junghans ato w-726a stopped working

[richardh]

i recall a similar issue with another member which pointed to a transistor failure. i'm not sure if it resolved the issue but if anyone has any guidance it would be gratefully recieved

[JohnBayley]

Are you still looking for help on this? I'm working on one now and have learned a couple of things that might help.

[richardh]

Yes still looking at this. I’ve not bought the transistor yet. Any tips?

[JohnBayley]

You can do a simple test to check if the electronics are basically working.

You only need a 1.5 volt battery, a multimeter and a couple of clip leads.

Connect the clock movement, battery and multimeter (set to a low milliamp current range, we are trying to see short 2 milliamp pulses), in series, being careful to get the polarities right.

Once connected, there should be zero current shown on the meter (a few microamps perhaps, but way less than a milliamp). Then start the balance oscillating. If the meter shows any current activity the electronics are probably ok. If you see no indication of current flow then either the transistor is dead or one or one of the coils is open circuit. If the drive coil was shorted you might see current pulses but I think that would be fairly unlikely.

When running properly you would see a series of pulses abound 20 msec long, 200 msec apart, each of about 2milliamps. On an analogue (moving coil) milliammeter you should see some flicks from the needle. On a digital meter the digits will probably jump around. 

I have an oscilloscope and just measure the voltage across a 22 ohm resistor in series with the battery when testing. This has the advantage that the shape of the waveform gives me a good indication whether there is adequate amplitude in the balance swing.

Someone else has posted ATO-MAT info on the forum, in the "All things Clocks" area. Have a look at there. I think he posted circuits too.

[Kalanag]

9 hours ago, JohnBayley said:

…Someone else has posted ATO-MAT info on the forum, in the "All things Clocks" area. Have a look at there. I think he posted circuits too.

https://www.watchrepairtalk.com/topic/28134-junghans-ato-mat-wall-clock-repair/?do=findComment&comment=237002

Edited December 25, 2023 by Kalanag

[richardh]

many thanks for the replies. i'll take a look and see how far i get. much appreciated.

[richardh]

i changed the transistor at cost and its still not starting and running. there's not many parts in this movement so i'm not at a loss. any ideas welcome. many thanks

[nevenbekriev]

What is the resistance of the coils?

[Kalanag]

Given

- the era of this electronic circuit and

- the fact that there is no bias resistor for the base current and

- the operating voltage of 1,5V only

let me assume that a germanium transistor is needed. A modern silicon transistor might not work at all.

18 hours ago, richardh said:

i changed the transistor at cost and its still not starting …

It should be mentioned that the early versions of this movement are not starting by itself. You have to push the balance with the integrated lever.

Edited February 17 by Kalanag