(Topic ID: 268936)

DMD cracked after getting too hot

By yaksplat

3 years ago


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  • Latest reply 3 years ago by yaksplat
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#1 3 years ago

Friend of mine just bought a Getaway and he told me that it was no longer booting up and the screen was garbled. I go over there and wiggle all of the cables, disconnecting and reconnecting them all. Turn the machine back on and the screen was still garbled. I noticed that led 2 was off on the driver board, but the rest were on. I started testing the voltages and then POP! the DMD glass cracked and it went off. Then i immediately disconnected it. The glass was too hot to keep your fingers on for more than a few seconds.

Voltages that i read: (from memory)
5v was reading in the low 4s
50v was 85

I don't have the machine here, but i brought the driver board with me to check some things out. Diodes in BR5 are reading 0.4 and the rest are reading .462. No open diodes in any of the bridges. LM323k was replaced with a PSU5

I'm going to hook this up to my whitewater transformer and get exact readings on the test points.

#2 3 years ago

I encountered this a while back:

https://pinside.com/pinball/forum/topic/has-anyone-seen-a-dmd-spontaneously-crack-the-glass

For voltages, keep in mind that circuits with no load will read a bit higher voltage than with a load connected.

#3 3 years ago

It sounds similar, but in this case there were no blown fuses.

Also, this was a new replacement DMD that was only a few months old.

What would cause LED 2 to not be on? I haven't been able to find any threads about that since it's such a generic term.
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#4 3 years ago

The DMD voltages are not generated on the driver board, but on the DMD controller board. Obviously there is somethin wrong with the DMD voltages.

#5 3 years ago

Ended up that there was a bad/cracked solder joint on C5. I replaced it and C11 as it looked like the same person did them both. The 5v power is back at a solid 5.1v with no load and all of the proper led's are back on. All of the voltages test out correctly on the board.

I also found that the fuse at F115 blew, but had welded itself back together producing a false positive. Works great under no load.

I've got him bringing me the DMD controller board so i can test that out as well and hopefully figure out what caused the DMD to blow.

#6 3 years ago

DMD controller tested out well and I installed it in my whitewater. Everything worked perfectly.

I'm starting to think the DMD in there had just self destructed.

#7 3 years ago

ForceFlow I have a theory as to what happened here. Not 100% sure, but this is the best that i can come up with as an explanation. The top third of the screen is where the garbled pixels were located.

I'm guessing like other electronics, plasma displays are actually strobing at some high frequency that we can't see. With the 5v failure in this machine, the garbled screen was not strobing, but in an always on state for certain nodes in the display. This created a great deal of heat that was not being dissipated. The top third of the glass was heating unevenly compared to the lower 2/3 and this caused a difference in expansion within the glass. That led to the crack.

Now that the 5v is fixed, this should no longer happen.

#8 3 years ago
Quoted from yaksplat:

forceflow I have a theory as to what happened here. Not 100% sure, but this is the best that i can come up with as an explanation. The top third of the screen is where the garbled pixels were located.
I'm guessing like other electronics, plasma displays are actually strobing at some high frequency that we can't see. With the 5v failure in this machine, the garbled screen was not strobing, but in an always on state for certain nodes in the display. This created a great deal of heat that was not being dissipated. The top third of the glass was heating unevenly compared to the lower 2/3 and this caused a difference in expansion within the glass. That led to the crack.
Now that the 5v is fixed, this should no longer happen.

Interesting idea.

After the display cracked on the game that I worked on, I rebuilt the DMD board--although since it's been so long, I don't exactly remember if I rebuilt it first before connecting a replacement display, or rebuilt it a few months later just to bulletproof it.

#9 3 years ago
Quoted from yaksplat:

forceflow I have a theory as to what happened here. Not 100% sure, but this is the best that i can come up with as an explanation. The top third of the screen is where the garbled pixels were located.
I'm guessing like other electronics, plasma displays are actually strobing at some high frequency that we can't see. With the 5v failure in this machine, the garbled screen was not strobing, but in an always on state for certain nodes in the display. This created a great deal of heat that was not being dissipated. The top third of the glass was heating unevenly compared to the lower 2/3 and this caused a difference in expansion within the glass. That led to the crack.
Now that the 5v is fixed, this should no longer happen.

Sounds plausible, but I don't think that's it. If the image was garbled, the display would still need to refresh at the normal horizontal frequency to generate the garbled dots. If you has a situation where the display was scanning normally and instead had some locked on rows causing a solid orange section, yeah that would generate more heat. Did the garbled section look any brighter than the non garbled part? I see a similar artifact when turning a game off, usually there will be a few dots that are really bright for a split second before the DMD goes dark.

#10 3 years ago

All of the garbled dots were solid on. There was no refresh occurring.

#11 3 years ago

In that case then yeah, the rows were locked on at 100% duty cycle which probably caused excessive heat.

3 weeks later
#12 3 years ago

Hooked it all back up with the fixed 5V in the driver board, the existing DMD controller and a new DMD. Everything worked perfectly. I pulled the 5V daughterboard from the machine which was no longer needed since i fixed that issue.

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