Author Topic: Laptop Backlight  (Read 3593 times)

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Offline tazelikechickn

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Laptop Backlight
« on: January 30, 2015, 11:35:36 am »
Hey Guys,

I am working on a HP Compaq Presario V6500 laptop for a friend. It appears to have a backlight issue. You can boot up the laptop, but only see a very slight image when you shine a torch against the screen.

The research I have done seems to indicate either a backlight or an inverter. What sort of voltage feeds the LCD backlight? Can I just feed a certain voltage into the globe turn it on for diagnostic purposes. And what voltage would I be looking for at the inverter output.

Would anyone know where generic backlights and inverters can be purchased in Australia or cheaply overseas?

Any help would be appreciated.

Cheers

 

Offline han

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Re: Laptop Backlight
« Reply #1 on: January 30, 2015, 11:54:59 am »
i replace my Monitor backlight from aliexpress.


just example :
http://www.aliexpress.com/item/530mm-Adjustable-brightness-led-backlight-strip-kit-Update-24inch-lcd-monitor-to-led-bakclight/1176143042.html


there is lot a variant. just search

 

Offline Balaur

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Re: Laptop Backlight
« Reply #2 on: January 30, 2015, 11:57:06 am »
Been there, done that.

DISCLAIMER: PLEASE BE CAREFUL. THE OUTPUT VOLTAGE CAN REACH PEAKS OF 1500 V.

As you said, probable causes are the CCFL or an inverter issue; however I would also have a quick look on the connections and the inverter supply voltage. Just to be sure, I would also try to validate if the On/Off and the brightness signals are at sane values.

Otherwise, I would test the inverter with a spare lamp, if available. If not, I would use a standard CFL bulb, removing his supply and connecting the CFL lamp wires to the laptop's inverter.

Most likely, the laptop CCFL is burnt out. Measure the length and diameter and order a compatible one on eBay. I was always able to find something close to me, but I'm not sure on the situation in AU.

PS: Keep the old CCFL's connectors to refit them to the new one.

However, please note that this is the way I would proceed; this message is not a recommendation or a how to. Take care when experimenting.
 

Offline Flenser

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Re: Laptop Backlight
« Reply #3 on: January 30, 2015, 01:51:55 pm »
I had the same issue.

My approach was to buy one of these CCFL Inverter Lamp Testers. Only US$5 and I get to keep it as a testing tool for the future.
http://www.ebay.com.au/itm/12-24V-CCFL-Inverter-Lamp-Tester-LCD-TV-Laptop-Screen-Repair-Backlight-Lamp-Test-/200985891101?pt=LH_DefaultDomain_0&hash=item2ecbb1511d

This allowed me to test the CCFL lamp in my laptop, which was OK. So I took the risk and bought a replacement inverter off ebay and I had a win, replacing the inverter fixed my laptop screen.
 

Offline Yago

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Re: Laptop Backlight
« Reply #4 on: January 30, 2015, 01:59:57 pm »
Done quite a lot of these, nearly always was an inverter fault.
Ebay is the a good place, the model number and manufacturer will be printed on the inverter.
Got many from this chap too:
http://www.laptoppowerjacks.co.uk/

Depending on the age of the laptop, might also be an LED backlight.
Often simply the flex comes disconnected from the backlight!
 

Offline tazelikechickn

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Re: Laptop Backlight
« Reply #5 on: January 31, 2015, 02:15:55 am »
Thanks for all your suggestions guys. I will look into a tester and see what is available. Also thanks for the links to parts.

Cheers
 

Offline wn1fju

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Re: Laptop Backlight
« Reply #6 on: January 31, 2015, 02:40:33 am »
I replaced both the inverter and the lamp on a Dell laptop because the parts were fairly inexpensive.  But there must be a trick that I don't know, because I had a terrible time installing and aligning the lamp so that the illumination was even.  I never did get it anywhere near factory new.  I'm sure the manufacturing process has a jig and/or tool that drops the lamp in just right.  But mine ended up with a couple of hot spots on the display.  Usable, but not very good.  So be careful!
 

Offline han

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Re: Laptop Backlight
« Reply #7 on: January 31, 2015, 07:32:38 am »
Why not replace with LED baklight?, NO HV, just remove old ccfl and inverter, and find the LED strip suitable with the dimmer controler with the right size.
 

Offline tazelikechickn

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Re: Laptop Backlight
« Reply #8 on: February 21, 2015, 11:51:17 am »
Hey Guys,
It has been a while since I have had a look at this laptop.

I ended up getting a test inverter from Ebay. No light. I also read a trick to check for frequency at the output. By just putting my oscilloscope leads near one another (about 10mm) and then placing them near the inverter output, you get a frequency reading that can be measured. I could repeat this measurement by turning the power off and on with my test inverter. I could see that this inverter was working - but no light showed on the screen.

However I also did this trick with the laptop inverter and no frequency was shown. In my opinion, this shows that both the inverter and also the backlight need replacement.

But that being said, I would like to check the voltages going into the inverter. Does anyone know what these voltages would be (I am assuming it would be around the 12VDC range) and also which pins they would be? I can't see any writing to indicate the correct terminals.

Thanks in advance for your help.
 

Online wraper

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Re: Laptop Backlight
« Reply #9 on: February 21, 2015, 01:34:55 pm »
However I also did this trick with the laptop inverter and no frequency was shown. In my opinion, this shows that both the inverter and also the backlight need replacement.

But that being said, I would like to check the voltages going into the inverter. Does anyone know what these voltages would be (I am assuming it would be around the 12VDC range) and also which pins they would be? I can't see any writing to indicate the correct terminals.

Inverter will shut down in less than a second if there is no load or fauty lamp attached to it's output.
 

Offline tazelikechickn

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Re: Laptop Backlight
« Reply #10 on: February 22, 2015, 04:57:55 am »
Does that mean that the test inverter is set up differently? I had no trouble checking the frequency without any load. Is the inverter controlled by the motherboard and is there a way to test voltages going into inverter on the supply side?
 


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