Hi
Yes 100% fets, for a long time on here I have been advising folks not to run more than 60V on Pumas (BMC) motors without upgrading the fets in the controllers, I blew 2 x controllers on a BMC at 72V, its also worth checking those little insulating tubes, follow fechters guide, on my Bullet proof controller i fitted 150V fets, i also used fet insulating pads and tab washers for all of the fets, I have run this controller on a Puma at 72V for over a year now and it has not put a foot wrong!!
Follow Fechters thread when you do the re-build, watch out for those pesky gate resistors as well as they blow, use your DVM and check all of them, you can sometimes blow the gate driver, change all low and high side transistors, they are so cheap its not worth taking the risk, don't bother with phase fuses, they are not quick enough to catch a blown fet, just use them on the main battery supply.
Its funny as all my blow ups were like yours, relatively low load but high rpms, I blew one just by lifting the wheel off the ground and showing someone how quick it span up! crazy.
Good luck with fixing the controller, I have fixed lots of them so give us a shout if you struggle, you can buy those surface mtd resistors in strips really cheap as well, if your eyes aren't that good you can piggy back them over the blown ones, my technique for holding them in place is using some blue tac, roll it out in to a long thin tiny sausage then stick the resistor to the end of it, you can then using the other hand simply dab the iron on to it, works really well.
Knoxie