Replicator MightyBoard Protection: Part 3 - LCD Board by garyacrowellsr

Last crawled date: 3 years ago

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.