Inverter or Backlight?

[ShadowReaper]

Hello,

a friend of mine dropped his laptop and he has a problem with the screen. It appears to function normally except that it's very very dark...

I tried the tv-out and it functions properly, so the problem is either the inverter or the Backlight.
Since I do not have a spare Backlight to test it, is there any other way to find
which of the two malfunctions?

Thank you

[PCBONEZ]

Re: Inverter or Backlight?

Step 1:
Locate brightness control and see if it changes anything.
The fall may have inadvertently adjusted it.

If that isn't it then it's hard to say which is bad without taking it apart.
-
An inverter circuit board is less likely to be damaged by a drop than a glass tube.

The screen may have more than one tube and only one tube is out.

Might also be that a brightness control wire to the inverter came loose although I don't know if that method is used in this particular laptop.
.

[Mad_Professor]

Re: Inverter or Backlight?

I would say inverter cable came loose. I had acouple of HP laptops do this, since they forget to put a little sticky tape to hold the cable in place.

[ShadowReaper]

Re: Inverter or Backlight?

I wouldn't say that the cable came loose... I opened it and checked it.
By brightness control you mean the software?

[PCBONEZ]

Re: Inverter or Backlight?

No I mean the IC chip that is operated either by a switch, a combination of switches, and/or some software.
.
Some laptops have the chip in the chassis with wire[s] running to the inverter in the lid.
With others it's built right into the inverter.
.

[kb48]

Re: Inverter or Backlight?

99% of time it is the inverter, due to usually liquid spill or just the transformer or ceramic/polymer caps die on the inverter.

Simple test, take and unplug the FL lamp from the inverter, take a clip lead ground it to the notebook hinge, and turn on notebook. Carefully bring the other end of cliplead near the plug of the FL lamp (white or pink wires). and if it draws a spark or arc then inverter ok. Have to do this when first turned on, as the inverter will just shutdown otherwise.

Using meter carefully proble the other plug, to verify it is getting voltage, usuallyu 5V and also usually 9 or 12 volts. There are also PICO microfuses on the inverter, that may be open. They are white surface mount devices.

IF the FL tube has aged out, or cracked then you would also get same symptoms.
If cracked it may arc over from the inverter board to ground. The FL tubes last a long time, but if either goes bad, the inverter is designed to shut down.

For may HP newer laptops these are very reasonably priced, at $40 or less, I got one for an HP for only $17.50 with free shipping.
Don't try to fix the inverter that is a waste of time.
Too delicate to repair.
Also if the transformer goes bad, it can burn a hole in it as well.

[kb48]

Re: Inverter or Backlight?

Also something simple to check but make sure the lid switch is not stuck. I had this on an older notebook, to cause backlight to shut off. Usually t will also cause system to enter standby mode as well.