Why my LCD monitor backlight turns off?

Question

As long as I used my VGA cable, my LCD monitor worked fine. But when I switched to my DVI cable, sometimes my monitor turns off. When it happens the power light still on, the screen is dark but the very darkened images can be seen in certain angles in certain circumstances, so I supposed that just the backlight has turned off. I presume it's the cable or the connectors fault, but I am asking here if you had a similar experience, and if the only solution is to buy a new cable.

My monitor has both connections (VGA and DVI) but my video card has only DVI. So when I used the VGA cable I used with an adapter between it and the video card.

** UPDATE ** It wasn't the cable. I switched back to my old VGA cable and it is still with problems.

Answer 1

Looking for picture behind dark screen

If you can see picture even while backlights are not working then problem almost certainly lies in monitor powersupply/inverter board.

Sometimes it will be extremely hard to see picture when backlights are gone. You should try external lighting at different angles and at different luminosity. If possible, it could help if there is fullscreen animation running while checking this, for example cartoons with great contrast and bright colors.

Causes of darkness

Blown/leaking/dry capacitors are very common problem with flat screens, they are also pretty easy to check for defects (most of time visual inspection is all you need).

Capacitors are also relatively cheap and pretty easy to replace (if you know how to use soldering iron), just remember to check orientation for +/- leads (likely marked on board). However you should also inspect those high voltage cables for burn marks, especially near cold cathode tubes (not found from screens with LED backlights).

More on topic

• On laptops, there's small inverter board located just under screen frame casing (in most models) that is often cause of black screen. These could be very cheap for some models.
• See PSU failing or Mainboard failing? for picture of defective capacitors.
• There's also simple power cord test that you might want to carry out:

  Pressing power button (pulling plug out for few seconds) many times also speaks toward broken PSU case as when you press and release button it will discharge capasitors and then immediately charge them again, doing this many times could still make almost broken capasitor to work once again for some moments.

Answer 2

Are you sure there is no setting in your OS that controls backlight? If Vista/7, try checking the powersaving feature to make sure nothing is dimming backlight.

EDIT: So, no use. If your PC came with a DVI/VGA adapter, try it on the faulty DVI port. That way, you can rule out DVI Connector (if it works well) or DVI cable (if it doesn't).

If everything else fails, try borrowing a cable from a friend, or get a really cheap one, that at least works. If it was the cable, you can later buy a higher quality one.

This way you rule can out the most expensive parts of the issue, the monitor or the video card.