Scored lucky with a 42" LCD TV

Discussion in 'General Electronics Chat' started by tom66, May 28, 2011.

  1. tom66

    Thread Starter Senior Member

    May 9, 2009
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    I bought an LG 42" 1080p LCD at the local "Household Waste Centre" (aka "the dump".) I paid £20 for it after it caught my eye. LCD panel is intact. Fault description: No power, not even standby power. Open it up... four dead 2200u 10V caps. :D:D:D Easy to repair (about £5 for 9x Rubycon 2200u 16V low-ESR), and it looks like the only fault. Some other caps might need repair.

    In a way, I like LG for using cheap Chinese capacitors (SAMWHA brand), because it means broken TVs are cheap and easy to repair. On the other hand... I hate it, because it means that you can't get good electronics these days. The problem seems endemic in the consumer electronics industry, and it doesn't look like it's going to stop.

    The fact that the TV is otherwise well designed (it even has surge absorbers on the input!) makes me worry that it comes down to the lowest bidder in terms of parts. Rubycon caps are used for the input filter caps, but not the secondary side. Why??

    Manufactured Feb 2007. Lasted a little over 4 years, ridiculous.
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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    Good deal for £25. Not much seems to last these days, I'm on about my 7th or 8th Freeview box, the last one that died was a HDD recording one.
    Found a 2A 24V power supply the other night in a skip, should come in handy sometime and it looks unused.
     
  3. DigitalReaper

    Member

    Aug 7, 2010
    70
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    A little off topic (sorry)... Is that the council dump you bought it from? Over here the staff aren't allowed to let you take anything, and (supposedly) instant dismissal for anyone that breaks that rule. They put up a bunch of CCTV and everything.

    So much for recycling... *sigh*
     
  4. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Yep, was the council dump. HOWEVER, they told me a contractor comes around to collect them 2pm every day. So the manager told me he would sell it to me for the same price said contractor pays - £20 - and they had me sign a form, so it seemed official. They stuck a sticker on it saying "untested, may be dangerous" and "for spares only".
     
  5. pistnbroke

    Member

    May 9, 2011
    32
    1
    samsung the same 42 inch power supply caps bulging...sold off on e bay about £200 then £7 to mend it
     
  6. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Replace them, it's easy with even a cheap soldering iron.
     
  7. EdGs

    New Member

    Mar 10, 2011
    17
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    Good job on the fix, those bulging caps are quite common it seems. I remember reading on the net about some sort of industrial espionage where the formula for the electrolyte was stolen, but it was an incomplete formula in that it was missing a corrosion inhibitor. Something like that. Apparently, millions of these caps with the bad electolyte were used and here we are now.

    I have fixed a few lcd monitors and such for this very problem, and its usually the offbrand caps like capxon, etc. Sometimes tricky to disassemble the monitors, but quick to fix, and cheap too. Nice find.
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I know where to go "shopping" for a nearly free TV now. :D Idiot consumer's loss is smart technician's gain.
     
  9. JJS1234

    Member

    May 26, 2011
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    WOW! Never thought of that.

    That was smart what you did. Now I need to look for a waste center! Why cant they sell them back to you? Some sort of liability thing?
     
  10. tom66

    Thread Starter Senior Member

    May 9, 2009
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    It's all got to be done by the book, put on record. I had to sign a form agreeing that the product may be dangerous as it is untested.
     
  11. tom66

    Thread Starter Senior Member

    May 9, 2009
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    I desoldered the caps from the power supply. It's quite easy, just apply heat to the joint, and rock the capacitor. Works best with a temperature controlled iron - I set mine to 450°C. So now I have four bulging caps removed.

    Out of curiosity I decided to test these caps. I charged a few to their nominal 10V working voltage. I then measured the voltage immediately after disconnecting the power supply. One dropped quickly to 8.5V and then began decaying at about 0.1V a second. Another dropped down to 6.5V immediately and followed a similar decay, but a bit slower, maybe 0.01V/second. Both are not good signs, so the caps are definitely bad.

    I've developed a hypothesis that this TV had problems before a complete power failure; that's why the primary caps are bulging as well as the standby caps. I'm thinking that it would have been switching on and off (or otherwise glitching) during normal operation and the owners lived with it. Over time, the caps got worse and worse, eventually leading to a complete failure of the standby and primary capacitors. We'll see if it is really that simple.

    Also tested the 8A and 5A fuses on the board and both are good. Had a good look around the board for failed components and found none obviously failed. If I had found a power MOSFET failed it would have been far more difficult to repair. But nope... just the caps. :D
     
    Last edited: May 29, 2011
  12. JJS1234

    Member

    May 26, 2011
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    Well I am going to call my waste center tomorrow see watsup and hopefully go down there and see if I can find anything.

    Though i dont think I will get anything with a cracked LCD/LED/Plasma display.
     
  13. #12

    Expert

    Nov 30, 2010
    16,321
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    The last time I tried to recycle at the county recycling center, they asked me why I was dumping 2 computers. I told them I fix the computers for my family, and these 2 died. The jerk in charge told me that this made me a business and refused to let me give him the old computers for free.

    So much for recycling... *sigh*
     
  14. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Tom, it might be useful to also test any opto isolators and the PWM chip on the board to the extent practicable.
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    now you are learning..............
     
  16. tom66

    Thread Starter Senior Member

    May 9, 2009
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    If it doesn't work I'll do a more in-depth analysis. But for now, I'm only replacing the caps. They should arrive Wed, Thurs or Fri.
     
  17. tom66

    Thread Starter Senior Member

    May 9, 2009
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    Not worth buying anything with a cracked LCD or PDP; that's the most expensive part of the TV. Even if I fail to repair this I can sell these broken on eBay for £100-£200, so I'm in for a win either way.
     
  18. tom66

    Thread Starter Senior Member

    May 9, 2009
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    I just checked in my local electronics store and they sell a nearly identical LG 42" 1080p for £730!!!! eeeek I don't wanna know how much this cost new!

    Caps should arrive Wednesday
     
  19. tom66

    Thread Starter Senior Member

    May 9, 2009
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    It works :D!

    It turns out the display is only 720p (actually 1368x768), but that's still an excellent deal for £20 + £5 in repairs! I'm going down to the dump later this week. I plan to have a look for a 1080p display. If I find one, I may sell the refurb 720p and replace it with a 1080p. :D

    Four capacitors were replaced and the display works with my computer as well as with the Sky box. (Which I am looking at replacing with a Freesat DVR. Guess where that is coming from. :p)

    I'm not particularly proud of my soldering especially one joint but it should be okay. One pad came off the PCB, but I soldered it to the extra paste applied on the trace, and the TV does work! :)
     
  20. JJS1234

    Member

    May 26, 2011
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    WOOT! Well thats good. I have one similar and I have done some research and am led to believe that it is the PSU. Im pretty sure I know not only what to look for or to replace because of what you went though (similar), but an online store sells a kit for this and posts pictures of what it was (the capacitors).
     
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