Author Topic: Anybody know anything about Monitors?  (Read 4575 times)

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Offline Fishplate42

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Anybody know anything about Monitors?
« on: June 09, 2012, 12:12:40 pm »
Hi folks,

Following Dave's example I have just torn down an LG L1953S monitor that just stopped working. Managed to get inside (without any Percussive Maintenance!) expecting to find a fuse gone or something of that nature. It all looks fine, no burnt components etc.

On the bench, I noticed that as the the mains power is connected the power indicator LED lights for a few seconds then goes out as if it has powered down. The monitor is completely non responsive after that.

This is one of a matched pair so I have two options, either dump it and buy a couple of new ones or try and find out what is wrong with this one. It was fine yesterday but this morning it would not power up. The monitor is about 4 years old.

Any suggestions or help would be appreciated. 

Thanks,
Ralph  :(
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Offline GeoffS

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Re: Anybody know anything about Monitors?
« Reply #1 on: June 09, 2012, 12:16:36 pm »
Do you have the service manual for the monitor?
There's usual some common fault troubleshooting in them, at least LG ones.
 

Offline NiHaoMike

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Re: Anybody know anything about Monitors?
« Reply #2 on: June 09, 2012, 12:56:24 pm »
Check the voltages from the power supply board. A common fault is bad capacitors.
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Online mikeselectricstuff

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Re: Anybody know anything about Monitors?
« Reply #3 on: June 09, 2012, 01:19:54 pm »
As it is a pair you may be able to do some board-level swapping to narrow things down.
Bad PSU caps are a common problem but LED coming on could mean the PSU may be OK but it is deciding to turn off due to some more subtle reason.
See if you have what looks like a plausible voltahe (typically 3.3v) across decoupling caps on the main logic board.
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Online SeanB

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Re: Anybody know anything about Monitors?
« Reply #4 on: June 09, 2012, 01:48:46 pm »
As well as bad capacitors check with a strong light if there is anything displayed on the LCD, as often the lamp will be shut off by the protection system if it is too worn out. This takes a few seconds to decide if it is going to run the tube before it shuts down. On the inverter panel there will be a capacitor for startup that can be shorted out to run the tubes to check that this is the fault. You will need to RTFM for that, and most of the manuals available online free will have a rather risqué watermarking on them.

For the manual try eserviceinfo.com as a start, they have a lot of these manuals.
 

Offline Fishplate42

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Re: Anybody know anything about Monitors?
« Reply #5 on: June 09, 2012, 02:20:45 pm »
My, That was quick!

Thank you for the help. I have managed to download the manual and it has a very good Yes/No fault finder in the back plus all the information I will need to have a go at first identifying what's wrong and then having a go at fixing it. I am off on holiday for the next couple of weeks so I will have a go at it when I get back and let you know how I get on.

Thanks again to all of you for the help.

Ralph :)
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Offline Psi

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Re: Anybody know anything about Monitors?
« Reply #6 on: June 09, 2012, 02:45:42 pm »
I have a 24" LG lcd that would power on for a while, then maybe 10minutes later switch off for no reason.
If you pressed the power button again the led would light up and go out a second later.
After you let it cool down it would be fine again for ~10minutes

Managed to track down the problem.

I had assumed it was the powersupply board but after removing and testing it under load for an hour i started looking at the main board.
Managed to track the problem to the reset line on the processor.

There is a small TO-92 package next to the main processor. It looks like a transistor but it's actually a voltage detector with logic output. It's used to hold the micro in reset state until the voltage level has stabilized.
This one had become faulty and as it got hot the output would start to drift all over the place causing the processor to reset.

Its already been unsoldered in this pic, but i added the arrow to show where it was


« Last Edit: June 09, 2012, 02:47:22 pm by Psi »
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Offline SgtRock

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Re: Anybody know anything about Monitors?
« Reply #7 on: June 12, 2012, 06:22:49 am »
Dear Fishplate42:

--I am betting on bad caps. This is where it is a good idea to ignore the "just replace all of the caps, willy nilly" advice and, get a hold of an ESR meter. The board switching tip is a very good one, provided you use some caution. Also, since the power supply is on all the time, you can check it for output, without turning on the unit. For an additional perspective, check the below link, where they are more bodgers than boffins.

http://www.badcaps.net/forum/showthread.php?t=20026&highlight=LG+L1953S

--Please be sure to post some pictures if you can, and tell us of any progress.

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« Last Edit: June 12, 2012, 06:57:36 am by SgtRock »
 

Offline kripton2035

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Re: Anybody know anything about Monitors?
« Reply #8 on: June 12, 2012, 06:39:16 am »
to choose an esr meter (free or buy one) dont forget to visit : http://kripton2035.free.fr/esr-repository.html

also an interesting link all these monitors fail the same way ...
http://www.jestineyong.com/?p=534

good luck

Offline retiredcaps

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Re: Anybody know anything about Monitors?
« Reply #9 on: June 12, 2012, 07:13:53 am »
This is where it is a good idea to ignore the "just replace all of the caps, willy nilly" advice and, get a hold of an ESR meter.

Over at badcaps.net where I'm a regular, one of the reasons we (the regulars) recommend replacing all the caps (when warranted with hard evidence or diagnosis) is that is many of the people who ask for advice are one time DIY fixers/newbies.  For them to build an ESR meter is orders of magnitude beyond their level of expertise.  For them to buy an ESR meter which costs $65 or more, it is cheaper to replace all the caps ($10 or less).

Let me be clear.  We NEVER recommend BLINDLY blanket recapping.

On the flip side, if you are good at building circuits/breadboards and will be fixing many monitors/TVs or "serious" hobbyist/professional, then YES, get or build an ESR meter and do the job properly.

PS. Just because it is called badcaps.net doesn't mean we see everything as capacitor related.  We have helped people troubleshoot and diagnose many bad resistors, voltage regulators, ccfls, smps ics, etc in all sorts of electronic items.

Quote
For an additional perspective, check the below link, where they are more bodgers than boffins.
http://www.badcaps.net/forum/showthread.php?t=20026&highlight=LG+L1953S

I'm not quite sure what the term "bodgers than boffins" mean.  ???  Praise or Put down?
 

Offline kripton2035

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Re: Anybody know anything about Monitors?
« Reply #10 on: June 12, 2012, 10:21:02 am »
problem to me is that these one time DIY fixers often dont have a proper soldier - desoldier station to remove the caps in place properly ..
and in a motherboard with 4 or more layers it can be very hard to remove the caps without burning the pcb ...

Offline SgtRock

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Re: Anybody know anything about Monitors?
« Reply #11 on: June 12, 2012, 10:27:35 am »
Dear Retiredcaps:

--Please allow me to say that I meant no criticism, implied or otherwise, regarding either yourself or your estimable forum.  I had no idea you were a member here as well, and I am glad that you are. I have read hundreds of your posts, and I have yet to see you give any bad advice. I have seen you, however, spend literally hundreds and hundreds (maybe even thousands) of hours patiently coaching neophytes, like myself, in trouble shooting, TVs, Monitors, Laptops, and what have you. Without a doubt, BadCaps and EEVBlog are the finest electronic websites in the World, par excellence, bar none. Trust me, I have seen them all. If either you or Dave Jones says something, it can be taken to the bank. I think that calling yourself a mere "regular" may somewhat understate your importance to the forum.

--The reason I warned against replacing caps willy nilly, is because, there is a lot of that kind of advice out there, particularly on YouTube. With modern multilayer boards, there are a number of ways to screw up when desoldering, and re-soldering. I have learned this the hard way. If someone wanted to learn about non-destructive desoldering and soldering, I heartily recommend that they read all of the pertinent advice at BadCaps. I also highly recommend the Pace series of soldering videos. In any case, I agree that you never blindly advocate wholesale replacement of caps.

--Now with regard to Bodgers and Boffins; Bodgers, were originally wood workers (pole lathe turners specifically). By the time of Bletchley Park they were considered repairmen or maintenance men. This is the sense in which I use the term. Lately there is a negative connotation beginning to be attached to the word through misunderstanding. I shall explain. When Dave Jones takes the cover off of a piece of equipment from a commercial production run and finds wires and components tacked on in a haphazard manner, he refers to it as bodge job, or a bodge component, meaning slipshod or jake leg. However, the same repair job done as a "one off" by a DIYer, who could not easily manufacture a new board, might be the work of a near genius. When DJ could not easily get a replacement switch for his son's electronic piano, he simply drilled a hole and bodgered a different switch into place, and Dave is no Jake Leg. The same could be said for my bodge wire repair to my friend's Garmin Street Pilot (see attached picture) after Joelby of EEVBlog was kind enough to examine my brilliant photograph.

--Now, Boffins, strictly speaking are Scientists, but Engineers, particularly Electrical Engineers can be so advanced as to be indistinguishable from Boffins (My apologies to Arthur C. Clarke).

--To put it simply, although the two sites overlap, and have many members in common, I would say that BadCaps is more concerned with repair and the philosophy of repair, and that EEVBlog is more concerned with design and the philosophy of design.

--I hope that clears up any unfortunate understanding that I may have inadvertently engendered.

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Best Regards
Clear Ether
« Last Edit: June 13, 2012, 06:46:39 pm by SgtRock »
 

Offline Psi

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Re: Anybody know anything about Monitors?
« Reply #12 on: June 12, 2012, 01:42:48 pm »
The easiest way i found to replace caps on a motherboard is

1) Use a large chisel tip that can touch both cap legs at the same time, add some solder, apply heat to both legs and with a little pressure gently pull out the bad cap.
2) Use a solder sucker to remove solder form the hole which is not the ground or power plane. (one hole will be much easier to get solder out of than the other)
3) Cut the new capacitor legs so the longest leg is the one that needs to go into the cleaned/empty pcb hole.
4) Put the new capacitor in up until the other leg now touches the uncleaned hole
5) Apply the iron to the uncleaned hole and the cap will slide in the rest of the way.
6) Apply and remove solder to both legs to clean up and make a nice join.

Anyone else use that method?
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Offline GeoffS

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Re: Anybody know anything about Monitors?
« Reply #13 on: June 13, 2012, 12:46:31 am »

--Now, Boffins, strictly speaking are Scientists, but Engineers, particularly Electrical Engineers can be so advanced as to be indistinguishable from Boffins (My apologies to Issac Asimov).

Best Regards
Clear Ether

Apologies to Arthur C Clarke I think  :)
 

Offline SgtRock

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Re: Anybody know anything about Monitors?
« Reply #14 on: June 13, 2012, 06:45:21 pm »
Dear GeoffS:

--Indeed, Sir, you are correct, Sir. It was Arthur C. Clarke 1917 - 2008 who said "Any sufficiently advanced technology is indistinguishable from magic.", and not Issac Asimov. My apologies. I am correcting the post.

--I remember reading "Profiles of the Future" in 1966, wherein Mr. Clarke predicted that your TV, Radio, Telephone and Newspaper would all be one device, sitting on your desk. I also remember him predicting that the computing power of Univac could eventually be put in a match box, he was a trifle under optimistic in that case.

--The World owes a great debt of gratitude to men like Asimov, Clarke and Sagan, for getting young people interested in the Sciences.

"When people thought the Earth was flat, they were wrong. When people thought the Earth was spherical they were wrong. But if you think that thinking the Earth is spherical is just as wrong as thinking the Earth is flat, then your view is wronger than both of them put together."
Isaac Asimov 1920 - 1992

Best Regards
Clear Ether
 

Offline baljemmett

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Re: Anybody know anything about Monitors?
« Reply #15 on: June 13, 2012, 07:14:59 pm »
--I remember reading "Profiles of the Future" in 1966, wherein Mr. Clarke predicted that your TV, Radio, Telephone and Newspaper would all be one device, sitting on your desk. I also remember him predicting that the computing power of Univac could eventually be put in a match box, he was a trifle under optimistic in that case.

I believe it was Clarke who had one of his characters, a journalist, typing up copy during a space flight -- on a typewriter...
 


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