ETA 251.262 Magic Hands

[systeman]

Well, not really magic hands, just behaving rather strangely.

I serviced an ETA 251.262 out of a nice Tissot Martini Racing I'd acquired. The movement was very stiff and did not work. The small second hand was pulsating back and forth though.

It was very interesting though after the service and putting in the new battery. The sub dial second hand went backwards, as did the chronograph second hand. The sub dial split second hand worked correctly.

I stripped it down again, reassembled it and this time the big minute recording hand and large chrono second hand went backwards, but the sub dial second hand worked ok.

I stripped it down again and tested the stators up against a compass. Each one was magnetised but the polarity varied. I guessed it could only be that was causing the problem. I demagnetised each stator, drawing each one the same way up and away from the demagnetiser.

Now all the hands go clockwise, except the split second which isn't working at all now.

Oh what fun.

 

By the way, never use a demagnetiser on a quartz watch.

 

 

[rogart63]

I serviced a 251.262 recently. Had a hard time getting it to run properly . But it never run backwards. I changed the red coils 3 times. measured them and put them in . One of them was broken anyway. Even think i did managed to break one with voltmeter. 

Why did you demagnetize the stator? 

Check the coil for the split second.  Red should be around 1,8 to 1,9 ohm and grey or green around 1,5 i think. Also check the little black box thing . Make sure the screw is tight over that. 

Edited August 22, 2018 by rogart63

[systeman]

I had checked the coils before servicing and after reassembly. What I did find was evidence of polish compound in and around the crown and pusher tubes and between the case back and case. I think the previous owner must have polished the case using  dremel or similar machine. This was probably the cause of messing up the rotors and stators, regardless of the magnetic shield of the movement. Polishing as the cause was guesswork, but using the demagnetiser on the stators solved the problem.

It was indeed quite weird to see the hands turn in different directions, then only to be corrected after faultfinding. Then others that were correct to then go backwards. I put that down to not putting the stators back in different positions. The magnetic field the stators produced must have had an effect on the rotors. I'm guessing here, but as they were magnetised the polarity had an effect on which direction the rotors would turn. That's why I put them all on the demagnetiser a few times the same way up, and lifted them away all in the same direction.

I must say though, the stators did not demagnetise 100% ( probably a rubbish demagnetiser), but must have had an effect on aligning the polarity.

[Plato]

There's two types of stator: 4021 and 4021(1). The 4021(1) drives the rotor in the opposite way when energised. They look identical apart from a notch near the screw hole of the longer arm.

Neither type are permanently magnetised.

Thought I'd better share after putting a jigsaw of parts (eBay!) back together.