(Topic ID: 323191)

Display board shorted, now what? SOLVED

By Iamcommando

55 days ago



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  • 9 posts
  • 4 Pinsiders participating
  • Latest reply 39 days ago by Iamcommando
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#1 55 days ago

I think I shorted out my Earthshaker display board while performing a repair. Most of the segments on most of the digits are out on both top and bottom glass. Looks kind of like the right most digit is 'burning-in' many updates as all segments are always on. Prior to my 'repair' everything worked reasonably well. No burned spots on any of the boards, and no fuses blown.
Voltages look okay. Picture shown during attract mode.

I've started looking at the pinwiki page for displays, and browsing the web to get ideas where to start. I'm going to check the 39k resistors and other power components, but what is a likely component on the display board itself? Not much on there but resistors, buffer chips, and expensive obsolete driver chips.

I'm a noob to pinball repair, but feel confident in my repair and troubleshooting skills in general. Any help on the most likely culprits would be much appreciated!

Many thanks!
Bob

Screenshot_20221001-150341 (resized).png

#2 55 days ago
Quoted from Iamcommando:

I think I shorted out my Earthshaker display board while performing a repair. Most of the segments on most of the digits are out on both top and bottom glass. Looks kind of like the right most digit is 'burning-in' many updates as all segments are always on. Prior to my 'repair' everything worked reasonably well. No burned spots on any of the boards, and no fuses blown.
Voltages look okay. Picture shown during attract mode.
I've started looking at the pinwiki page for displays, and browsing the web to get ideas where to start. I'm going to check the 39k resistors and other power components, but what is a likely component on the display board itself? Not much on there but resistors, buffer chips, and expensive obsolete driver chips.
I'm a noob to pinball repair, but feel confident in my repair and troubleshooting skills in general. Any help on the most likely culprits would be much appreciated!
Many thanks!
Bob
[quoted image]

I'm even more a newbie than you are, but just looking at the symptoms, it seems like you've somehow disabled a refresh/sync signal that would otherwise cause display signals to be toggled between different alphanumeric elements, i.e. all the displayed data is getting sent to the same element. So if you've got a schematic that shows you the functional units of the display inputs, I'd say that'd be a good place to start.

Of course, if you have a way to verify that the fault is in fact in the display board instead of a control board, that'd be an excellent starting point too. But you probably already knew that.

#3 55 days ago

Pete_d,
That makes sense to me. From what I can tell from the schematics, looks like there's a series of nor gates that are used to select which digit is being strobed. Since those are cheap, I'm going to try replacing one and see if there's a change.

I was able to get it into diagnostic mode and the right most digits in both the top and bottom displays appear to be mostly functional. As the digits cycle from left to right one at a time, most of the top digits are faint, if at all, but the bottom digits are all fairly bright. But when the segments cycle though one at a time, a few random segments light across the top and bottom digits, but not many. In both the digit cycle and the segment cycle, the right most digits on top and bottom seemed to work mostly fine.

But also of note, the right most digits are lit as the digits test cycles, even when other digits should be lit.

Thanks again for the help!

Bob

#4 53 days ago

I recently picked up a earthshaker, the display had a few missing segments but it didn’t matter I wanted to change it to a LED display. I was thinking blue but decided to stay with the original color. To fix the original I just had to re-solder a few pins that broke from a previous solder job. I ended up selling it. It almost fully paid for my LED display. Good luck with your earthshaker.

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#5 53 days ago

Already reseated the display ribbon cable on both ends? Power off doing this, BTW.

#6 49 days ago

PinballManiac40,
Yeah, tried all the normal things. Reseating the connectors, inspected the board for burn marks, shorts or cold solder joints. Since the right most digits on upper and lower displays are okay, makes me think it has something to with the strobe signal to control which digit is lit. Any other ideas?

Thanks, Bob

1 week later
#7 40 days ago

Ok, figured it out. It was the 4049 quad nor gates.

I tried my logic probe up-stream at the PIA and other components and got a pulse signal at the output pins as expected. I moved on to display controller board. I figured it was not the hex buffers which control the segments since I observed most of the segments working on both the top and bottom plasma displays during the display diagnostic test. When I probed the nor gates that control the strobe signals for each digit however, I still seem to be getting something at the outputs. Strange.

I decided to try and remove, socket, and replace the nor gates in different positions, to see if the always working digit moved from the right-most digit to another position. Bingo. I used my hot-air solder gun and it took only a few minutes per chip to remove, solder suck out the holes, clean up with solder wick, and place sockets in all the logic chips (4049s and 4001s). I ordered replacements from Jameco for less than a dollar per chip and display worked again! Mostly...

I had a few segments out on the bottom display and upon inspection discovered that my roughhousing of the display leads to get to the chips had broken off one lead flush, and caused two others to detach from the glass. Bummer.
Broken leads

For the lead that broke flush, I applied some solder paste to blob some solder on, and gently attached a fine wire. That fixed one segment.
solder blob on flush broken lead

The other two were harder because the actually detached from in-between the glass sandwich. I made a wire lollipop and applied more paste to the terminal and the lollipop hoping I could wedge the lollipop up against the terminals. It worked, and I have all my segments back!
Fixed detached leads with lollipops made with a tight wire spiral at the terminal end

Since I'm convinced the whole problem happened because I shorted out the logic elements while doing another repair, I placed a paperboard insulator on the back of the display. Overkill for sure, but I don't want to ever do that again!

Thanks for the help and suggestions!

Bob

#8 39 days ago

That's awesome. I'm especially impressed you were able to repair the broken leads to the display. That's some finicky work to be sure. Here's hoping the new connections remain reliable!

#9 39 days ago

Thanks. For sure won't last forever. Luckily they are the 'dot' and the 'upper left X' segments, so nothing too critical. Just happy to have it all back together!

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