Troubleshooting And Repairing BENQ LCD Monitor (With Video)
In my very small workshop, one corner is assigned as my office space. A bench with a desktop computer serves my needs as well as a wall mounted monitor. The BENQ monitor had been working for some time and when I decided to upgrade my computer, perhaps it felt intimidated and decided to start to falter.
The main issue that was happening was that it would work and then the screen would go black. But before I started to suspect power supply issues a simple fact caught my eye – the green power light was on, indicating that the computer was not asleep, which would give the monitor an orange light.
So what was the next step?
The workshop lights were turned out and a torch was shone onto the screen. Why do that? In these monitors, a backlight is used to illuminate the display. Without it, the screen becomes almost unreadable. A simple trick is use a torch in a darkened room, allowing the display to be seen. That’s what I did in this case.
What did I see?
The little character I use on my YouTube channel could just be seen, showing that the monitor was operating, but the backlight had failed somehow. The main issue was that this was an inconsistent fault, so time would have to pass before it raised its ugly head!
So into the lab it goes!
Removal of the back cover was easy after the screws and the stand were removed. Gently levering the clips allowed the cover to be removed. The VGA anchor screws/nuts needed to be removed so that the metal cover could be slid out of place.
Next, the fun part – a good visual!
All the capacitors had their heads intact, however they would be shortly checked for excessive ESR.
Then I did one of the most important steps in a diagnostic path. I took a long, hard look at the circuit board. It was time well spent.
Two of the transformer pins had cold solder joints. But of course, diagnosis didn’t finish there. As mentioned, all capacitors were checked with the Blue ESR meter.
Two of the capacitors were around 3 times their suggested resistance.
Just for the fun of it, I tested the new capacitor ratings against the faulty ones. Both clearly showed the difference.
The capacitors were installed in place, with careful attention being paid to their polarity. I soldered the 2 joints on the transformer that had failed, but, looking back, I should have soldered all the transformer joints to make sure that this doesn’t happen again in the future.
I finally cleaned up the areas with Isopropyl alcohol, which removed flux impurities.
The monitor was ready to reassemble, but I wanted to run it partially disassembled for some time. I placed a sign on the monitor so that both myself and others were aware that it was a possible hazard.
I was happy to reassemble it after 5 hours of testing, confident that the solution had been found.
If you are interested in this repair, you can see a video on my channel following the link below:
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article below: https://jestineyong.com/biolight-3000-repair/
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Albert van Bemmelen
May 12, 2020 at 7:42 pm
I was given a bad Samsung T200 monitor that also quits showing any screen but always exactly after about 1 second after it was switched on. I already looked for cold solderjoints and other visible signs but couldn't find anything wrong thusfar. Maybe it is just as easy as replacing the bad e-caps on the mainboard if it is a bad ESR problem. But I'm afraid that it never is that easy, so I have put the LCD monitor aside for another time. And fixing without a service manual doesn't really help.
Mark
May 12, 2020 at 9:37 pm
Hey Albert,
I had used another monitor for quite some time as this one played up, but when the other one failed (I am still repairing this) I had to bring out this BENQ monitor. The caps on this one were quite bad and together with the cold solder joints, I scored a win.
Fortunately, it has continued to faithfully work. I hope this is a long term solution.
Alexan Catalin
May 14, 2020 at 4:16 am
Hi Albert,
Try to look at a backlight transformers, when switch on. One of them is in shortcircuit, internally. And is very heated.
Parasuraman S
May 12, 2020 at 8:48 pm
Highly professional and thorough approach, exposing the quality of service. Well done! The sign board is really a marvelous idea, which normally only a few would think of! You are great! Many thanks for sharing!
Mark
May 12, 2020 at 9:39 pm
Thanks Parasuraman for your kind comments.
Over the years I have been shocked many times and fortunately survived to tell the tale.
I don't want to put myself or others at risk, so I think a simple sign is a simple solution to keeping everyone safe.
Albert van Bemmelen
May 12, 2020 at 11:39 pm
I hope all can read Mark (lol).
Lynn Blakely
May 12, 2020 at 11:50 pm
Another complete discovery of bad caps and bad solder joints. Good job Mark. I have four LCD monitors, and one active amplified speaker to repair I am retired and have other duties that require quite a bit of my time. I do like the ESR meter that you and a lot of others have, I built mine from a kit. Thanks for your nice write-up, and pictures.
Mark
May 13, 2020 at 7:54 am
Hey Lynn,
Time is the main killer. My day jobs keep me very busy & I look forward to doing an electronic repair. As a hobbyist, each repair I do, I gain confidence and skills to attempt the next repair. I must admit, not all are successful 🙂
Waleed Rishmawi
May 13, 2020 at 6:51 pm
great repair job. I like the sign idea. thanks for sharing. have a blessed day
Mark
May 15, 2020 at 7:05 am
Thanks Waleed,
I just feel a lot safer having that reminder 🙂
Gassan Ali
May 14, 2020 at 5:46 pm
The Blue ESR meter doesn't require the caps to be removed from the board. Great!
Amos Miganda
May 14, 2020 at 10:22 pm
Good work
Mark
May 20, 2020 at 8:47 am
Thanks Amos
Mark
May 15, 2020 at 7:07 am
Yes it is a great meter - saves lots of time 🙂
Humberto
May 18, 2020 at 9:45 am
Well-done, Mark
Mark
May 20, 2020 at 8:47 am
Thanks Humberto
Adrian
May 19, 2020 at 9:31 am
Good Job Mark
Mark
May 20, 2020 at 8:48 am
Thanks Adrian
Joven Urbano
June 30, 2020 at 5:11 pm
I noticed you were testing capacitor's ESR in-circuit. Is this accurate? Thanks a lot for your reply.
nishshanka
March 19, 2023 at 3:59 pm
thanks sir -I am try now connect after