MK2S Issues and solutions on both kit and pre-built
I thought I would list out some issues I've encountered with and without solutions.
1. Bubbling of heat bed PEI.
I recommend waiting till the bed cools to remove parts and change the location of printed parts on the bed when possible.
I also found a thin pizza cutter is the best tool for removing parts to reduce bubbling as it allows me to walk around the part. I also use a simple spatula I designed and printed to remove debris that stick to the bed and a plated spatula for suborn thin calibration strips. I only use the pizza cutter for prints as its thin and allows me to work around the part to release it rather than pry it up. And of course prepare your PEI surface before prints.
Early on bubbles did occur before I adopted the pizza cutter and became large enough that i was able to apply pressure to one side and drag them to the right side of the heated bed to release the air pocket. This worked for a while till the PEI sheet suddenly tore off.
When you replace the PEI sheet Limonene (Pure Grade) is your friend. There are plenty of other write ups on how to replace it.
http://manual.prusa3d.com/Guide/Replacing+the+PEI+sheet/133
I found it easier to leave the bed on the printer and protect everything around the heat bed from Limonene and the bed glue that scrapes off.
Be careful but thorough when scraping as you can remove the thin top paint coat like it did.
2. Ghost PINDA searching.
The the PINDA (inductive sensor) seemed way too high when searching. After replacing it I found it had a short in one of the the wires. I suspect it was at the union of the extruder housing to the x-axis carriage.
https://photos.app.goo.gl/8dOyloAwFx5Lg6VJ2
3. Broken soldered heat bed connection.
Prior to a thermal runaway and total failure the heat bed may start taking longer to heat up. At one point I had a certain position along the y-axis the bed would turn off. Eventually the inverse occurred and only one position along the y-axis supplied power to the bed.
Since the failure seemed to happen from stress on the electrical wire I ended up re-soldering the connection, inverting the cable support, wrapping the contacts in the electrical tape and zip-tying the heat bed wires together to create a larger strain relief. 
https://photos.app.goo.gl/5KWBOsec3RyxBErw1
4. SD card connection issues.
A while back i notice the SD card on one printer wasn't being read , for some reason the printed cover was not fully seated and was applying a pressure away from the SD card contacts. I ended up removing the cover and has worked great sense. Then my pre built had the same issue and i found not inserting the SD card on that printer resolves the issue.
5. LCD blank screen and power off.
I believe it was after replacing the PEI sheet. During xyz calibration part way complete the LCD display would flash and shut off. I tried restarting it and was able to repeat the same thing after several attempts I traced it to the 5A fuse on the rambo. Labeled "F3" in the following in the link 
6. Extruder plunged into the heat bed mid print.
This issue I have no solution for yet. I was performing a routine calibration print with a change in material when I came back to the damage. I had repeated the same steps pre and post this indecent and have yet to experience the issue again. I have a musical melody that plays to alert me when prints are starting, half way and at different phases of the print. After some time of not hearing the melody and being lost in work i found the nozzle plunged into the bed still on. Prusa support went though diagnostics with me and had no answer but guessed it was a glitch in the software.
Since the bed was dead I decided to expose the terminals on the back side of the bed and solder to the top terminals in series. This provided a complete circuit and the bed was able to pass calibration and reach full temp. Printing was possible.
7. Melted heat bed electrical connection to Rambo.
This was an issue I found when replacing the heat bed. Possibly related to the broken power cable at the bed. I suspect the issue was from strain relief on the cable going into the Rambo enclosure. Solution is the make sure the cable is zip tied to the rambo enclosure so the internal connection can not flex.
See the following link where I listed where you can find a replacement "molex 3953X" connector for the rambo.
https://shop.prusa3d.com/forum/original-prusa-i3-mk2-f23/heated-bed-connector-burned-crispy-o--t2414-s40.html
