Monitor came in with the complaint
of display shutting down after 1 second. You could hardly see any
display/logo because it happens so fast. Most of the LCD Monitors that
have display shutting problem will shut down after few seconds and not in one second.
Once the cover was removed I could see a bulged e-cap. I thought by replacing the e-cap the Monitor will come back alive again but I was wrong. It seems the problem still the same. The only thing I could suspect was the bad backlight and bad high voltage transformer. I did not suspect the Inverter IC because it is usually very robust.
Fortunately customer brought in two similar LCD monitors and I could
swap the boards to see which board is causing the problem. Although I
have the spare backlight, I still prefer to use the same model parts for
comparison purpose. The first thing I do was to swap the working LCD
panel that has 4 good backlights. The outcome stills the same-shut down after 1 second.
Next, I swapped the Inverter/Power board (I/P board) to really make sure is indeed this board is the problem and not the mainboard. It is confirmed that the Inverter/Power board was the problem.
My next move was to swap the high voltage transformer. Although the high voltage transformer checked to be good, I still have to replace it. The reason for it is because some high voltage transformers could breakdown when under load. Even after the replacement of the high voltage transformer, the problem still has not resolved it yet.
The only choice I left is to either direct replace the Inverter IC
(SEM2005) or to check on the ballast capacitors. For your information if
one of the ballast capacitors have problem the display could go into
shutdown mode after powered it On.
I did not check on the ballast caps and instead I opted to replace the inverter IC first. I took out the inverter IC from the working unit and soldered it on the bad power/inverter board. Guess what is the result? The LCD Monitor worked superb!
Now, obviously the IC that I took out should be bad because the bad Monitor already working with a new inverter IC. So I soldered the bad Inverter IC onto the working Monitor power/inverter board and expected that it will shut down in 1 second. I was stunned when the LCD Monitor also worked perfectly!
My conclusion was that I made a mistake that I did not resolder the suspected inverter
IC first. I should have resolder the IC before putting in a working IC.
It was a cold solder joint problem. No worries about this because you
can learn from my mistake. My mistake is your gain.
In the future if you see any LCD Monitor that the display shutdown in 1 second and not in few seconds, then head on to the Inverter IC section. You can:
· Resolder the IC first and if the problem stills the same you can….
· Direct replace the Inverter IC and if the problem stills the same you can….
· Check all the corresponding components related to the Inverter IC
Of course before you do the above tests make sure there are no bad or
bulged e-caps. There is no harm trying to swap the backlights or the high voltage transformer first. The choice is yours. After all troubleshooting should be fun.
Note: Please do not attempt to perform the repair work if you do not know about electrical safety.
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Click here to learn the 10 True Repair Case Histories Of LCD Monitor Volume 1