Technical

I'm not quite sure if this is the right place to post this, but another club member suggested that others in the club might benefit from hearing about my resolution to a problem regarding a sticking motor assembly on an A4. To explain, I recently purchased a Dwight D Eisenhower which had been described by the seller as tested on a rolling road in the past but then stored - so he wasn't actually saying that it had been recently tested. Anyway, when it arrived I put it on test and found that it heated up without any problem but that was as far as things went - when I tried to open the steam valve nothing happened and there was no sound of the servo motor running in either direction.

Anyway, after a bit of testing I found that there was no voltage getting to the motor and that the PCBA relay was apparently faulty. As everything else about the loco appeared to be good I decided (in liaison with the seller who provide a small refund) to keep the loco and try to fix the problem myself. So, my first course of action was to replace the relay. Having done that, the motor started to run - success, I thought, but that was short lived because the motor would only turn very briefly before getting stuck (therefore drawing more current - which was probably why the PCBA relay blew in the first place). I then found that I could physically release the armature (rotor) with a small flick but when I tried to change the direction the same thing would happen. I spent a lot of time looking for mechanical solutions to the problem in the gear chain but eventually concluded that the problem was actually with the motor itself.

Although, when the armature was spun manually it operated fairly freely, I discovered that it only got stuck when powered - strange! So, I dis-assembled the motor to try to find the cause and found that the magnets, which are held to the steel frame both by magnetism and double sided tape, were capable of being lifted because the tape was no longer doing it's job. My conclusion was that when the motor was powered the magnets where lifting fractionally and binding the armature. To fix the problem (see attached photo) I've araldited the magnets in place and expanded the steel frame slightly so there's no chance of the armature binding on the magnets. I've given it a good testing and it seems to be fine now.