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/