Cybergun Thompson problem. Advice needed

does the motor run if disconnected from the gearbox mechanically but still with the wires attached? if so then it's internal to the gearbox.you are in luck if the motor does not run because all the electronics on the thompson(version 6) gearbox are external so you dont need to strip the gearbox to get at the electrics,the trigger switch is held on with just two screws then just lifts off.so if its electrical you can remove all the electrical parts to fiddle with.
the other fortunate thing is its a version 6 gearbox and the easiest box to work on,im not going to do a full strip down guide for the version 6 gearbox but i'm sure a quick surf will give you a comprehensive guide.good luck

I completely disconnected the motor from the gearbox and ran two wires direct from the battery to test it. It's fine. It doesn't run when wired up to the gun. Without knowing too much about these, I imagine that pulling the trigger completes a circuit which activates the motor. The fault must lie in the trigger mechanism somewhere. Does that sound right ?

is there a fuse in the stock,the Tokyo Marui ones have a fuse,sounds obvious but worth a look.then it must be the switch behind the trigger at fault ,try removing the trigger assembly its only 2 screws and test the circuit again,if it dont work then its the switch burnt out,if it miraculously works then it may be a bent cut of lever,its the thing that re-sets the switch when on semi and can be seen as a lever about 2 inches long on the left hand side of the earbox that ends inside the trigger switch assembly,the lever can bend jamming the switch or it can break.

The fuse is fine. I'm not going to do any more tonight as there are some many tiny screws to lose and without natural light I'm bound to lose some. Thanks for the advice. I'll investigate further tomorrow and post back.

Many thanks for your help. Got it going tonight. I cleaned up the connections in the trigger mechanism and that did the trick. It was pretty fiddly to get the innards back into the lower receiver. Unfortunately it's only firing on full auto now but at least it's working. I might have another look in a few days. At the minute I'm sick looking at it !

those trigger units are fiddly inside,probably worth having a really good look at the cut off lever to see if that caused all the grief.yes sometimes you just have to put things down and leave them for a bit.