(Topic ID: 20238)

Fixing a dead DMD column or row - Cherry 4205 DMD

By tta583

8 years ago

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  • 8 posts
  • 5 Pinsiders participating
  • Latest reply 1 year ago by kbliznick
  • Topic is favorited by 11 Pinsiders


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#1 8 years ago

I have been a video guy for several years but have, finally, started to wander into pins. Everyone said it would happen...but I digress. I have acquired a few recently. All needing work to some degree. The first one I have actually started to work on is an Addams Family. One of its issues was a dead column in the DMD. Below is a copy and paste of a thread I posted on the Pin forum over at KLOV. Pinside being pinball oriented I though it may find some use here as well.

Something I thought I would share in hopes it helps someone else. In working on my Addams Family I realized I had a dead column in the display. Looking around online I have seen where folks had fixed dead rows or columns on various Dot Matrix Displays. The most common "How To" to find seem to be of a type that uses a wide ribbon cable to the glass from the board. Not sure of the brand. Over time the wire from the ribbon cable breaks at the glass and you end up with a dead line. The solution is to Dremel out the glass, expose the wire, and in some form or fashion, remake the connection.

In my situation I have a Cherry DMD with a PN of 0001-4205-B on it. Actually, I have 2 at hand. One, the one with a dead column, is in an Addams Family. The second is in a High Speed 2, Getaway. These DMDs have a pin that comes from the board that then flattens out and take a 90 degree bend that is then sandwiched between the 2 layers of glass which makes up the display. Looking through the front of the display you can see where another "contact", the lead to the actual row/column, laps across this pin. I am not sure how they are connected other than via applied pressure from the 2 layers of bonded glass.

Here is what you will need for the fix:
-Soldering iron.
-Short piece of 20 or so gauge wire.
-Dremel or some other rotary tool with a small diameter diamond chip coated bit.
-Alcohol and some Q-Tips.
-Conductive paint like from a window defogger repair kit.
-Small paint brush.
-Masking tape.
-Hot glue gun.

Nice to have:
A magnifying glass or visor.
Some dental picks.

#2 8 years ago

First I verified the game was good by swapping in the display from the Getaway. All was good. As an alternative, if you do not have another display, you can let the full display test run to see if the game kicks back anything it thinks is wrong.

Next I started looking at the DMD. I checked continuity from the resister behind the dead line through the front of the board then up to the glass. I also gave the pin a little tug with a dental pick to see if it was broken at the glass. While I had the meter out I checked the resistor by comparing it with its neighbors as well as continuity from the inside of the resistor back to the first IC. Everything checked out so I was back to the “classic” problem of a break going to the line at/in the display.

I took a Demel with small diameter diamond chip bit and started to work into the glass hoping to get to the contact that ran back into the display. A little alcohol on a Q-Tip cleans the glass dust nicely. As best I can tell that contact is a foil or some very thin material. The pin that came from the board eventually slid out. It was apparent it had some heft to it. I just desoldered it and removed it all together. The contact leading into the display seemed to vaporize at the slightest touch. I even attempted to get close then chip out the remaining glass with a dental pick. No luck. What I did notice was a little nub at the back of the pocket I cut out. That turned out to be my ticket.

I ran to the auto parts store and picked up a window defogger repair kit. I wanted to use the conductive paint from the kit to make my connection.

I grabbed a piece of 20g stranded wire (solid would work), stripped off a couple of inches, twisted it, then soldered it into the PCB. I cut it off long enough to be able to bend a little goose neck in it that would sit up on the glass. Before I bent it I tinned a little solder on the end to keep the strands from splitting. I bent then end so that it would sit on the lower piece of glass with some downward pressure, then I slid it off the edge.

Now comes the conductive paint to make the connection. Using the dental picks and a magnifier I taped the edged of my cut. In my case I could see the edges of the neighboring pins. I also noticed that when I cleaned the cut with alcohol I could see some wick left and right between the pieces of glass. The idea was to keep the paint in the channel and out of the other pins. Using a very fine detail brush I applied the paint down the channel making sure to get to the very back so that I could cover the little exposed nub of a trace. I also coated the wire lead I soldered in earlier. Now I popped the wire lead back up onto the glass. The paint from the kit I bought seemed to tack pretty quick. I re-coated twice in the next minute making sure to heavily coat the wire to glass point of contact. Once I was happy I pulled the tape off and let it dry for a couple of hours. After it dried I took a dental pick and scraped the sides of the channel to make sure no paint made it over to a neighboring pin.

I put it back in the pin and BINGO...no dead column!

Overall I feel the effort was worth it. I saved myself the cost of a new DMD. Granted, it took a little time but having done it once I can do another much faster so it was a good learning experience / experiment as I see it.

#3 8 years ago

Now a few pictures. I did not think to snap any as I worked so all I have it the almost finished product. Once I had it working I filled the cut channel with hot glue (Not Pictured) to seal it up.

Here is a view looking down on the display as it sits on my bench. You can see here how the pins from the board enters the glass "sandwich" and how the traces that run to a given line overlaps them. You also see how deep I cut the channel in the top layer of glass. If I had to do it again I would not have to cut as deep. I was attempting to expose the trace that ran back into the display. Much farther and I bet the display would have been a total loss. As I mentioned above trying to get a piece of the trace large enough to work with proved difficult so I turned to the conductive paint.

Top.jpg // Error: Image 35173 not found //

#4 8 years ago

Here is a pic that is a bit more edge on. I had to use the Macro setting on the camera...trust me, its a small space! If you try it invest in a magnifying visor. They are not that expensive.


#5 8 years ago

Nice article. Thanks for sharing.

3 years later
#6 4 years ago

Thanks for posting this -- it really helped!


3 years later
#7 1 year ago

Thanks, because of you I was able to repair a row in my DMD.

You don't want to drill right on the edge because the two pieces of glass are glued together there.
If you drill just a little further from the edge, you will find a gap between the two pieces of glass
which gives you access to the contacts.

My hole was small and the half of the contact closer to the dots was still under the glass.
That turned out to be an advantage. I put some solder on the new wire then
I inserted that end of the wire between the two pieces of glass along the length of the contact.
I applied some heat on the wire and the solder melted underneath the glass making the bond.

Like tta583 says, it's easier if you solder one end of the wire to the board first
and finish with the other end under the glass.

Be careful with the adjacent connections when drilling. I had to repair two rows instead of one
after breaking the pin next to the one I was repairing.

#8 1 year ago

Silver epoxy is your friend here on the DMD's with metal pins,

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