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Technika LCD Power Supply faulty...

Discussion in 'Troubleshooting and Repair' started by Coconut, Feb 28, 2010.

  1. Coconut

    Coconut

    3
    0
    Feb 27, 2010
    Hi, this (Technika M22/20A-GB-TCDI-UK) LCD TV supply trips when loaded , I've proved the TV is ok with a bench supply,perfectly normal.
    The power supply is a separate board , with a 12v and a 16v o/p.
    The 16v (no load) measures...16.0v dc.
    The 12v (no load) measures... 10.9v dc.
    I've checked the "cold side" caps (out of cct.)...all ok .
    The outputs (12&16v) have a common Gnd.There are two Schottky Diodes (MBR20100CT) on the output..when I test (sic.) these the voltage drop is only 0.286v is this normal for this type of diode? / How do I test it?
     
  2. Coconut

    Coconut

    3
    0
    Feb 27, 2010
    Hi, again sorry for the "silly " question about Shottky diodes found this...

    Schottky vs "standard" silicon diode

    Schottky generally has lower reverse voltage max. You can easily find silicon diodes with 200-1400v ranges, while commonly schottky is 20v-60v.

    Schottky is extremely fast recovery, even faster than so-called "fast recovery" silicon diodes. So you can use them in high frequency SMPS.

    Forward voltage drop is lower. In silicon you get 0.6v-0.7v at rated current. In schottky you can get 0.3v which is great for SMPS.

    Most schottky diodes look exactly the same is a regular diode.

    if you want to test a schottky with an multimeter, set it to measure forward drop and measure the drop of the diode if its 0.3-0.4 its a working schottky. (or a burned silicon....)
    hope this helps someone else...
    gotta look somewhere else for the fault..!
     
  3. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    The fault could be at the primary side. These PSU's often rely on a small electrolytic capacitor there for proper operation. If there's one near a controller IC I'd try to replace it. If you post a pic of it I could point out suspects.
     
  4. Coconut

    Coconut

    3
    0
    Feb 27, 2010
    Thanks...

    Thank you Resqueline for your prompt reply, the problem was the whole board .. it's mounted vertically AC (input) at the bottom... DC (smoothing caps) at the top... no holes in the heat sinks..typical---> so cap cooked.".rem. to make/ get an ESR measuring cct."
    All ok now.. Xbox /HD Tv , IPod cool , still no DVD player (what the hell he's off my back teenagers for ya!), "Lets get a new one dad"...if only life was that easy...
    Thank you for your web site.. it's good.
     
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