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CCFL back light problem


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#1 Blufx

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Posted 09 June 2014 - 04:09 PM

I have a Dell Inspiron 1545. When I got it, the screen lit up,but it was smashed. I found a replacement screen, when I turned it on, I saw the LCD get power but then went black. With a flashlight, I could see Windows had loaded. I ordered a new inverter and it did the same thing. Less than a second of backlight then gone. So I ordered a new video data cable and another inverter. It did the same thing again. I pulled the screen and connected the backlight to an HP laptop and the backlight works fine.What is going on here? Why would it keep blowing inverters? Oh, the replacements were genuine Dell, not aftermarket.

Looking back....I should have been a lot more specific when I said I wanted to be somebody.albertavatar.jpg


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#2 zingo156

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Posted 10 June 2014 - 07:40 AM

Was the replacement screen exactly the same as the original? On the back of the lcd panel there are numbers wxga154XXX v1.1 for example, you need to make sure that it is the exact replacement. Dell 1545's were very picky about which lcd panels they worked with. I recall that specific model having issues with certain replacement panels, either not being bright enough or the brightness would not adjust using the keys etc.

 

Make sure that it is the exact replacement lcd panel. Because it is an older computer, you may have to buy a used panel, new will likely be very expensive.

 

It is also possible you got a bad new inverter. Sometimes "new" isn't actually new. The most common causes for lcd panels / backlights to act this way are: incorrect replacement lcd panels, bad cables, bad inverters, possible problem with the main board.


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#3 Blufx

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Posted 10 June 2014 - 09:28 AM

@zingo156,

The display is working as stated in my post, so it's not the 1545's "pickyness". You don't think I got three bad inverters in row, do you?


Looking back....I should have been a lot more specific when I said I wanted to be somebody.albertavatar.jpg


#4 zingo156

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Posted 10 June 2014 - 10:17 AM

The pickyness I encountered was not related to the video signal but rather the backlight and the problem was generally the inability to adjust the brightness correctly or a very dim screen...

 

I doubt you have 3 bad inverters.

 

Since there is an image on the current panel as you describe using a flashlight, I doubt it has anything to do with the lid closing sensor, but it might be worth checking into this. Generally this is a magnetic switch, when the lid is closed the magnets in the bezel shut off the screen. You can open and close the lid a few times in a row to see if any backlight flickering occurs etc. Double check that the magnet in the bezel is still there. Sometimes they fall out when replacing the lcd panel.

 

You have already tried 1 other video cable, I have actually had to order 3 cables in a row for an older computer where only used cables were available to get 1 good cable.

 

Personally I would try a different lcd panel in the 1545 if the current replacement did not match the original panel exactly. I couldn't find a pinout for the 1545 inverter input (motherboard video cable to inverter plug), if you can find it, you can test the voltages that go from the laptop into the inverter, DO NOT test the output of the inverter (inverter plug to lcd panel) unless you have a multimeter that is meant to handle the high voltage the inverter outputs.

 

Generally the inverter input cable pinouts are something similar to this:

 

  • Vin - ~20V
  • Vcnt - 0V to 5V - low = disable, high = enable
  • A-dim - Analogue brightness control - anywhere between 0 and 3.3V - 0V is brightest, 3.3V is darkest
  • P-dim - Pulse Width Modulation brightness control - square wave between 0V and 1.6V
  • GND - 0V ground connection

Edited by zingo156, 10 June 2014 - 10:19 AM.

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#5 Blufx

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Posted 10 June 2014 - 10:23 AM

I'll take all this into consideration. meanwhile, I'm looking into the posiability of the display fuse being blown. I may have been wrong about backlight working for split second. It could have been a change I saw when the display recieved power.


Looking back....I should have been a lot more specific when I said I wanted to be somebody.albertavatar.jpg


#6 zingo156

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Posted 10 June 2014 - 10:26 AM

I assume you have already tried to adjust the brightness up by using the FN key + the brightness keys?


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#7 Blufx

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Posted 10 June 2014 - 10:39 AM

No, I haven't. The reason being, when fully dimmed, the backlight isn't completely out, so I should see the back of the display light up some. But, I just found the display fuse in blown. Looking into replacing it now.


Looking back....I should have been a lot more specific when I said I wanted to be somebody.albertavatar.jpg


#8 zingo156

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Posted 10 June 2014 - 10:42 AM

Did you try testing with the original panel again? IF the backlight still works on the original panel, the cable and mainboard are likely fine. This would indicate a incompatible lcd panel.


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#9 zingo156

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Posted 10 June 2014 - 10:44 AM

I got that last update a bit late. If the fuse is blown this likely is the problem.


Edited by zingo156, 10 June 2014 - 10:44 AM.

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#10 Blufx

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Posted 10 June 2014 - 10:44 AM

The original panel won't work with a blown fuse either. I'll fix the fuse problem first.


Looking back....I should have been a lot more specific when I said I wanted to be somebody.albertavatar.jpg





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