Hmmmm weird one coz not 101% sure if it has a fet or not to go pear shape
(not up on the latest G&G's I'm afraid)
http://guay2.com/web/gc_product/CM16_FFR_A2.php?lang=en
does have a mosfet
http://guay2.com/web/gc_product/FFR12.php?lang=en
does not seem to have a mosfet in stock tube
if its still under warranty and before you rip her open, talk to the dealer/place you bought it from is best advice
if the motor connected to G&G FFR still doesn't spin out of grip or half out then something has blown on the wiring side
or on the trigger switch side....
The fet could be blown (G&G fet's are the most robust ones in the past) but can't 101% sure if it has a mosfet
yes you could run a few tests on wiring with a multimeter but what you are testing depends on fet or no fet
in theory if fetted then it would have red/black plus at least one extra thin wire at rear of receiver - stock tube
(doubt if G&G mounted a tiny internal fet), and you should see an extra block on wiring loom in the tube as well as fuse
if it isn't fetted then you will just have red/black wires running to gearbox.....
testing for any breaks on posi wire first - battery end to motor connection
pull trigger and complete circuit or continuity should take place - if not switch is w@nked perhaps
(was you running her nutz on 11.1v that might start to burn trigger contacts)
or the trigger/switch mechanism may have failed - doubt if it is one of them super duper electronic mofo units or it would of said like on SR range
also check negative wire too - but this would be switched if fetted
the thin red signal wire should work fine testing for continuity on posi lead/trigger switch
as I say - depending on if she is fetted or not but it seems she ain't fetted if I got model correct
I'm trying to determine if the mosfet is blown - but if she ain't got one then it can't be that
trying then to test if the trigger switch is borked either burnt out or a mechanical failure
I would deffo look into contacting the retailer if at all possible first
failing that then maybe ask somebody at ya site who maintains the rental guns so you can save on postage and be kept updated whats wrong etc....
sounds either wiring, mosfet module or mechanical inside the box if trigger switch failed
but a few further tests would help narrow it down to what exactly went pear shape
please contact retailer first is my best advice and use any warranty you might have
if s/hand maybe ask ya site's techy guru mofo next
soz I can't help ya more atm