About two years ago, I purchased a supposedly mint condition LGB Euro mallett at the typically inflated prices these things achieve. This was one of the early models. Some wheel plating loss indicating usage plus a few cosmetic issues. Overall it still presented quite well (definately not mint) and at low speed/voltages, it ran superbly. Alas, when voltage increased the unit would short circuit and shutdown my 6 amp controller.
Today I finally decided to sort this thing out. Suspecting a motor was causing the issue, I removed the rear truck motor and sure enough the motor would stall with around 12 volts applied and short circuit the controller. I thought lucky me, I picked the dud motor. Not having a spare short motor, I modified a new old stock mogul long shaft motor to fit (quite simple operation) and installed it. It ran well so decided to finish it off and test again.
On test, the drive once again stalled resulting in a short circuit. OK out with the front truck. Sure enough it too would stall with around 12 volts applied. With only one more long shaft motor remaining in the kitty, I modified it and installed it to the front truck and tested it. It ran like a dream at all speed/voltage ranges. Locomotive now runs as it should have when I purchased it.
Back to the dud motors. Not having any spray solvent, I sprayed WD40 into the commutator area and after removing excess with air spray, I ran the unit. Of cause a lot of smoke, but no stalling. I ‘washed’ it again and dried it and ran for extended period at varying voltages. Startup amp draw was 0.10 and 0.240 at around 20 volts. I then turned my attention towards the other motor and achieved similar results. I will treat these ‘repaired’ motors as suspect spares.
I feel that at some period the drive units were overserviced, contaminating the commutator, causing it to short circuit and stall. A lesson to be learned here.