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Zener diode?

Discussion in 'General Electronics Chat' started by simon1979, Nov 22, 2016.

  1. simon1979

    simon1979 New Member

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    Hi all, I'm new here and would like some help. I have a PCB board off an appliance. I've noticed a zener diode(?) Is damaged. Does anyone know what value or number it could be? Hope the pic is clear enough. The damaged one is on the right Thank u. IMG_20161122_195909_230.JPG IMG_20161120_205155_785.JPG IMG_20161120_205155_785.JPG IMG_20161122_195909_230.JPG
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Zener diodes usually have their voltage printed on the casing, so a blurred picture without any writing on it offers no clues.

    A picture of the entire board might offer some clues?, as would knowing what the zener actually does?.
     
  3. simon1979

    simon1979 New Member

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    I can't see a single thing printed on them . I can put a whole pic up of the board. A new PCB from aga/Rayburn is nearly £700!
     
  4. dave

    Dave New Member

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  5. simon1979

    simon1979 New Member

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    IMG_20161122_202506_295.JPG
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Why such blurry photos? It's not that difficult to hold a camera still. Set it on something if you have to, but the pictures you are providing are not helping at all.
     
  7. simon1979

    simon1979 New Member

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    Ok taken some more pics will upload
     
  8. simon1979

    simon1979 New Member

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  9. simon1979

    simon1979 New Member

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  10. simon1979

    simon1979 New Member

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    All diodes are is copper colour and a single black band around the centre.
     
  11. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Welcome to ETO, simon1979!

    Tough PCB to find, but:

    upload_2016-11-22_17-40-18.png Source: https://www.aga-spares.co.uk/index...._id=1315&virtuemart_category_id=76&Itemid=495. A Rayburn "Sequence Controller".
    No schematic that I could find.

    But from your pix, the diodes have been, obviously, carrying quite a lot of current. But few traces. Maybe zeners in series?

    Could you get a good, focused pic of the underside of that section of the PCB to help us see how they're wired?

    As for replacing them, and if they're zeners, I suspect that they're all the same value/type. What value may be tough to determine.

    <EDIT> Also, see this: (400G/L PX (PF): http://www.rayburn-web.co.uk/Prodin...urn 400GL PF instal 08-13 EINS 512531 (2).pdf - page 18.
     
    Last edited: Nov 22, 2016
  12. pfofit

    pfofit Member

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    Howdy.
    What makes you think they are Zeners. Elsewhere on the board, red circle, there is a zener clearly marked as zd1.
    They're not always labeled zd but if there is one marked zd then i would hope any others as labelled the same.
    Also what is all that stuff everywhere, it might be conductive ? Is it just dust? Looks like corrosion or carbon.
    What environment is it in? Either way needs to be cleaned up

    Cheers
    123.JPG
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    ZD is likely a Zener diode. D9 is likely a 1N4148 which is a common switching diode.
     
    • Agree Agree x 1
  14. JLNY

    JLNY Active Member

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    Maybe I'm completely wrong on this, but I'm not sure I can see any polarity markings on D4 or D6? Are we sure they aren't surge protection diodes of some kind?
     
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    Could be. Odd that they're stuck off all alone the way they are.

    And the heat signatures around them certainly indicate a lot of heat.
    Good catch, pfofit.

    So, anyway, could use a pic of the underside for the traces. Might at least show how they're wired. Need a really close look at the the "diodes", whatever they are.
     
  16. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    What are the wires coming out from beneath the diodes? What do they go to?

    I expect these diodes are, indeed, some sort of protection diode, be it TVS (transient voltage suppressor) or even just flyback to protect against voltage spikes when an inductive load switches off.

    That whole board needs a good cleaning. Get some isopropyl alcohol and a stiff-bristled toothbrush to clean it off.
     
  17. simon1979

    simon1979 New Member

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    Yes will give a good clean. Tha nks for all the replies! I'm beginning to think I've rub markings off the diodes! And they are diodes not zener diodes! Will get a pic up later of underneath the board. I'm think the other diodes away from the area in question are the same type. They have 3 bands on them.
     
  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  19. Scott Marshall

    Scott Marshall New Member

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    Have you actually tested them? They may be OK, just dirty.
    I'm familiar with Rayburn (er) systems, and they are usually oil or gas industrial heat exchanger burners. (I spent a few years in a potato chip plant as plant engineer, and subsequently have run an industrial controls business)
    The oil burners especially produce so much "gunk" it's often attracted by electrostatic charge and will occasionally make components look burned when they are in fact, only dirty. The pattern around the diodes looks like this effect.

    I've seen a pair of series diodes used as a flame out indicator before as well, and wonder if that may be the case here. (they react rapidly to temperature changes). Does that board tab face the burner thru an opening in the burner box? If so that may be the function of the diodes. Rayburner always held onto old tech way past it's prime, as the diode flame detector was a very 1940-50s kind of technology. Then again I could be totally wrong with that assumption...

    Hope I helped a little...

    Scott
     
  20. simon1979

    simon1979 New Member

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    IMG_20161123_190958_190.JPG diodes in another place on board
     
  21. simon1979

    simon1979 New Member

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    Underside of board
     

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