-16807 board then it should disappear

BINGO! Took off the J5... just get “ball popper opto stuck”. No more ground short.

So from what I gather your telling me is the issue is on the A-16807.?

Thanks for the help

#20 9 days ago
Quoted from Scosti:

BINGO! Took off the J5... just get “ball popper opto stuck”. No more ground short.
So from what I gather your telling me is the issue is on the A-16807.?

Yes. I'm overly cautious and I usually like to be 100% sure before proceeding. If I were doing this diagnosis I would disconnect J5 and see the problem disappear. Reconnect J5 and see the problem re-appear. Disconnect J5 again and see the problem disappear. Doing nothing else to the machine and seeing that kind of result leads me to conclude the problem is on the A-16807 board. That's a custom 10-opto switch board. You CANNOT replace it with a generic 10-opto switch board from another machine. This one for TZ was only used in TZ.

If you're comfortable with PCB diagnostic and repair I would bet that one (or more) of the LM339 ICs on the board is bad. You can purchase one @ https://www.pinballlife.com/10-opto-replacement-board-for-twilight-zone-a-16807.html if you just want to replace the board with a new one.

The old board can be repaired. I would not throw it out. If you decide you want to throw it I'd be interested in it.

#21 9 days ago
Quoted from DumbAss:

I would bet that one (or more) of the LM339 ICs on the board is bad.

So I’m gonna get me some LM339s. There all socketed so should be an easy swap... and we will see how that goes...

Thanks

#22 9 days ago
Quoted from Scosti:

There all socketed so should be an easy swap... and we will see how that goes...

The ICs were NOT socketed from the factory so someone has done some work on that board. Check the previous work to make sure that the circuitry (continuity) is correct.

#23 8 days ago
Quoted from DumbAss:I would bet that one (or more) of the LM339 ICs on the board is bad.

YOU THE MAN!!!! Swapped all 3 of the LM339 out and all is 100%!!!!!

Thanks so much everyone!!!!!

#24 8 days ago

This is a good reason for turning off the game when changing anything on the underside of the playfield, including changing the #44/47 bulbs. It is a very small risk replacing #555 bulbs, but still if you have a tool in your hand, turn the game off.

#25 8 days ago
Quoted from PinballManiac40:

if you have a tool in your hand,

Words of wisdom. You should never have your tool in your hand, when working on a pinball machine.

LTG : )

#26 7 days ago
Quoted from LTG:

Words of wisdom. You should never have your tool in your hand, when working on a pinball machine.
LTG : )

... What about someone else's?

#28 7 days ago
Quoted from LTG:

TMI
LTG : )

Hey now, you started it. I was just takin' it to the next level. Sheesh.

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