Accutron Coil Testing

Discussion in 'Watch Repair' started by Time2Fish, Apr 4, 2017.

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  1. Time2Fish

    Time2Fish Registered User

    Mar 5, 2017
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    I purchased a 214 Accutron on ebay and am taking it apart. I have removed the coil and want to test it. I am pretty sure it is bad because the watch did not hum. I understand that I need to measure the resistance of each coil to see if it is good or bad but I don't know where to measure. Below is a photo of a 214 coil similar to mine. I put 2 arrows on one side where I think the resistance needs to be measured but I only have 1 point on the other coil. Any help would be appreciated. View attachment 339126
     
  2. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    I'm assuming you checked the voltage of the battery and have the correct one. Did you give it a couple of taps at the 3 or 9 o'clock position to see if it would start? I haven't looked into the best place to check the coils yet, and mine is a 3 wire coil.
    My first suspects would be the transistor and components. I'm not an expert on Accutron's yet, but in electronics checking coils with a resistance test is not the most reliable way because the resistance test can be misleading. You need a ring tester. I have a Blue Ring Tester but would have to modify it before using it on an Accutron because it uses a 9V battery.
    It looks like someone already replaced the transistor. The original transistors that I have seen are the old can type.

    Robert
     
  3. Time2Fish

    Time2Fish Registered User

    Mar 5, 2017
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    Thanks Robert. I did put in a new battery into the watch which I had verified was good. The photo above is one off ebay of a refurbished coil so you could very well be correct in saying that the transistor had been replaced. I have seen several threads which talk about testing coils and Samantha has said that it should be obvious where to measure the resistance. It is not obvious to me. In addition, The Accutron Service Manual I have says that if there is no hum, to check for a Mechanical Blockage. The watch was pretty dirty so I would not be surprised if there was a blockage, which is why I contend that the coil could possibly be good. Continuing on with my learning curve and having tons of fun.
     
  4. Skutt50

    Skutt50 Registered User

    Mar 14, 2008
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    I am no Accutron expert however in general, to measure resistance, you need to disconnect one side of the coil or you will measure the resistance of the entire circuit.

    I have not seen the schematics of this circuit but there may be some known values to be expected when the coil is still installed.
     
  5. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    Here's the schematic. The battery completes the circuit.
    http://members.iinet.net.au/~fotoplot/214ll.gif

    Robert
     
  6. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    As you can see from the schematic, the 2M2(2.2 Megohm) resistor & capacitor are wired together in parallel. One of their ends ties into one side of the feedback coil and the other side to the gate of the NPN transistor. The transistors emitter pin ties into the negative side of the battery. The resistors collector pin ties into one side of the D2 drive coil, and the other side of D2 ties into the side of D1 opposite the side that ties into the feedback coil.
    If you look real close you should be able to see how the tiny wires are coming out of the coils. The positive battery terminal will be the one that connects to the side of D1/F1.

    Robert
     
  7. roughbarked

    roughbarked Registered User

    Dec 2, 2016
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    The thing about accutron coils is that they must be kept at operating temperature to induce longevity. The fine copper strands can fracture within ambient temperature change ranges otherwise.
     
  8. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    IMHO It shouldn't be that big of a deal as long as the temperature changes aren't sudden and/or frequent.
     
  9. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    I checked the manual for the Blue Ring Tester and it's safe to use on the Accutron. It only outputs pulses of 600mV. You can get one here:
    https://anatekinstruments.com/collections/anatek-blue-ring-accessories
     
  10. robmack

    robmack Registered User

    Jun 22, 2013
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    Based on the schematic and your picture, I would guess the following test points are available to you.

    [​IMG]

    To test D1, probe both common points. To test D2, probe between D2 and its common point. To test F1, probe between F1 and its common point.
     
  11. robmack

    robmack Registered User

    Jun 22, 2013
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    One other advice - if you find yourself needing to test these small circuits often, it would be sensible to invest a few dollars in a good set of probe tips for your meter. I bought a "Fluke TP920 Test Probe Adapter Set" from Amazon and highly recommend them. This set has a great pair of tip extenders that terminates in a needle point, great for probing high density SMD circuit cards and small electronic circuits like this Accutron coil set.
    [​IMG]
     
  12. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    Yep! When I buy something I usually buy all of the adapters and extra goodies that I can.
     
  13. Alastair E

    Alastair E Registered User

    Jul 4, 2016
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    #13 Alastair E, Jun 10, 2017
    Last edited: Jun 10, 2017
    Wow!

    You guys make Such a meal of checking the coils!

    NO need ever to use ring tester on these, they aint Flyback Transformers! Ive NEVER seen a coil on Accutron go S/C windings, Always they go Open Circuit.

    Easy No Fuss-n-Nonsense Way--

    Std. multimeter a cheapo digital one will be fine.

    In fact, Any old ohm-meter will be OK, providing it'll measure 20K resistance. Doesn't matter how much voltage it puts out, most are between 0.1V and 0.7V anyway. Even that POS from 'Walmart!'

    Set to 20K ohm range or Auto-range--if its posh enough.

    Measure resistance between the two metal straps that pass along the plastic under battery molding.
    --Reading should be around 7-8.5K Measure at a point halfway along those strips.

    What you DEFINITELY DONT want to do is go probing around the three solder blobs right close to the coil itself, the coil wire leads there are often badly coated with varnish and are VERY easily broken. I Always revarnish all my coils to protect 'em from moisture or slight mis-haps like that, as over time the original coating develops micro-cracking A while ago, there were some SEM images on WWW showing the cracking to the varnish of Accutron coil-sets, cant find it now, prolly long gone.

    So--Thats the cell coil done. (Both F/B And drive sections checked for continuity,--At The Same Time. If one is O/C it really doesn't matter which, you'll get OL reading on meter and the coil is stuffed, Time to find another.)

    70% of time if a coil is O/C it'll be the cell-coil thats gone (closest to battery--and its leaks!)

    Now to the Comp. Coil.

    Test between Red Wire (whether its at the cell-coil end, or the comp coil end, doesn't matter) and the Collector of Transistor, (the wire that goes from the Tr to the pin on the coil plastic ledge.)
    --Should be around 7K... If O/C time to find another.

    Usual cause if both these above tests are Good, is Resistor and Capacitor need replacing--nice easy job on a two-wire like above. Ive done dozens of 'em!

    Whenever I rebuild a 214, I Rebuild the coil-set too, NO point whatsoever in leaving 50 year old junk in there, to fail a few months or couple of years down the road to disappoint everyone.

    Rarely--Very rarely, the transistor may fail, These are Military grade Raytheon transistors, so are good stuff.....

    These coils are Really Not as fragile as some guys make out, Temperature differences certainly don't make 'em fail, Abuse, physical damage--like bunging in battery all wrong or wrong type, Moisture and battery leaks do,

    Neither does the higher voltage of a silver-oxide damage 'em!

    BTW--That image from ebay you mention is of a refurbished coil--What utter rubbish, its got the usual old junk parts in it, carbon compo resistor and that hideous Tantalum cap, the Raytheon black-ball transistor is the only good part in there!
     
  14. Accutronica

    Accutronica Registered User

    Nov 21, 2016
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    I'm sure you're right about most Accutron coil problems resulting from open circuit, but the simple things rarely happen with me. A ring tester can find problems that a DMM won't - and I already have one, so why not use it. Besides that, I'm just learning anyway.
    I don't think I would call a component that has lasted for 50 years, junk. But I agree with you that if you are going to replace components, use high quality components.
    My 214 is a 3-wire. I haven't messed with a 2-wire yet.
     
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