LCD repair


[Andrew] sent us this great breakdown of an LCD monitor repair. After his wife’s monitor developed an issue with rippling in the picture, he was forced to decide between trashing it, or fixing it. He decided for the latter, possibly to his wife’s disappointment. The rippling image could easily be attributed to a failed filter in the power supply. Knowing that capacitors are a prime suspect in these cases, he tore in, looking for failures. He found that there were, in fact, 2 bad capacitors on the back light circuit. After replacing them with newer, higher quality ones, the monitor was as good as new.

39 thoughts on “LCD repair

  1. Ha! I have done this a bunch, you could make a lot of money by affiliating yourself with a salvage business and repairing the monitors they have.

    On ebay you can get nice PC monitors for $50-75 (less shipping, which will add $30-50), if you could get ahold of those and fix them to sell for twice as much and split the profit with the outfit it might be a business case ;).

    I personally bought 2 Hitachi and a Planar (same product rebranded), and swapped parts into 2 working ones. Saving the extra parts I was able to replace the starting capacitors that burned out on a customer’s LCD.

    I wish that repair of things was more common (oh that? just junk it!), like the recommendation to throw away a PSU because the fan quit. I don’t, I solder in a new fan and keep on trucking. It is cheaper and more environmentally conscientious.

  2. I was recently given a Samsung 22″ widescreen monitor that has a fully working panel and PSU, but needs a new logic board (OSD ‘crashes’). But will Samsung sell me one? Will they hell…


  3. “how do you test the caps? my multimeter can read the value of caps… does the value read as something incorrect if the cap is bad? thanks.”

    I use an inexpensive LCR meter, looks like a DMM, but measures Inductance, Capacitance and Resistance. Picked it up from a surplus electronics website for < $50. I often wind inductors and transformers so I have to have something that does this job.

  4. Oh smokes where was this a few months back I just pitched an old LCD I opened it and found the rectifier had really dark almost burnt ends I went to radio shack and found the very same one installed it.. the monitor powered on then shut off immediately.. I suspected the capacitors which I couldn’t find a match anywhere ~ else online, so I said forget it and tried to sell it in a yard sale my poor mom kept phoning me when people asked about the note that said needed electrical repair bad power supply, the people who asked me about it pretended to know what I was talking about… embrace the hacking community no matter how big or small… cause everyone else are the people from another planet,,, not you,,, anyway I took the back lights out of the LCD to use on another project and pitched the LCD

  5. Many times you won’t even need a meter to know that caps are bad. Usually bad caps are visibly damaged. I had an old Celeron motherboard that I had replaced because of failure, recently got it out just to see if I could get it working and found that one of the caps had built up enough pressure to blow the bottom seal out, replaced it with a new cap and the board booted right up. Also have a DVD player that wasn’t working right, opened it up to find a leaking (vented) cap on the power board. Hooked a computer PSU to the DVD player’s main board and it ran fine, so I just need to get a new cap and that should work again.

  6. OMG, This is just like what I did, and to boot my name is Andrew as well, too funny. MY wife’s monitor just flat out quit and was putting out a high pitched squeal, I tore into it after buying a new one for her, I found 3 of the 5 capacitors in the power supply had popped their seals, I replaced all of the ones with comparable ones i had laying around. apart from a few modifications to the case shield it works like a charm, so i took it to the office and it’s been there for around 2 weeks.

  7. I’ve fixed a couple LCD’s, among others. Over some period of time during 2006-2007. a lot of bad electrolytic caps were shipped in a lot of equipment. They either don’t have electrolyte or have the wrong sort. They die fast. A lot of power supplies for computers and monitors used these for filtering. The ones I’ve been replacing, I didn’t even have to check: the top, which should be flat enough to reflect a spot of light, was puffed upwards like a dome.
    Most caps used in commercial/consumer goods are only rated to 20% accuracy or even worse, so your 33uF cap might measure 25uF and still be good, or at least as good as it ever was. I’ve seen plenty of caps sold 50% out of spec.
    Sanyo Oscon caps don’t have electrolyte. They have amazing lifetimes, as a result. They’re expensive, but if you want something to last, they’re a good investment. If you don’t want to spend that kind of money, any cap that a place like Digikey sells will give you a reasonable reliability, and better than the no-name or unheard-of caps that most modern equipment uses.

  8. The sad part here is that you almost have to fix this stuff yourself. The local repair shops generally lack the reverse engineering skills that are required to repair most electronic problems. Secondly if they can repair a device they charge far too much for the time and parts (which usually superceeds the device replacement price)

    This is a sad fact of our times.

    To cite an example i recently bought a bad Toshiba 48″ DLP HD TV for a price i could not turn down. Turns out the tv did not have any audio. After tearing in to the TV i found plenty of evidence that someone had tried to repair the TV. They snapped of a FPC lock (never hooked it up) busted off frame mounts, etc. After tearing the unit down hoping to find the FPC lock, i did find it and attached the FPC back to the daughter AV board. Suddenly i had noise in the speaker at high volumes but still no audio. From here i used some common sense. #1, The speakers still make sound so they are ok, The amplifier still work since it was driving the speakers. The digital volume control still worked since i could adjust the volume to a level of which i could hear noise. Most likely the only thing left is the MUX. I already knew where the mux was by looking at the numerous audio traces running back to a single chip. Turns out that the 11:3 I2C analog mux is fried, all inputs and outputs have 5vdc (checked the 5vdc power pins, they are fine) I suspect static or lightning damage.

    At any rate the DLP HD TV was bought and repaired for < $60.

  9. the place i work at just threw out a bunch of nice lcds and a big stack of laptops. such a waste. half the stuff probably still worked perfectly, but was simply replaced. they wouldn’t even let me take anything because they said it contained mercury, lead, etc. and would be a potential liability for them. :(

  10. My brother gave me 5 Dell monitors a year ago that had the exact same problems. The power supplies all had a bad pwm caused by a solder crack around one of the rectifier diodes. this is a very common fault on those particular power supplies. a $5, 5 minute fix and i was up and running. just replaced the pwm and touched up the solder on the whole board. i ended up selling all the monitors (minus the one i’ve been using the last year) for $30 each. split the profit with my brother and i’m happy.

  11. i can’t count how many lcd screens i fixed over the years, but near all of them had either a bad power supply or a bad cap in the inverter circuit. eventually i got lazy and just started strapping atx power supplies to the back of the ones with bad psu’s. they have the same voltages and can be founf everywhere :)

  12. for the low voltage lcd’s that have lost their power supplies, I make an adapter cable and put the same size of plug on one of the card slot filler plates for the pc, then wire that into the 12v+ and the ground that just plugs into the power supply, as long as the power supply is big enough, you turn on the pc and the monitor is powered up at the same time

  13. Fixing LCD monitors is quite often just a case of taking the back off and looking for burnt bits or dry joints. But it’s good to show people that they shouldn’t be scared of taking stuff apart I suppose.

    What draws me to comment is that title. LCD repair? No. The LCD wasn’t broken. Very misleading.

  14. I have a CTR Hyundai HCM-421E that i’m repairing now. It’s original problem was sometimes the screen get greenish and after a hand nock it returns normal. Any hints about this? or have someone the circuit diagram?

  15. kabukicho2001

    look for a cold soldier joint, basically were a component wire attaches to the circuit board, the metal heats up and cools down irregularly and causes the connection to break, intermittent contact is the result, you might need a magnifying glass to spot it, they can be tricky, I usually look for discoloration in the circuit board and concentrate my search there.

    Good luck

  16. this is a fairly common failure in lcds. i use to fix televisions for a warranty company. one of the first things we were to check on an lcd call was the caps in the power supply. caps will burst most of the time, and they will cause a wide array of issues with the set/monitor.

  17. Awesome! I very nearly trashed a nice factory-refurbished LCD monitor after it died, the very night before this hack-a-day was posted, and ended up taking it to the lab at work, replacing 5 vented electrolytic caps on the logic board (not the inverter caps, those were OK), and now it works great.

    What was really interesting was that I could see that the largest cap on the logic board had already been replaced when it was refurbished – there was even a little tag to mark it. I’d guess it was the same unheard-of brand of cap that I replaced. All of the caps made by (2) other manufacturers were fine. Now that all those POS caps are out of there, I hope we’ll get several years of good service from it.

  18. just some clarifications…

    oscon++. these are great caps. for the record, though, they do have an electrolyte, but it’s a solid electrolyte (compared to the cheapo aluminum electrolytics used).

    not all caps fail short. alum / tantalum / polymer electrolytic caps tend to, but ceramics and others don’t. however, since the big bulk caps are typically electrolytics, you are right that it’s often fair to just check for a short over the cap.

  19. Hi my name is Tony,,,and I want to thank you for your inf about how to
    repair lcd monitor,,,i read your page ,,and you know what,,i fix this
    monitor that I found somebody had put it out as garbage,,,its a
    westinghouse but the parts inside are just like the one you have on
    your pictures I replace the same 2 caps they where bad,,,you could see
    no picture when you put it on,,,and now it looks like new :)

    just one problem,,I have like a very fine red line on the right side of
    the screen from top to bottom is not bad,,,,for been the fist time ever
    me doing electronics repairs,,,maybe when I was soldering the caps I
    put too much heat,,,If anybody could give me an idia why this happen is
    really appreciated ,,thanks again for your inf

  20. I tell everyone with LCD televisions that if theirs fails to call me. I know that manufacturers use cheap-ass capacitors that mostly come from China.

    When I get the PS boards I note the bulging and leaking caps and replace them with good capacitors. Charge em’ parts and a small labor fee and they’re happy.

  21. I am looking for a conductive liquid that connects the electrical contact to the rubber tubes to the lcd screen. As in old lcd screens and not monitors. Any ideas would be appreciated. I used to years ago work at a tv repair place and we used to use a product for this after we cleaned the contact to repair the lcd but for the life of me I can not remember what it was called or was chemically.

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