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Repeated blown capacitors (LCD TV Inverter board)

  • 07-12-2014 1:08am
    #1
    ciotog
    Registered Users, Registered Users 2 Posts: 670 ✭✭✭


    Would appreciate your thoughts on next steps for the issue(s) I currently have with my LG 37LY95 LCD TV.

    Symptoms: TV comes out of standby; screen is blank but sounds plays. For awhile beforehand I'd had to turn tv on/off several times before I'd get a picture then all was well.
    Attempted Repair: Read various guides about examining boards for visibly failed components, particularly capacitors. Found two capacitors with signs of slight bulge and leak (https://flic.kr/p/oV9479). Some searching and I sourced a reasonably priced replacement board on eBay. Installed it, powered up and got a picture (hooray!). Powered down and fully reassembled the TV. Powered up again and there was flickering a slightly odd humming noise and a return to a blank screen. No return to life. Opened up and the same two caps on the replacement board are now in a similar leaking state.

    Lots more searching and pondering along with debate of trying my hand at soldering :) What I'd appreciate some thoughts on is: The caps blowing again indicates another problem with the TV (not just the original caps failing after several years of usage) but I don't know what. The only conclusion I can come to (which may well be wrong) is that they would fail because of a surge. That could be (I reckon, anyway) a problem with the power supply board feeding the inverter board or the lamps connected to the inverter board. Visual inspection of the power supply board doesn't suggest anything blown there. I see a power supply board on eBay for ~£30 so I can try that along with replacing the caps myself on either of the two inverter boards I now have but wouldn't mind taking a more educated approach :)
    Tagged:


Comments

  • #2
    CountyHurler
    Closed Accounts Posts: 8,657 ✭✭✭CountyHurler


    Symptoms: TV comes out of standby; screen is blank but sounds plays. For awhile beforehand I'd had to turn tv on/off several times before I'd get a picture then all was well.

    On first reading my thoughts would be.... Sounds like there is a problem with the inverter board, or the power supply feeding it... I would shine a torch on the screen. If you can see the proper image (to match the sound) with the torch, then you have established that it is an issue with the illumination of the image, the backlight... This is more to rule out issues with the LCD panel transistors / tcon / main board... so that you can focus on the inverter/backlight/PSU

    I would then look at the secondary electrolytic capacitors on the power supply and test the transformers and MOSFETS on the inverter board.... I would also check the voltage that is coming out of the DC 24v (?) rails that feed the inverter board.. (You could try a dummy load of 2 12v bulbs to see if the PSU is working properly)... But a lot of the time the damned CCFL bulbs in the screen are just bad... They can act erratically, and are very difficult to replace...

    Had I been faced with the bad caps that you were, I would have just replaced them (rather than buying the full board)... They are cheap and easy to replace... Out of curiousity I would have tested the capacitance and ESR of the old caps to see if they were hugely out of spec and likely to be causing the fault...

    Having said all of that, I would have thought there was a 70-80% chance of you getting a fix with the new board... so you were probably a bit unlucky with that...


  • #3
    ciotog
    Registered Users, Registered Users 2 Posts: 670 ✭✭✭ciotog


    Thanks for that. Will look at the tests you've suggested (I'm not particularly missing the TV - watching what I want to see on a monitor). Buying the board is down to not having a soldering iron - it was £30 on ebay. As there are a couple of jobs I could do around the place with one, will invest over Christmas.


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