Well since this thread is not dead, I will share my experience when I repaired my Mpem last summer.
With the Mpem PCB sealed in potting compound, I had to find something to make the compound easier to remove. I took three pieces of compound which I carved out and sunk them in three different solutions: 1- Paint thinner (varsol), 2- Acetone, and 3- Lacquer Thinner.
1- Paint thinner: Didn't do nothing to the compound;
2- Acetone: Compound got a little softer but not that much and I was scared that the Acetone could damage some of the eletronic components;
3- Lacquer Thinner: Bingo! Compound was swelling and breaking up in chunks! Lacquer thinner is nasty stuff for your skin but it's pretty safe for metal and most plastics.
So first thing I did is used a dremmel to dig a trench about 1/4" wide all around the edge of the plastic casing between the casing and the PCB. 1/4" is about all you have of clearance between the PCB and casing wall. Don't damage your casing cause you'll need it again!
After digging the trench, I filled it with Lacquer thinner and let it sit overnight so the compound in contact would swell. The next day I was able to remove a bit of compound all around the PCB. You'll need to make yourself a special tool such as long thin blade not wider than 1/4" that you can bend 90 degree to an "L" shape so that you can get to the bottom of the casing and rotate in the compound between the casing bottom and the PCB.
It took me a week, every day taking a bit of compound off and adding new lacquer thinner until I was able to pull the PCB out of the casing.
After that, it gets much easier. You will need something like small wood carving tools to delicately carve out the remaining compound around the components but only remove what is needed around the components of interest.
There is really just one component that failed and that is the large Diode "MR2535L". However since I damaged the 470uF capacitor with my blade during the compound removal step, I decided to replace this one and also all of the 1000uF caps while I was at it since I didn't know if the Lacquer thinner could have infiltrated and damaged the caps.
After soldering the new diode and caps on the PCB, I covered the aluminum back plate with electrical tape (just to make sure I don't short any connections on the PCB) but I did put back the screws to secure the semiconductor backside to the plate which is used as a heatsink.
Then I plugged the PCB on the Traxter and tried it and everything was working! Then the last step was to seal back the PCB in the plastic casing and the cheapest solution is to get GE silicone II which is safe for electronic components and solder joint (no acid composition - no corrosion during curing).
The traxter is back on the trails and we even did a waterproof test (not intended!) when the traxter was in the water up to the handlebars and didn't stall and it didn't affect the Mpem which was completely under water!
Here's some photos with comments:
Picture 1 showing the 1/4" clearance (between red lines) between the casing side wall and the PCB.
Picture 2 showing inside of plastic casing after PCB was removed.
Picture 3 showing the PCB removed with still some compound on the components and the dead diode circled in red.
Picture 4 showing the PCB with most compound removed. You'll notice the 470uF cap on the right side of the dead diode that has been damaged while removing the compound with my thin blade.
Picture 5 showing zoom of the dead diode. This is a MR2535L.
Picture 6 showing zoom of the 1000uF caps which I decided to change because of the possible damaged by the lacquer thinner.
Picture 7 showing the beat up 470uF cap which I also changed.
Picture 8 showing the dead diode (MR2535L) removed from PCB.
Picture 9 showing new caps installed on PCB.
Picture 10 showing new diode installed on PCB.
Picture 11 showing zoom of new diode installed on PCB
Picture 12 showing PCB with Aluminum back plate reinstalled with spring clips to keep semiconductors (2) touching the plate for heat sink purpose. Note that I covered the backplate with electrical tape to prevent shorting any connection on the back of the PCB.
Picture 13 showing PCB back in casing and filled with Clear GE Silicone II which is safe for electrical components (non corrosive). Note that it took me 2 tubes of silicone to fill the casing and I have sunk the tube in 80 degree celcius water for 10 minutes to ensure the silicone would flow easily everywhere.
Picture 14 showing Mpem ready to go back in the Traxter.
Picture 15 showing happy kid on Traxter back from the dead and in the trails we go!