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suspect 13v zener in power supply

Discussion in 'Troubleshooting and Repair' started by [email protected], Apr 23, 2013.

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    [email protected]

    Apr 23, 2013
    i have Samsung LN40C610 2010 LCD the red led power light comes on but when you press power for set to come on it tries and doesn't power on.

    I confirmed that the power on [touch switch] generates 5v[A5v] to power supply Bd.
    I also get 13v [B13v] but only for a few seconds

    this B13v has a zener [which i suspect] but i can't get any more solder off it nor lift it to confirm 13v will stay [CN802 pin 1,2,3...

    i guess i could break the zener and hope my 13 stays n solder a 13v zener in later

    my question is how can i confirm zener is bad...i tried attach but too big

    schematic is:
    search: LN40C610
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Why do you suspect the zener?

    Have you suspected anything else (capacitors, say)?

    If you break the 13V zener, I can almost guarantee that the power supply won't work until you fix it.

    A photo of your power supply board would be useful (encode as jpg or png and reduce it in resolution and/or quality until you can upload it).

    [email protected]

    Apr 23, 2013
    just thought zener when i saw it on the 13v line

    hi Steve thx so much for reply, i used to fix stuff years ago and opened my big mouth, Yeah i used to fix fix my tv

    i managed to lift the zener today & put a 12v 1w in for laughs...not funny same no 13v

    so yeah maybe start pulling caps...also weird it txformer half [primary] on hot side p/s And other half [sec] on cold side...primary 2 windings 75v & -75v ok

    secondary few taps so 5v & 13v measure 0v...all windings/taps ck ok continuity
    here i pic of schematic, thz again steve i really appreciate it

    take care
    steve vancouver bc canada

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    hahaha yep.

    What were you involved in repairing? Are you familiar with switchmode power supplies?

    12V 1W as a replacement for 13V is not a bad idea. It won't give you the correct voltage, but if it improves things then it likely confirms a suspicion about the zener, and if not it probably gets a pass.

    From your measurements, it looks like there's no voltage appearing on the secondary of that transformer.

    You show voltages on the primary, but that may be everything floating at some similar potential above ground.

    The rest of the power supply on the hot side that you've not shown is likely to start with some filtering and then rectification of the mains into a capacitor. Following this the DC will be switched into the transformer. Typically there is a dedicated SMPS controller driving the transistor.

    Presuming that your past includes dealing with high voltages and mains connected equipment, I would then start by ensuring that the main capacitor has voltage across it. Typically this is in the region of 400V -- If I need to remind you that this could kill you, please stop right now :)

    The problem may be as simple as a shorted transistor that has blown the main fuse, but if this were the case I'd not expect to see any voltage present.

    The power LED is almost certainly being powered by a standby power supply that may be very simple, or it may be a separate low-power SMPS. It may be useful to see if this is independently fused, and also whether the voltage it is producing is within spec.

    I guess that's a few things I might start with.

    [email protected]

    Apr 23, 2013
    i wanna be a tech again

    thx again Steve, i see 15 on the zener number, but schematic 13v weird too
    shorted tranny maybe...also i get 13v for a few sec' a leaky cap [RC time constant to fail] but yes a shorted PN junction somewhere with an electrolitic in the mix

    i jus figure if voltage on primary [hot] and 0v sec [cold] my under load short near here
    no not too familiar with dc sw pwr/s. fuses all good...i will buy all caps tomorrow & replace
    i'll let u know how it goes

    thx so much, its been 20yrs since i have done repairs tv vcr audio micro mobile radio radar blah i'm feeling kindda weak now with this should be simple p/s problem

    Attached Files:

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