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I am having problems diagnosing the error with a notebook LCD display inverter.

Symptoms: After switching the notebook on, the LCD backlight comes on but the intensity oscillates rapidly (flickers). After about 1 second the backlight turns off completely. Once the backlight has turned off, the AC output of the inverter measured with a DVM is 0 Vac.

I visually checked the inverter board and there are no obvious faults.

Given the symptoms, can anybody venture a guess at the problem?

  • On the one hand I am tempted to say that the backlight is ok (after all it ignites) and the problem is more likely to lie with the inverter.
  • On the other hand I am wondering whether the flickering of the bulb (faulty bulb?) causes a open-circuit protection of the inverter to kick in after 1 second.

So in summary I am not quite sure whether the fault is more likely to lie with the bulb or the inverter.

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Is the backlight a cold cathode fluorescent tube (CCFT)? –  JYelton Jan 2 '13 at 20:26
    
@JYelton I believe so but have not taken everything apart. CCFT is the standard for LCD notebook backlights however, no? –  Arik Raffael Funke Jan 2 '13 at 20:39
    
Repair questions are off-topic. –  Leon Heller Jan 2 '13 at 20:44
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@LeonHeller Point taken. I have remove the repair component from the question and focused on the fault diagnosis procedure to make the question and its answers transferable to other situations with LCD backlight issues. –  Arik Raffael Funke Jan 2 '13 at 20:51
    
@Arik Not necessarily, there's also LED backlights, but they wouldn't require an inverter. –  JYelton Jan 2 '13 at 20:56
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1 Answer

Just be aware that there are potentially very high voltages on board the inverter. Be careful.

It is entirely possible that you'll be able to find a replacement part from another laptop. There are a few common suppliers that multiple manufacturers used. Look to a laptop supply place in your area for leads and supplies. Here I am referring to both the CCFL and the inverter.

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Thanks for the warning about the high voltage. It is one of the reason why my fault-finding efforts were fairly rudimentary. I did not want to fry my DVM... Regarding replacement: Sumida is a very common supplier. My primary concern is that I do not know to what extent voltages and current requirements of backlights in different laptops are comparable. Also, as already mentioned, there is the issue of the 4 IO(?) pins. –  Arik Raffael Funke Jan 2 '13 at 20:43
    
@Arik You may want to look for a similar or exact model laptop with a cracked screen or dead motherboard, and see if you can extract working backlight parts from it. –  JYelton Jan 2 '13 at 20:57
    
@JYelton Good idea, unfortunately it is a rare model (about 1 on Ebay worldwide every few months). Maybe I will get lucky... –  Arik Raffael Funke Jan 2 '13 at 22:53
    
+1 for the suggestion to replacement. It's called fault isolation method in troubleshooting. However this could not be a final accepted answer. Because I mean it's all about symptoms and root cases. –  Standard Sandun Sep 30 '13 at 10:34
    
Most probably this is due to electronic dieseling issue. I'm not aware of this, but electriciantalk.com/f2/… –  Standard Sandun Sep 30 '13 at 10:50
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