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Thread: New toy, but it needs daunting amount of repair (LED screen)

  1. #1
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    Default New toy, but it needs daunting amount of repair (LED screen)

    Picked up a LED video screen in a horrible facebook deal. Long story I will tell at SELEM or something.

    Anyways, the panels were left in flight cases outside for 4 months due to a landlord dispute. At first things seemed ooookay other than the mildew smell and some rust on some things (Specifically certain screws and parts.)

    Turns out I guess the moisture penetrates the SMD LEDs and damages the junctions. This may lead to it causing issues in illuminating all the time when the array is scanned? So I get a bunch of sets of 4/5 LEDs that stay on.

    I have 24 panels, each 30" x 42" (large!!). Each is made up of 8 modules with 40 x 40 LEDs. The module is all one, and partially transparent as the PCB has cuts in it between LED rows. Looks sexy but makes service harder.

    Each module has around 210 precision phillips screws, so that's 1680 or so per frame. BUT, one of the things that rusted the most was some of these screws. And I need to remove the plastics to replace LEDs.

    Looking around, I found powered screwdrivers for precision bits and all that, so that exists. I can put it back together with half as many screws or less. I figure I can hit them all with oil and maybe clean them up a bit -- as long as the + is still there the screws usually come out but a few are worse. I can drill those.

    I was thinking of maybe getting some SMALL tslot and wheels and it could be possible make a jig for LED replacement, and for soldering down them with accuracy.

    All together, if I could get 20 of 24 panels working it would yield 25' wide by 7.5' tall, or 15' wide by 10.5' tall. 16 panels is still like 20' wide by 7.5' high!!! Pretttty sexy! But they are heavy, and with 8 in a case the cases are so heavy it's impossible to lift. They are set to stack but you would need 4 really muscular people to unstack I think.

    I love LED walls and it's awesome that the frames interlock, I even have 5 of the hangbars (really could use 8 of them total.)

    Unfortunately the system was made by a company in China and they are out of biz, so the odds of getting replacement modules is left to surplus market and they're not as common as the ones you see from Aliexpress (that I built my P10 display from.) Control system is Novastar receiver cards, and I bought a sender so that has been dealt with mostly.

    Some pics of it in action. You can see the LEDs stuck on when it's black. There are others that are out, that is easier to deal with though.

    https://imgur.com/a/C8jAR7i
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  2. #2
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    So you're contemplating replacing all of the bad LEDs one by one? That seems like an incredible amount of work! Plus there's no guarantee that you won't have further failures down the road. (Unless maybe you can "bake" the panels in a low-temp oven for several hours to drive out any residual moisture.?.)

    I agree that having a huge LED video wall would be great, but based on the pictures you posted and the module size of 40x40, I'm guessing that 1/3 to 1/2 of the modules will need to be removed. (So 60-100 modules, times 210 screws per module... That's a shitload of screws!) Then there's the challenge of removing and re-soldering all of the bad LEDs, and of course they are surface-mounted, which is another challenge all by itself.

    More power to you if you have the time and motivation to tackle this one, dude, but I think I would be running for the exit by now.

    If you can figure out a way to desiccate the panels somehow (heat lamps, maybe?), I would suggest trying that first to see if it cleans up any of the stuck LEDs.

    Adam

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    Quote Originally Posted by buffo View Post
    So you're contemplating replacing all of the bad LEDs one by one? That seems like an incredible amount of work! Plus there's no guarantee that you won't have further failures down the road. (Unless maybe you can "bake" the panels in a low-temp oven for several hours to drive out any residual moisture.?.)

    I agree that having a huge LED video wall would be great, but based on the pictures you posted and the module size of 40x40, I'm guessing that 1/3 to 1/2 of the modules will need to be removed. (So 60-100 modules, times 210 screws per module... That's a shitload of screws!) Then there's the challenge of removing and re-soldering all of the bad LEDs, and of course they are surface-mounted, which is another challenge all by itself.

    More power to you if you have the time and motivation to tackle this one, dude, but I think I would be running for the exit by now.

    If you can figure out a way to desiccate the panels somehow (heat lamps, maybe?), I would suggest trying that first to see if it cleans up any of the stuck LEDs.

    Adam
    Yea, I have one of the flight cases with damp rid and a fan in it right now. Set it up last night. Easier than trying to bake modules or something strange.

    I think all of the modules would be removed. It's pretty wild the way it's made up. There are 6 #2 screws that hold a module to a frame for rapid replacement in the field, but then the module itself to get the plastics off to replace components have the 210 or so tiny phillips. I started a spreadsheet, and started labelling the panels so I can keep track of status of each one. I was noticing realllly bad corrosion on some of the tiny screws, that isn't good. I can get away with skipping a lot of them for replacement and drilling them out, but I need some of them to be usable.

    Yea. Had the banquet hall manager not pushed it outside or if I found it right after it was discounted then it would be in much better shape.

    I was thinking of making a jig for replacing the LEDs. Though the videos online from the major manufacturers just show hot air against the back replace SMD LED on the front. I was thinking a T-slot jig with solder tweezers that have blade tips or something.

    My goal was to rent it out, then eventually buy a better one. Might be ewaste. It still looks kinda fine doing video but anytime there is a solid color ... ooof.

    Hmmm will research baking.
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    Wonder if you could build an x/y table to automate the LED replacement process? Thinking of something that operates like a commercial pick-and-place robot for PCB manufacturing.?. If you have to place everything by hand, you'll need a very steady hand.

    Could you use a heat gun to loosen the solder so you can pull off the bad LEDs? Or would that risk damaging the PCB?

    If you have a small drill press you could build a jig with multiple stops to make it easy to drill out the bad screws. But buying anywhere from 12,000 to 20,000 new stainless steel screws is going to be painful...

    Adam

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    Quote Originally Posted by buffo View Post
    Wonder if you could build an x/y table to automate the LED replacement process? Thinking of something that operates like a commercial pick-and-place robot for PCB manufacturing.?. If you have to place everything by hand, you'll need a very steady hand.

    Could you use a heat gun to loosen the solder so you can pull off the bad LEDs? Or would that risk damaging the PCB?

    If you have a small drill press you could build a jig with multiple stops to make it easy to drill out the bad screws. But buying anywhere from 12,000 to 20,000 new stainless steel screws is going to be painful...

    Adam
    Yea that is what I was thinking. I have an unfinished CNC router in the garage that is made from really thick Bosch Rexroth T-Slot. I never finished it, but it has NSK ball slides and I have a Gecko 4 axis driver, K2 CNC 5" Z axis for Bosch router and right at start of covid I had custom 10mm ball screws (faster travel over 5mm) made in China for it. So in theory it could be used to do some stuff and I think the work area is like 18" x 30" or so.

    The way the commercial companies tell you to replace their LEDs is using a hot air tool under the PCB and then pull the failed one off and replace on the top:

    ----

    Here a dude hot air removes then hand solders in replacement (outdoor coated):
    https://www.youtube.com/watch?v=rdGMmxhhJwc

    I would have put solder down on one of the 4 pads, heat it, place the LED, then solder in the other 4 so it sits flat -- that is how I do the two lead surface mount capacitors. Did that all the way through Amiga 4000 tower motherboard and it came out really good, as with a Sega Nomad handheld and many others.

    ----

    I have a SMD rework hot air thing, cheap one but I've used to it to replace SMD chips like DAC on a Gauntlet Dark Legacy (Atari Vegas 777 board) and a Motorola 68030 quad flat IC on a Mac IIci and stuff. So I can go that route I think. I replaced the diodes on my Lightspace Pluto driver.

    Not sure if it would work but solder tweezers mounted on a XY thing that could pick would be cool. I think a real PnP machine uses air to move parts? But it could give stability and ease of alignment for replacement. And could be done with small cheap T slot and rollers or delrin guide. Wait, I might already have all the parts needed sitting in the garage to build this from some other 80/20 tslot that someone gave me. Hmmm.

    But yea, automating this for repair would be the way to go. The guy that sold the system to the dude I got it from, he wasn't cool. He has 200 of the 40x40 modules but wants $250 each for them (uh, yea, no.) Meanwhile my inbox is full of catalogs from China so I have an idea of what the low end of the market is. Someone else one FB said they had parts and to DM them, I did, then no reply. So maybe someone else jumped on his comment and intercepted my potential help.

    The screws are really tiny precision ones, and aren't stainless steel (that is why they rusted.) I should be able to get a huge amount of new ones? They are plastic screws -- I will try to caliper them out, but they are tiny!!

    Challenges :-)

    16 of the panels working mostly well would still be massive. 7.5' high x 20 feet wide.

    Another question is how to figure out the best replacement LED candidates if buying new. I know they won't match due to the others having aged and all that, but it doesn't bother me that much for my use (you can usually only tell when there is flat colors, video and visualizers hide it.)
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  6. #6
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    Turns out I guess the moisture penetrates the SMD LEDs and damages the junctions. This may lead to it causing issues in illuminating all the time when the array is scanned? So I get a bunch of sets of 4/5 LEDs that stay on.
    Damage to the LEDs themselves shouldn't cause LEDs to stay ON. That sounds more like a problem with the driving circuitry. I'm not super clear on how the whole tiles are put together from your description, but I would certainly look at the driver circuitry first, assuming it's separate from the LED array components. Maybe swap some of the LED modules between tiles and see what happens.

    If you do end up needing to replace any LEDs, I think you're going to get it done faster by hand than trying to automate it. Pick-and-place machines use suction to pick up parts, but they don't include any kind of soldering capability. They're meant to place new parts on stenciled blobs of solder paste or dots of glue, so they're a ways off from being any help for you here. Solder tweezers may or may not help, depending on the style of LED and the shape of the tweezers you have, but it's going to be one of those fiddly jobs that are hard for robots to do. Honestly I would just use hot air to remove them like shown in that youtube video, then probably clean the pads and apply small pillows of fresh solder (you need less solder than you think!), apply some no-clean paste flux, and then use hot air to solder the new LED into place. The paste flux will protect the solder from oxidation so you can preheat it before placing the LED, and once the LED is gently pressed down into place it should self-align from the surface tension of the molten solder fillet.

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    Very cool and hope you get it done and post when you are finished.
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    very slowly pull a vacuum on the boards, but make sure no oil from the rotary pump gets on the boards, so install a trap.

    Atmosphere is 760 Torr.

    Drop to say 700 Torr the first day.

    Drop to 600 Torr and hold one or two days.

    Drop to 500 Torr and hold one or two days.

    Check function.

    One of the things of being a hobbyist pulling a vacuum is implosions are possible. This takes thought and care in the design of the enclosure. Suggest a heavy walled plastic bag.

    Lab Desiccators are cheap but take a few days, generally are a well-sealed glass or plastic bowl with science grade Dessicants.

    Do not pull a full vacuum on a board instantly, any remaining water in the components boil, at not much below 600 Torr. Controlled leaks are done with Humboldt Hoffman Tubing Clamps Fixed Jaw; Opening: 0.75 to 1 in. (19 to | Fisher Scientific

    If you check, there are bake protocols for components. However, you need a really good oven controller with rate of rise/fall controls for that, not SWMBO's kitchen oven,


    Tend to agree it is not the water, but corrosion.

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