Author Topic: LCD PSU repair  (Read 1959 times)

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Offline Wolvenar

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LCD PSU repair
« on: August 14, 2014, 10:13:10 pm »
After a forum member recently posted his LCD TV failure, I figured I could do this write up, hope it helps.
(oztules, please chip in anything you may find omitted, wrong, or otherwise helpful as you desire)

Sorry images were an afterthought on this project, so not many to show what was done.

I picked this LCD TV up some time back, of course because it did not work.

The problem was the typical power supply capacitor problems that plague many LCD.
This particular supply was designed a bit less than great from the start.

These power supply are built to work over large voltage ranges, and with less than perfect power but these supplies are mean on capacitors given the bad ripple they feed these caps even with the best of power conditions.

This is the TV with the back off, in this set the top module is the power supply.
It should be easy to pick out as in most LCD sets its the one with the big caps, transformers, and likely the largest heat sinks
( FYI this is certainy not true in a plasma set)


In this set there where two caps at fault, it was very easy to pick out the problem as these had swelled and leaked
These where the two black caps near and right of the two yellow transformers. Pictured are the new caps already installed.
Sorry I do not have the images of the originals available at the time I typed this up.


After finding and installing some caps that had somewhat better specs for the circuit, replacing the fuse, and reassembling everything
I had a new ( to me) cheaply obtained television.




This seems a fair walk through for someone with average electronics ability , Im sure there are hundreds of such videos on youtube, maybe even for whatever  model you may be working on..
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline oztules

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Re: LCD PSU repair
« Reply #1 on: August 14, 2014, 11:30:40 pm »
Nice work there Wolv.

I'm a bit miffed it was only the caps.. ;D. I seem to get them with caps and fets and driver problems in the main... a few nice ones like that make it worthwhile. :)

I have found that this is the main problem with modern electronics...... nearly always the supply fails, and because of the isolation afforded by the transformer, it seems that the cancer goes no further... a good thing too..... as most of the down stream stuff is too small to handle  for my old eyes...... that .........and I would not have a clue how or what half the stuff does.... :o



.................oztules
Flinders Island...... Australia

Offline Wolvenar

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Re: LCD PSU repair
« Reply #2 on: August 15, 2014, 12:08:21 am »
Don't feel to bad, today I was going to prove a point to my son and, well came up on the short end.
He was giving me flack about my eyesight when I complained about a board and the  (perceived) near dust sized components I was soldering to.

So I dug out a roasted old computer mainboard with similar components on the backside. took high rez pics, and counted the parts.
I vacuumed the garage floor, which part of near the workbench is covered in bedliner for traction.
Then took the heat gun out and heated up the mainboard and a few taps later, solder and a bunch of electronic parts and a bunch of once liquefied and splattered solder are all over that rough bedliner.
I figured, this kid is supposed to wear glasses, but adamantly refuses to do so.
With mine on I have 20/05 vision. *I'll show HIM*.

Dared him to get all the components and count them.
I figured there was NO way he would see ALL the parts and get them picked up out of the splattered solder and other garbage stuff on that rough floor.

Guess who was showed a thing or two. Though he did concede to understanding why I complain after that.

Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline MadScientist267

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Re: LCD PSU repair
« Reply #3 on: August 15, 2014, 09:30:11 pm »
Done a few of these myself as well... most of them caps as culprits...

One thing I usually do in addition to replacing the caps is add some 0.1uF Mylars across each one if you can squeeze them in there, since there's usually only a few of them anyway. Between cheap caps, stolen formulas, and skimping on count, they're a bullseye for the cause of the current failure and the next one as well. Taking the sharpest spikes away from them seems to help greatly... they run cooler and subsequently last longer.

Seems to help out on any SMPS, but it appears that LCD monitors/TVs in particular got a really cut off stick.

Steve
Wanted: Schrödinger's cat, dead and alive.