Identify Triac from Varilight lighting dimmer switch

Discussion in 'Electronics Repair' started by SparkyPete, Dec 21, 2016.

  1. SparkyPete

    SparkyPete

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    Hi folks.

    Managed to repair a touch-activated table lamp after a bulb blowing stopped it working. On that occasion I found an online article about replacing the triac with a BT139, with greater surge resilience.

    Now the Varilight wall switch dimmer has failed in the full-on mode after a bulb failure knocked it out, as well as tripping the lighting circuit mcb and house rcd.

    So I cracked the dimmer open and managed to get what I believed to be the triac off the pcb. Unfortunately, the numbers on the triac make no sense and I have tried googling them in various combinations, but nada. So I'm wondering if you know the answer or where I can find it.

    Here are the details:

    In two little circles on the top of the device - 03 and K4

    First line - DT1X PJA1327 B2

    Second line - 3798

    I understood triacs usually included the characters BT134, 136, 139 etc, but maybe not.

    Any ideas or suggestions greatly appreciated.

    Thanks all.

    P.
     
    SparkyPete, Dec 21, 2016
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  2. SparkyPete

    Bluejets

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    I mostly use BTB08600B triacs.
    Easy to get, cheap on eaby (handful for a couple of dollars and work ok)
    Even used them in desklamp touch dimmers.
     
    Bluejets, Dec 21, 2016
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  3. SparkyPete

    SparkyPete

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    Thanks Bluejets.

    I'd just like to get confirmation that I have a triac in the part number I quoted and what its spec is.

    P.
     
    SparkyPete, Dec 21, 2016
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  4. SparkyPete

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    A dimmer is unlikely to use anything other than a triac. That said, to confirm it, if the part number can't be confirmed, you need to trace out at least part of the circuit.

    Dimmers are generally pretty simple circuits.
     
    (*steve*), Dec 21, 2016
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  5. SparkyPete

    SparkyPete

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    Are the pin-outs the same from one triac to another? If they are then I guess it doesn't matter too much which one I use to replace it.
     
    SparkyPete, Dec 22, 2016
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  6. SparkyPete

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The simple thing to do is to trace the power from the mains to the lamp. This will pretty directly go through 2 pins of the triac. The remaining pin will be connected to other stuff.

    If you can identify the pins and the package then you can see if the potential replacement triac (we're assuming it is a triac) has the same pinout.

    If you can upload some clear photographs of the device, including both sides of the board then we may be able to do this for you.
     
    (*steve*), Dec 22, 2016
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  7. SparkyPete

    73's de Edd

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    Sir SparkyPete . . . .

    Your original unit is being a DT1X triac of a design made by Philips w.a.a.a.ay back in the 90s.
    (Pre sensitive gate days)
    Their current equivalent replacement would be a BT138 with its spec of 400V @ 16A
    If you want a little more headroom peak voltage cushion , they also make a BT138-600 version .


    73s de Edd
     
    Last edited by a moderator: Jan 4, 2017
    73's de Edd, Dec 22, 2016
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    SparkyPete likes this.
  8. SparkyPete

    SparkyPete

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    Fantastic - thanks de Edd - although this dimmer was bought new only two years ago!

    I've now managed to take some pics, so maybe you could confirm if the pinouts are the same as a BT138? I've been recommended the BT139 previously and used that successfully - would that do - readily available on Ebay UK, where I am?

    [​IMG]

    [​IMG]

    [​IMG]

    Thanks for your help - much appreciated.

    Peter
     
    Last edited by a moderator: Jan 4, 2017
    SparkyPete, Dec 22, 2016
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  9. SparkyPete

    SparkyPete

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    Hi all.

    Well, I replaced the triac with a BT139 and it made no difference.

    Original symptom persists: as soon as you press the pot seutch the light is on at full. Varying the pot makes no difference.

    So, could another component be at fault?

    The triac cost as much as the whole switch more or less, so this is more of an academic exercise.

    Thanks

    Sparkypete.
     
    SparkyPete, Jan 4, 2017
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  10. SparkyPete

    shrtrnd

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    I'll jump in here with off-topic input.
    Dimmers used to be easy with incandescent bulbs. Now there's so many bulbs in use, CFL, LED, in a wide variety
    of configurations. All of them designed to run directly off the mains. Few of them designed specifically for dimmer
    applications. Your triac may be taking a hit from a problem in your circuit, or the circuit might be incompatible with
    whatever bulb-type configuration you're using. (A lot of THEM have their own internal circuitry)
    Like you said, I, would just replace the switch. But since you're experimenting, I'll let you get back to input
    from all the experienced other guys here.
     
    shrtrnd, Jan 5, 2017
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  11. SparkyPete

    SparkyPete

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    Should have mentioned bulbs are incandescent.

    Have already replaced the switch, just excercising my curiosity as this is the second such switch taken out by an incandescent bulb failure in my house in the last couple of years.
     
    SparkyPete, Jan 5, 2017
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