**Replicator MightyBoard Protection Part 1: ENDSTOP**
Replicator MightyBoards blow up. We know this because there have been at least a couple of dozen such reports on the Makerbot groups. There are certainly many more that we don't hear about, that are handled directly through Makerbot support. To date, Makerbot has handled board replacements very well, but given a choice, it would be better to avoid these blow-ups if possible.
By 'blow up', we mean that the 5V regulator on the MightyBoard really does explode, with a 'pop', smoke, and smell that's a pretty distinct indication that ***Something Bad*** has happened. There are several suspected causes for this problem, but one that is fairly certain is an instance of a short occurring in an endstop cable, resulting in a 'popped' regulator (see photos). This Thing prevents that type of short from destroying the board, and possibly avoids some other problems too.
This Thing is a small circuit board that plugs into the endstop connectors on the MightyBoard. The three endstop cables are then plugged into this board. The board does the following:
- A 1k resistor is added in series with the 5V that is supplied to each endstop cable. A short can still occur in the cable, but without the 'hard' 5V, all it will do is cause the endstop function to fail. Otherwise, the endstops will function normally, but the LED's may be dimmer.
- The MightyBoard 5V linear regulator is replaced with a switching regulator module. When the existing 5V regulator fails, it apparently applies 24V to the 5V rail, which destroys most of the components on the board, making it unfeasible to repair. Hopefully if a short occurs on the board, this switching regulator will shutdown gracefully, without propagating damage elsewhere. And, as a bonus, this reduces the power consumption, and waste heat generation, by about 3 Watts.
- ESD prevention diodes are added to the microcontroller endstop inputs. These might aid in preventing ESD damage to the Replicator, but it's difficult to judge how effective they may be.
- When this was started, it wasn't anticipated that the three unused endstop inputs to the MightyBoard would ever be used for anything, but that may change. Due to space limitations I didn't bring them out on the original EndStopESD board. However on this newer board I did bring these three endstop lines, plus a ground, out to a single 4-pin connector. It will take some creative placement, but a right-angle connector can be added there. It will have to 'stack' on top of some other components. 10K pull-up's have been added to each of these signal lines, so a simple switch closure to ground will toggle an input to the processor.
**Caveat:** This thing won't make your Replicator print faster, or make your prints look better. It's simply insurance against a small subset of the ***Bad Things*** that could happen to your MightyBoard. Worse, it involves some minor modification to the MightyBoard, which could void any warranty replacement of the board by MBI. However you should consider that in the not too distant future, your Replicator will become an unsupported 'legacy product', and replacement of your MightyBoard may become a complicated and expensive proposition. Up to you.
Also note that this Thing won't 'repair' a board that has already failed. You might consider adding it when installing your new board though.
This Thing is Part 1. In some following Things, I hope to patch a few more holes.