Cheap camera stepper motors faulty

[dr pepper]

I got a pack of 10 micro stepper motors off ebay a while back, they were surplus camera focus motors.

Eventually I had a use for one, in a aircraft instrument I'm adapting, so I pulled one out wired it up to a microcontroller running a microstep routine, worked fine, pulled another out, dead and another dead, and another dead, 3 out of the 10 work.
I'm getting open circuit on one of the wingdings, not always the same one.
So I'm thinking that these were probably a scrapped batch that fell into the wrong hands and ended up on ebay.
I'll dissect one and see where the issue is, it might just be a naff job cleaning the enamel off the copper where the leadout is soldered.

Edit: I forgot I had a pocket microscope, using it you can see it looks as though the enamel wasnt scraped off at all, so either its that weird stuff that solders through or they forgot to do it.

 

[alec_t]

Am I missing something? I see no wires/leadouts.

 

[gophert]

Am I missing something? I see no wires/leadouts.

Looks like a 4-wire through-hole design to me.

 

[dr pepper]

OK I'll explain that some more, there are 4 pins on the motor as you circled, these pins then have 40 guage or so enamel copper wires leading into the motor windings.
I suspect that where the windings wire is wrapped around said pin there is a bad connection, possibly die to the insulation not being removed first, or they used tefzel solder thru insulation that didnt work.
The intended application probably had a flexible pcb soldered to the pins.

 

[dr pepper]

I managed to get the remaining 3 into the guage chassis, but one fell apart and another went open circuit, I think I migth get some better motors.
Heres what I manged to get to work so far, the movements are not fantastic smooth as I'm controlling the motor with pwm not a current source, still its fairly accurate.