Replicator MightyBoard Protection: Part 3 - LCD Board

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From Part 1, we know that Replicator MightyBoards occasionally blow up. In that Thing and in Part 2 we corrected some problems and added some ESD protection. However we haven't done anything about the LCD board yet, so in this Thing we are going to address some of the issues there. There are several problems with the LCD board: There is no ESD protection on any of the signal lines that are routed on the LCD ribbon cable. The 3.3V regulator for the SD card and associated electronics is located on the MightyBoard - over a foot away on a poorly configured cable. This will result in very poor Power Integrity for these circuits. There is no bulk or bypass capacitance for either the 3.3V or 5V supply lines at the LCD Board. This will result in very poor Power Integrity for all of the board circuits. The level conversion for the SD card signals is 'iffy'; not something I'd do on a commercial product. The organization of signals on the ribbon cable is very poor, resulting in poor Signal and Power Integrity. Frankly, I'm surprised that it works at all. So, the question is: Short of replacing the entire board, is there anything we can do to correct these issues? The answer is the LCD ESD board presented in this Thing. It's not going to be a perfect solution, but it's going to go a long way to make the LCD and SD card function a lot more reliably and add some ESD protection. The LCD ESD board plugs into the ribbon cable connector on the back of the LCD board, and the ribbon cable plugs into it. Here's what it does: Adds ESD protection diodes to all signal lines. Adds a local 3.3V regulator; the MightyBoard 3.3V regulator is ignored. Adds bulk and bypass capacitance to the 5V and 3.3V rails. (Not a perfect location, but many times closer and more effective than the nothing that was there before.) Adds proper level conversion of the SD card signals, and adds some termination components that may improve Signal Integrity. Not much we can do about the cable organization, but we can add a simple clamp-on ferrite filter that might help some. Instructions It's always a good idea to practice good ESD (Electro-Static Discharge) prevention around your Replicator at all times, regardless of any 'protection' you may have added: ESD Prevention Avoid wearing clothing that generates static electricity. Avoid placing your Replicator in a carpeted area. When approaching your Replicator, touch something grounded before you touch the Replicator. Be aware that low humidity conditions can increase ESD problems by a factor of 10X. Also be aware that unpeeling just about any kind of tape generates an enormous static charge. It wouldn't be a bad idea to wear an anti-static wrist band when working on your Replicator. (Note that so-called “wireless” or “cordless” anti-static wrist bands are a hoax, and are less than worthless for preventing ESD damage.) To be effective, the wrist band must be grounded. Prelude: In addition to this Thing, you really need some means of covering the back side of the LCD board. Unfortunately the excellent Replicator Keyboard Cover will not fit over the LCD board with the LCD ESD Thing attached. With no other alternative at the moment, I must recommend the Replicator Front Panel. Besides enclosing the LCD board, it makes the LCD much easier to read in most situations. In addition, I strongly recommend that you have installed the aluminum tape ESD shield described in Part 2. You can install this Thing without it, but I really believe it will be less effective. I will detail this alternative in the instructions. And of course, I would expect you’ve installed the companion EndStopESD board from Part 1, though that isn’t a requirement either. Materials: You need an assembled LCD ESD board, or if you're building yourself, a bare board and the components listed in the bill-of-materials. With the included Gerber files, an order from OSHPark.com will get you three blank boards for about $7.50. Ribbon cable. 4-to-6 conductors; you'll need about 6 inches (~24 inches without the Part 2 tape). One crimp spade lug. (...and a ring lug without Part 2) One M3 (or M4) screw and nut, and washer. Tools: If building from scratch, you will need a small soldering iron, fine wire solder, flux, and other normal soldering tools. A magnifier will probably help. The surface mount assembly on this board includes a few very fine pitch parts - not impossible to do by hand but you should have some SMT experience. (Oven or skillet reflow would be fine too, if you know that.) Wire strippers/cutters. Drill and bit appropriate for a 3mm (or 4mm) screw. Allen wrench(s) to remove the LCD, Front Panel, Replicator bottom cover. Crimp tool. 25 - 40 Watt soldering iron, and solder. Dremel tool with cutoff wheel, or some other implement of destruction to make the cuts cuts in the Replicator case as described below. Skills: You will need to be able to solder a ground wire to the LCD ESD PCB. Make crimp connections. Drill a hole. Printing: Nothing to see here, move along. Installation: Sorry for the skipping around that follows, but I'm trying to accommodate two different possible Replicator configurations. You are in a maze of little twisty passages... If you have not installed the ESD shield tape from Part 2, and don't intend to, skip to step 4, otherwise, prepare a 4 inch length of 4-to-8 conductor ribbon cable by putting a crimp lug on one end and twisting the leads of the other end together. Solder the end of this cable to one of the 'ESD GND' points on the LCD ESD board. Drill a hole about 1/2 inch to the right of the case SD card slot, through the aluminum tape, so that it enters the build chamber. Insert a screw and washer into this hole, and lightly tighten a nut on the inside. Connect the GND wire from the LCD ESD board to this new screw and tighten the nut. Skip to step 5. Since you don't have the tape, you will need to make a long piece of ribbon cable that is soldered to the LCD ESD board at one of the 'ESD GND' points and running down through one of the corner cutouts and connecting with a ring lug to the ground screw that was installed in Part 1. Do not run this cable in parallel with the LCD ribbon cable. If you have a Front Panel Thing, skip to step 8. Otherwise, this part is simple. Remove the Replicator Keyboard Cover if you have one. Unplug the ribbon cable to the LCD board. Plug the LCD ribbon cable into the LCD ESD board. It is keyed and should only insert one way. Plug the board into the LCD board, in the orientation shown (i.e., it 'hangs' downward). If you had a Keyboard Cover, it won't fit now, so you can't replace it. I encourage you to find something to cover the exposed boards. Turn on the Replicator; the LCD display should come up normally, and the green led on the LCD ESD board should glow (though that's probably going to be hard to see.) Turn off the Replicator. Skip to step 13. Remove the Front Panel and unplug the LCD ribbon cable; the LCD board can stay mounted. This part gets ugly. The LCD ESD board, when mounted on the LCD board, extends into the front of the Replicator. It is necessary to cut out the vertical between the button and LCD, and cut out a sizable chunk out of the front and floor of the build chamber. Fortunately this will be covered by the Front Panel, and it's rear cover, so it doesn't have to be neat; but I'm sure you can do better than I did. (See picture). I grabbed a handy jig saw; I'm sure a dremel tool with cutoff wheel would be a better choice. Be sure to keep the ribbon cable and the LCD ESD board out of the way when you're cutting. Trim away the aluminum tape as necessary, but most of it (not shown in the picture) can be left in place. Plug the LCD ESD board into the ribbon cable in the orientation shown. It's keyed and will only fit one way. Place the LCD Front Panel in position and plug the ESD LCD board into the LCD board. Let it hang there on the cable for a moment and turn on the Replicator. The LCD display should come up normally, and the green led on the LCD ESD board should glow (though that's probably going to be hard to see.) Turn off the Replicator. Cut a notch in the right side of the Front Panel back cover to route the ground cable out. (Eventually I'll revise that thing to include the notch.) Mount the Front Panel and the back cover. The following step is optional, but encouraged. Remove the bottom cover of the Replicator. Unplug the LCD ribbon cable from the MightyBoard (you don't have to unplug the cable, but I found it easier that way). Place the two halves of the clamp-on ferrite filter around the ribbon cable, and snap on the two plastic caps. They all only fit one way. Plug the cable back in. Betcha can't wait for Part 4.