ATO Troubleshooting transistorized ATO clock

Discussion in 'Electric Horology' started by clockspot, May 17, 2016.

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  1. clockspot

    clockspot Registered User
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    #1 clockspot, May 17, 2016
    Last edited by a moderator: Dec 29, 2017
    Hello!

    I recently acquired a transistorized ATO regulator (my first of this type) whose pendulum doesn't want to go. Its transistor is labeled TJN1, which looks like an early French germanium PNP transistor (source, source).

    Attached is a circuit diagram. I think it's roughly equivalent to this one, the closest I could find online - only with a PNP transistor, connected on the other side of the battery accordingly.

    I've effectively disconnected the coils and transistor for testing, and it seems the transistor is the culprit - both the drive and sense coils show resistance, and the transistor gives no reading between what appear to be the base and emitter (red wires in picture), using a multimeter in diode testing mode like so (I know just enough about electronics to be dangerous).

    Can anyone confirm whether I'm testing it properly, and/or suggest a possible source for a suitable (both electrically and aesthetically) replacement transistor to try?

    Thank you in advance!
    2016-05-02 10.46.39.jpg 2016-05-16 22.38.00.jpg 2016-05-16 22.46.34.jpg

    2016-05-02 10.46.39.jpg 2016-05-16 22.38.00.jpg 2016-05-16 22.46.34.jpg
     
  2. rogerj

    rogerj Registered User

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    Hi..according to this site :https://sites.google.com/site/transistorhistory/Home/european-semiconductor-manufacturers/history-of-transistors-in-france The TJN1 is a very early NPN, germanium, low power,low gain AF transistor. As such I would think almost any low power germanium transistor will work.
    PNP germaniun are much more common but a quick search on eBay for "NPN Germanium" threw up quite a few - and cheap enough to try.
    Assuming there are no other electronics in the clock a PNP transistor such as an OC71 might work if you reversed the battery (this is something I might try rather than suggesting it will work !)
     
  3. praezis

    praezis Registered User

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    I understood, it is just the other way: TJN is PNP:

    Frank
     
  4. rogerj

    rogerj Registered User

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    #4 rogerj, May 17, 2016
    Last edited: May 17, 2016
    Thank you for correcting me Frank..Don't know how I managed to swap that after returning to the thread..So, as the OC71, or perhaps OC72 are PNP transistors they might make suitable substitutes without changing battery polarity - and they are readily available .
    so..DON't search ebay for "NPN Germanium", search for PNP. Roger
     
  5. Tinker Dwight

    Tinker Dwight Registered User

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    If the transistor is changed from pnp to npn, as well as the battery
    reverse, the wires to the coils need to be swapped as well.
    With the transistor disconnected from the coils, one should see
    a diode on the C-B and B-E.
    Other that open and shorts, germanium transistor fail by getting
    a high resistance base to emitter lead.
    Tinker Dwight
     
  6. clockspot

    clockspot Registered User
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    Thank you everyone! I now have a couple of NOS OC71 on order, and will update when they come in.

    Dwight, your description of the germanium transistor failure seems to fit my test results.

    Luke
     
  7. clockspot

    clockspot Registered User
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    I'm happy to report that replacing the TJN1 transistor with an OC71 did the trick, and having been cleaned and oiled, the clock is ticking away happily. (The supplied homemade battery holder is to be replaced.)

    Unfortunately I couldn't leave well enough alone and tried to remove a bit of residue from the dial, with a bit of water... and the paint came right off (just above 9 o'clock) which has rather taken the shine off the repair. So if anyone with a similar clock comes across this thread, learn from my mistake and don't touch the dial!

    cc7efb0a-ade5-4f8f-9e36-3dab7e95dbd6.jpg 6cff69dc-22bd-40b9-b284-f7d07a6371f8.jpg 8310a6ce-eb58-4e7f-b7f9-5c54448c2249.jpg
     
  8. Tinker Dwight

    Tinker Dwight Registered User

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    These are cool clocks. It is a good thing the transistor
    is not part of the coil like the Kundo clocks. Most newer transistors
    have steel cases. This causes the magnet to wobble at the coil.
    Tinker Dwight
     

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