Repair + Service: Elgin electronic 105 – calibre 250 / Junghans 600.10 ato-chron

Torsten from Hong Kong sent me a whole batch of watches – and this great looking Elgin 105 electronic is one if them. It doesn’t work any more, but he sent a long another Junghans 600.10 for parts.

Elgin used the Junghans movement for this watch. It’s an electro-mechanical movement, based on the principles invented by Leon Hatot (that’s why Junghans called these movements ato-chron – ato from Hatot, chron from the Greek chronos = time). The idea is to provide the moving force for a watch or clock by accelerating the pendulum or balance wheel with a coil that pulls a magnet. So no winding, and an electronic watch that is almost entirely mechanical.

The movement is completely encased in a shield made of sheet metal to protect it from outside electromagnetic influence. The gray bit at the bottom holds the coil and simple electronics. The coil consists of two coils, and the balance wheel is magnetic. When the balance swings, it excites the first coil, which switches the transistor, which opens and closes the circuit to the second coil, which pulls the balance wheel. The balance wheel is started by the hacking seconds lever when the crown is pushed in.

The electronic unit with the coil visible.

The balance wheel has a permanent magnet, which makes it a lot heavier than a normal balance wheel – one of the problems with this type of movement. There is a lot more wear on the balance pivots, and the watch is more prone to change its beat rate when moved.

If you follow the balance bottom jewel outwards, you see the Junghans star – the only indication that the movement wasn’t made by Elgin. Click on the photo to enlarge it and have a look at the pallet fork. The movement works “in reverse”. Instead of the pallet fork accelerating the balance, here, the balance moves the pallet fork, which moves the gear train. So there is almost no wear on the whole gear train. Also, check out the shape of the escape wheel. Again, it’s driven by the two pallets on the pallet fork, rather than driving it, so its shape is completely different.

The rest of the gear train is as usual. You can see the brass lever for the hacking second.

The bottom plate doesn’t give much away – apart that there is no provision to wind a mainspring.

As you can see, not a great amount of components. Off to the cleaning machine.

Time to put everything back together.

With the grey coil / electronics assembly from a donor watch and a new battery, the balance starts swinging straight away.

The dial and hands go back on.

Pretty cool watch. You’ll want one of those for your collection!



12 thoughts on “Repair + Service: Elgin electronic 105 – calibre 250 / Junghans 600.10 ato-chron

  1. Bit late coming to this party…… very interesting read. I just acquired a part watch for spares with an Elgin 250 movement but with a Matthey Doret case and dial. Interestingly the movement serial number is very close in production to yours (131812) and appears to be to all intents and purposes a Junghans 600.10 movement, having the same train bridge, which is different on the later 600.12 and 600.30 variations.
    I used the electronic module from this to resurrect a Matthey Doret watch with a 600.30 movement. I found that the height of the hand tubes on the Elgin movement is higher than the same wheels on the 600.30 movement, making the hour wheel too tall to fit on the 600.30 movement, leaving no room on top of the cannon pinion tube to attach the minute hand (guess who picked up the wrong hour wheel when assembling the Matthey Doret watch) so I assume that this is because of a thicker dial on the Elgin watch or is it just the same as ‘genuine’ Junghans 600.10 movements and different on the .30 ones?
    The fact that the movement serial numbering on the bridges seems to run consecutively through different ‘makes’ (some stamped ‘Junghans’, others stamped ‘Sheffield’ and even these ones stamped ‘Elgin 250’) of movement suggests that they were all made at the same time in the Junghans factory?
    Again a very interesting series of watches to collect, the Matthey Doret now joins my 600.10 Sheffield :0)

  2. I have one of these Elgins with the 250 (Junghans) movement. It is complete however it doesn’t seem to be getting the electrical connection. It will run on its own for about 10 seconds when the crown is pulled out and pushed back in. Do you service these? I am based in the USA.


    • Looks like the coil or the electronics are damaged. It only swings as pushing the crown in moves the balance to start up the watch. I am afraid I don’t do electric watches any more.

  3. Very well put together, both the watch and the article. I need an electronic unit for one of these, and the battery plate and rear case. If anyone could help I would pay the going rate. Also, a minor cosmetic point, but my 105 has the most amazing 9-facetted crystal – smooth on the top but prismatic underneath. I hate to think how long it would take to find one of these.

  4. What a great looking watch! And a really fascinating insight into electronic watches. I’m seriously jealous and will be keeping my eyes open for similar examples.

  5. Christian,
    Thank you so much. Good to see the Elgin working again. The second marking on the main plate “A9” indicates the year of production. The “9” stands for 1969. With regards to the letter is could be the month of production (January) not sure there.
    The markings are in line with those on all other mechanical Junghans in-house movements. The only difference being that here it is hidden under the balance. They are usually in plain sight next to the balance. (See the J89 for comparisson).

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