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LG W2452V 24-Inch Monitor Tear-Down And Repair

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Now That's More Like It

The 24V rail looks considerably better. Ripples are reduced from a wildly fluctuating 600-1000mVPP to a steady 200mVPP, even without super-sizing (and despite the Epcos having a 100kHz impedance of 27mΩ vs. 18mΩ for Samwha).

Out of curiosity, I tried measuring the old 35V caps and neither of my meters were able to take a reading due to excessive leakage current. Those two capacitors were definitely well past their prime.

Standby Power

Both my multimeter and DIY current probe agree that the monitor draws 43mARMS on standy at 117.6VRMS line voltage, yielding an apparent power of 5.5VA. The part of the current waveform that is leading by nearly 90° is the power input EMI filter's capacitors, while the small 150mA bumps are from the input cap getting topped off at AC peaks. Those peaks are enough to reduce the lead to 61° and bring the power factor up to 0.49. The off-scale glitches (about 300mA peak) are runt pulses from the APFC when it initially detects the top-off current.

Once distortion power (everything that is not 60Hz including noise) and reactive power are subtracted, the net standby power is 1.7W.

Turned On

With the display turned on, the APFC controller kicks in and the current waveform tracks the voltage waveform closely whenever the line input is above 50V. The input current is 504mARMS leading by 7° at 117.1VRMS for 59VA with a power factor of 0.99, which is practically perfect.

After removing what little distortion and reactive power is in here, we are left with 57W net power. This is with the monitor on its “no signal” screen and 40% brightness. I wonder how much of a difference my repair might have made, but I did not think of measuring power and PFC before the switch.

To Recap

Replacing caps is just about the simplest and cheapest electronics repair you can possibly perform, next to replacing fuses in an otherwise working circuit (at least when the fuse is not internal and soldered to the PCB, as is the case here).

What really bothers me is how so many consumer electronics manufacturers appear to be using caps that barely outlive the warranty when they could get considerably better ones, preferably not discontinued for the better part of a decade, for a few extra pennies. Things like this make me wish governments would bump the minimum legal warranty to three years to reduce the amount of e-waste generated by what appears to be engineered failure. Aside from the output caps, everything else inside the monitor still looks good as new.

I hope you enjoyed this different tear-down! If you want more, leave suggestions in the comments below.

Topics
LG
Monitors
22 Comments Comment from the forums
  • iam2thecrowe 16 March 2015 07:43
    I normally find in Samsung monitors a Samxon capacitor leaking. I swear monitor manufacturers put them in on purpose as a time-bomb capacitor. They fail after about 5 years, long enough that you thought, ok well i had a good run, but not short enough that it is an early failure. Its good to see an article like this, many monitors can be saved this way if you have a little soldering skill.
    Reply
  • coolkwc 16 March 2015 07:58
    Bad cap again...the cheapest yet effective time bomb of all components. Seldom got ppl want to dismantle dead old monitor even they have solder skill, simply because dismantle process before you can access to that tiny component itself already stopped alot of ppl ambitious. So i say this is effective time bomb to kill the device.
    Reply
  • iam2thecrowe 16 March 2015 08:02
    15491836 said:
    Bad cap again...the cheapest yet effective time bomb of all components. Seldom got ppl want to dismantle dead old monitor even they have solder skill, simply because dismantle process before you can access to that tiny component itself already stopped alot of ppl ambitious. So i say this is effective time bomb to kill the device.

    I generally have no problem getting anything apart and it only takes a few minutes. But yea i agree with this a little, a HP monitor i recently tried to fix was held together with noting but plastic clips, it was not designed to be taken apart once assembled. The plastic clips often break and they don't go back together 100%.
    Reply
  • crmaris 16 March 2015 08:42
    When you want to check which capacitor is preventing a PSU (embedded in a device or a standalone) from starting try heating the ones that look defective with the heating iron. The bad cap once heated will allow the PSU to start and then you will know which one is bad.

    If you want a more scientific way then you should get an ESR meter. I have seen many caps that weren't bulged but still were bad (high ESR).
    Reply
  • coolkwc 16 March 2015 09:44
    Basically none of them except those 'audiophile' equipment and PC component hear about our rant over internet/forum about badcap. Consumer product they often use dirt cheap component to maximize their profit. Nowadays especially those Japanese and Korean brand, they just provide design, and left manufacturing process (material decision) to those China maker, so basically Japanese and Korean device = China brand. A good example is Panasonic product never use a single piece of capacitor from its own brand or any other Japanese brand despite the fact that its capacitor is highly reputable. What a shame.
    Reply
  • Metalliferous 16 March 2015 10:53
    Nice article. How much time did you spend repairing it?
    Reply
  • Daniel Sauvageau 16 March 2015 13:50
    15491955 said:
    If you want a more scientific way then you should get an ESR meter. I have seen many caps that weren't bulged but still were bad (high ESR).
    To use an ESR meter properly, you have to remove the caps from the circuit first and that's half of the replacement job for a cap you are already suspecting might be bad to start with. I went with the "targets of opportunity" strategy there: I'm already elbows-deep into this thing, might as well replace all potential suspects while I am in there instead of discovering a few more years down the road that another one that I skipped decided to go bad.

    If you paid someone $75-100 to repair an LCD, would you risk having to pay for having it repaired again 3-4 years due to skipping a $5 ($1 part + $4 time) opportunistic part replacement?

    As far as the caps from my previous repair in this monitor go, I would be really surprised if they went bad without external signs since Panasonic is a far more reputable capacitor brand and the caps I used have much better specs than Samwha's. I repaired a bunch of PSUs using Panasonic FM-series caps and none of them have as far as I know.

    If I had an ESR/ESL meter, I might have pulled one out just to see how the three years used FMs compare against fresh ones.

    15492329 said:
    Nice article. How much time did you spend repairing it?
    The most difficult part is prying the bezel off to remove the LCD from its enclosure. That part alone took me about an hour the first time since I did not know what sort of snap arrangement was used and there were no broken snaps to give me easier starting points. When I opened it up to do finish the repair this time around, I could have been in and out in about an hour, were it not for the hours spent taking photos for the tear-down.

    The repair itself only takes a few minutes once you have access to the PCB when you have a strong suspect before you even open the device and are going straight for it before investigating anything else.
    Reply
  • cats_Paw 16 March 2015 13:57
    I normally find in Samsung monitors a Samxon capacitor leaking. I swear monitor manufacturers put them in on purpose as a time-bomb capacitor. They fail after about 5 years, long enough that you thought, ok well i had a good run, but not short enough that it is an early failure. Its good to see an article like this, many monitors can be saved this way if you have a little soldering skill.

    Em... yeah its called Planned obsolescence, nothing new, just another way most people are getting F'ed and dont know it.
    Reply
  • razor512 16 March 2015 17:04
    Many monitors now use lower quality capacitors in order to shorten the lives.

    Some will even design the boards around a more difficult repair, for example acer likes to sometimes completely flatten the leads against the PCB before soldering, thus it becomes annoying to desolder.

    Here is the repair I did on my acer x191w a while back https://www.youtube.com/watch?v=hLbSbhvTTgY

    PS, even on some relatively high quality brands, you will often fine a few cheap capacitors used in order to shorten the life of the panel.

    The same also applies to many HDTV's

    If the capacitors do not have the leads completely bent, then you are looking at about 40 seconds to a minute to replace each bad capacitor, if they are bent, then it takes much longer because there is always a little bit of solder left over, and you do not want to pull, even if you see a tiny bit as you do not want to damage the solder pads.

    While the companies know that some people will do a repair them self, they know that the vast majority of people will not want to do the repair them self. Thus using a design that is is centered around being harder to fix, will prevent them from going to a 3rd party repair service, as the work involved will make the repair costs too high to justify it as compared to just getting a new device.
    Reply
  • JayTs 16 March 2015 17:07
    Years ago my Acer monitor died after only 18 months, and I did a repair like this one. I had never opened a flat screen monitor and was amazed at the cheap construction, being held together by wimpy plastic clips and sticky tape. I found failed capacitors and decided to replace all of the caps with high-quality Nichicons. Four years later, the monitor is still working perfectly, running about 16 hours per day.

    For anyone who wants to try this type of repair, you need to know the following specs of each capacitor:

    1. Capacitance (microfarads or uF). Match or exceed the original.
    2. Rated voltage. Match or exceed the original.
    3. Diameter and length. You may use a different size if you are sure it will fit.
    4. Lead spacing. Measure the distance between the leads from the cap or holes in the PCB.
    As explained in the article, capacitors in the power supply should be chosen to handle high ripple current and/or low ESD as necessary.

    Once you have the information, it's complicated but not too difficult to find replacements at Mouser, Digi-Key, or other reputable electronic component distributors. Pick a top brand like Panasonic, Nichicon (my two personal favorites). Look for "Aluminum Electrolytic Capacitors - Leaded" or similar.

    To replace all of the capacitors in my monitor, I spent about $15.

    With good quality capacitors, how long can a monitor last? Who knows?
    Reply