Timex Electronic from the junk pile

[HectorLooi]

57 minutes ago, AndyHull said:

Bear in mind that the output would be 110 or 240 V AC, and might give you a bit of a whack if you are not careful.

No problem. I have experience working with 1000V vacuum tubes and 60kV transformers. Lost count of number of times I gotten shocks. 

[AndyHull]

A typical electric clock consists of an asynchronous AC motor and a gearbox to drive the hands.

https://en.wikipedia.org/wiki/Electric_clock#Synchronous_electric_clock

Asynchronous motors are not particularly fussy about the input voltage, however they run at a more or less fixed rate, due to the way they are constructed. If you look at one of those old fashioned timer plugs, the electromechanical ones, they work the same way. So the output voltage needed to drive the motor might not need to be too precise, so if it is a little low, that may not affect the rate of the clock. A little high, might cause the coils to overheat, but a little low within reason might not have any measurable effect. Obviously if the voltage drops way too low, then there would not be enough energy to drive the motor.

The accuracy of the clock depends almost entirely on the accuracy of the main frequency, rather than its voltage.

What this means in practice is that you could probably pull an ancient 12V transformer based wall wart apart and use the transformer from it. Modern wall warts are smaller and don't use the same type of transformer, they use a switching regulator (switched mode) design.  The secondary would be fed by your switching transistor, with a current limiting resistor, and that in turn by your 555 sine wave generator. The secondary of the original transformer becomes the primary in your circuit and vice versa. Bear in mind as I said before you would produce sufficient current at approximately mains potential to give yourself a bit of a whack if you were not careful, so treat the output the same way you would a live mains circuit.

The output would be approximately correct, and probably close enough to be functional.

Edited December 12, 2020 by AndyHull

[AndyHull]

There are other ways to produce a nice clean sine wave of course.  DDS function generators pcb are cheap as chips on ebay.

https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=dds+signal+generator&_sacat=0&LH_TitleDesc=0&_sop=15

 

https://www.ebay.co.uk/itm/ICL8038-DDS-Signal-Generator-Module-IC-DIY-DC-12V-25V-Sine-Square-Triangle-Wave/273264014504?hash=item3f9fcdf4a8:g:yWwAAOSwQb1bF5Vm

That way you can run your clock at any speed you like... If you want to extend your lunch hour... slow it down. Time dragging in that meeting.. speed it up...

[AndyHull]

Armed with total control of the frequency of your "mains", you could go for the Lord Vetinari approach to time keeping.

Quote

Lord Vetinari also has a strange clock in his waiting-room. While it does keep completely accurate time overall, it sometimes ticks and tocks out of sync (example: "tick, tock ... ticktocktick, tock ...") and occasionally misses a tick or tock altogether, which has the net effect of turning one's brain "into a sort of porridge". (Feet of Clay, Going Postal). In Feet of Clay Vimes observes that it must have cost him quite a lot of money.

https://www.instructables.com/Lord-Vetinari-Clock/

 

 

[HectorLooi]

The watch stopped again this morning after working fine for 2 days. I noticed the the second hand spins when I tried to adjust the time. This means that the sweep wheel click is not locking properly.

Looks like I have to do a full tear down and check the click spring.

I hate reassembling Timex Electrics and its variants. There are just so many pivots to persuade into the pivot holes. I wonder how they did it in the factory. 

[Tic]

I have a 40 movement and the wire is fine, but no joy on the coil. Contact pin to coil back to balance wheel is somehow gone. 

I don't have anything to magnify so I can see the wires of the coil in enough detail. Anyone fix a coil before?

[HectorLooi]

No. I think your best option will be to get a donor watch. I'm not sure if the balance from other calibres will fit the M40. Perhaps JerseyMo will be the best person to advise you.

[JerseyMo]

go with a donor or NOS part