does the magnet now lock on as soon as you turn the machine on?

the only thing i can see that could be wrong is the capacitor C1 has gone short  . But that shouldn't blow the transistor.

Replace C1 and do a diode check with your multimeter (with the wires disconnected) on D10 and see if it's faulty.

once you have replaced the cap and checked the diode try it again with the led hooked up as before in the test and see if the led turns off with the transistor connected. do this with out the fuse first and if the led turns on and off fine then try it again with the fuse.

If i had it here i would be testing it a bit differently, I would be bench testing it and substituting the coil and +50 volts for a 12 volt led lamp and +12v to save blowing transistors one after the other but I have the all the test gear here which makes things a bit different. I am not suggesting you try this, it just makes it harder to fault find when you are not set up for it.

what resistance is across the coil?