Care to share photos of dissasembly and mosfet replacement?
It needs more than just a few pics to explain how to do the procedure, but here some of pictures I took.
It is quite difficult to remove the PCB with heat spreader from the case. After removing the 2 bolts, you need to pick out the sealant, especially where it touches the case. Once much of the sealant was removed, then I found that by pushing a small screwdriver under the PCB, on the same side as the cable entry, then the whole assembly is released a little. Then if you firmly pull on the phase wires, the whole assemble starts to lift out. Once it starts to move, it comes out quite easily, but it is a bitch at first and you need to pull quite hard.
When removing the fets, you need to be careful, not to damage the PCB or let any of the nearby SMD parts fall off. The fets butt up tight to the PCB, so you can either carefully break each fet (with some big cutters), leaving the component legs, which can then easily be extracted 1 at a time. The other option is to heat all 3 legs of the fet and extract each fet in 1 step, but you do risk damaging the PCB when you do it this way (happened to me). Maybe with more practice, the right temp on the soldering and the right tip, this could work well. After wrecking a PCB trying to extract the fets in this way, I went with chopping the fets up and that worked out. The large Cap, needs to be removed as well, in order to remove and fit some of the fets.
I suggest the PCB is confirmed functional, after removing the fets, but before it is built up with the new fets. Ensure there are no shorts between any of the pads on the fets. Do not try to run the controller, just connect it, power on and confirm the display is not giving an ER30. If there are no errors, chances are, you should be able fit the new parts and it will likely work. If you get an error, unlucky.... you must have damaged something, or lost an SMD component. Watch for static too, that can kill this type of device.
When building it back up with the new fets, I fitted about 4 of them (leaving the bolts loose), to the heat spreader, then fitted this to the PCB. Next I dropped in each of the remaining fets into the PCB and then loosely fitted the bolts, securing them to the heat spreader. If you solder the fets to the PCB first, the heat spreader will not line up. The fets need to be fitted to the heat spread (with bolts lose), before you solder them. Once everything is soldered, you can tighten the bolts and fit the large Cap. Before proceeding, check there is no continuity, between the base of each fet and the heat spreader.
When you fit the new Fets, do another continuity test, to ensure there are no shorts. You can beef up the traces and add another 5mohm shunt (as shown below). With the additional shunt, the controller will provide 45A, when you program it with 30A (1.5*). Fingers crossed, you should now, have a functional 45A BBSHD controller.
Like I said, I am not suggesting everyone goes out and does this, as there is a very big chance, you will wreck a perfectly good controller. If you do get it to work, it will put more strain on the motor (battery too) and you shouldn't then expect this modified motor to be still covered under warranty. These motors are designed for ~1500W max, not ~2200W max, so don't be too surprised is something breaks, or whine about it, if it does