also i have noted the solder jobs are piss poor i had a dead board just reworked the solder it was all ok then
but the very first unit i pulled out had a dead rx crystal so a process of elimination

i noted that the reciever board when you push down on it it would fire up ok as soon as you took the presure of it would die again so i reworked the solder and that fixed it
also had a problem with one motor would not go forward so i reworked the solder on the main larger board and that fixed that hmmmm
pays to have a good soldering iron for doing smaller electronics on hand