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Dan
Dan, Master Electronic Technician
Category: Consumer Electronics
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Experience:  Over 40 years experience in the service and repair of all types of electronic equipment.
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Replaced defective laptop screen (LED backlight LCD). New

Customer Question

Replaced defective laptop screen (LED backlight LCD). New screen is black so is old screen, how do I turn on the backlight, computer is working (hooked to external display). There is only one connector to new/old screen (small ribbon cable). Help please.
Submitted: 3 years ago.
Category: Consumer Electronics
Expert:  Camille-Mod replied 3 years ago.

Hi, I'm Camille, a moderator here on Just Answer. I am actively looking for an Expert to assist you with your question and I appreciate your patience. You will receive an email notification when an Expert replies to you. Thank you again for your continued patience.

Customer: replied 3 years ago.

Thank you Camille for the update, keep me posted. I'm on-call tomorrow (er today) so may not respond to ? or results immediately.

 

Dave

Expert:  Camille-Mod replied 3 years ago.
Thank you Dave, will do:-)
Expert:  hongkongpom replied 3 years ago.

With the laptop on, if you point a bright flash light at the screen can you see a picture where the beam strikes the screen? (or hold the laptop in the sunlight)

 

If so, then it seems the inverter is not working/connected properly or may have malfunctioned if you do have all the cables connected back correctly.

Customer: replied 3 years ago.

The answer that you suggest, ie shinning a light at the screen does work and the screen is displaying a picture.

 

The problem is its an LED backlight not CCFL and I cannot find any information or data related to an "inverter" for an LED. Do LED Backlight require "inverters", if so why/how is there no information listed for possible replacement.

 

For CCFL (which I've replaced before) there are both additional connections and a list of separate parts.

 

I need more help, sorry.

Expert:  hongkongpom replied 3 years ago.

Hello there,

 

Sorry, I missed the part that it's a LED. Yes you're correct that this doesn't require an inverter.

 

Things that come to mind is all the cables are correct & undamaged, then the problem could be to do with the latch switch in the lid, a setting on the laptop which turns off the backlight or damage to the motherboard itself or faulty screen.

 

Is this an exact replacement please?

Customer: replied 3 years ago.

Hello,

 

It is an exact replacement LCD - LTN140AT08. No apparent cable damage, it only has one tiny 2-3 cm connector at bottom of LCD.

 

Laptop has a separate on/off switch for screen and by doing your light trick, have verified it is on. I do not see any other connectors either in the hinges or ??? It does seem to have small wire extending from the connector all the way around the screen and returning to the hinge area but no connections are visible. I've also noted that the covering bezel has a small (~1cm) metal plate (w/blue vertical line) ~ 1/4 distance from the right upper corner. I have thought this might be a magnetic and/or ground, but even w/the bezel snapped back into place, I have no "backlight".

 

Expert:  hongkongpom replied 3 years ago.

Thankyou

 

That wire is probably the wireless antenna.

 

If you put the old screen back in does the backlight come on?

If so then it seems the new screen is defective as that will also prove the ribbon cable is ok.

Customer: replied 3 years ago.

Sorry, I mentioned that much earlier in the original post. Original screen was re-installed and it too has no backlight. It did work albeit minus ~ 2 inches from the left side, but now nada same as new screen.

 

That would point to another part failure, but I've had no luck in finding anything else. I thought your idea about a hinge switch was possible, but it should light up on re-boot and I get absolutely nothing.

 

Dave

 

PS - I noted that I would be at hospital all day, sorry for the delayed response.

Customer: replied 3 years ago.
Relist: Other.
Hi Camile or Hongkongpom - I'm really no closer to my answer than I was on Sunday or have been for the past week. If anyone else has a suggestion, I am open to try, but otherwise this has not solved my problem.

To briefly reiterate:

a) Failed but partially working laptop screen
b) Exact replacement (duplicate) screen obtained
c) No backlight (LED not CCFL) on new screen - old screen placed back into laptop w/same problem. Outside lighting (flashlight etc.) indicates that both screens have/receive data and function - Laptop outputs to external monitor.
d) One connection to screen from laptop not broken.
e) No "inverter" but what prevents "BACKLIGHT"?
Expert:  Dan replied 3 years ago.
Greetings, can you recheck your model number? Am I correct in stating that although the old screen had a defect on the left side you still had a backlight? Only after the changeover did the backlight stop functioning?

Dan
Customer: replied 3 years ago.

Dan you are correct, prior to the exchange, the old LCD worked (backlight and all) minus ~ 2 inches on the left side (reason for replacement). Sony Laptop VPC CW13FX.

 

Dave

 

PS - Off to hospital now, sorry if I don't get back to you until this evening.

 

Expert:  hongkongpom replied 3 years ago.
I'm very sorry but I am out of ideas and will opt out so that other experts can help you with your question.
Customer: replied 3 years ago.

Dan you are correct, prior to the exchange, the old LCD worked (backlight and all) minus ~ 2 inches on the left side (reason for replacement). Sony Laptop VPC CW13FX.

 

Dave

 

PS - Off to hospital now, sorry if I don't get back to you until this evening.

 

Expert:  Paul E replied 3 years ago.
Hi. I have been repairing laptops for many years and from all the symptoms you have described above, the only feasible answer is that the new screen is defective. If your old screen still has the same problem, i.e. that the screen tights up but misses the last 2 inches, then the cable and the LED control circuitry on your main board must be OK. I would suggest contacting the company you purchased the screen from and asking for a replacement. The only other way of testing the new screen would be to install it in another Sony laptop.
Expert:  Dan replied 3 years ago.
Please ignore the prior response.

Experts overposting please read ALL the comments before answering. The backlight does NOT work at all whether the old screen is in place OR the new one. The backlight failed to operate AFTER the new screen was connected and then the old one was tried as well and still did not work.

The concern obviously at this point is what might have been damaged in the changeover or not properly connected.

Dan
Customer: replied 3 years ago.

Hi Dan, Paul, Camile, Hongkongpom et. al

 

I've tried the old screen again just to verify that it does not work - Verified. Just for "grins" I've pulled the entire laptop apart (whew - 40 screw later) and do not see any specific "loose" connections on the main board. I can turn on the lapto (minus HD) but again no light on the old board - decided to try that first since its already defective and in case I do something funky.

 

If anyone has a schematic/diagram of this particular Sony MB or layout and can find the connection to the video (nVidia Geforce ? model), perhaps I can test the output to the screen, otherwise I think this is a lost cause.

 

Thanks for the effort/feedback, I hope someone has further thoughts.

 

Dave

Expert:  Dan replied 3 years ago.
One potential area to check would be whatever shuts the backlight off when the lid is closed. I'm not familiar with that particular model but some will use a proximity magnetic reed switch or a physical switch that opens/closes as the lid comes down or opens.


Dan
Customer: replied 3 years ago.

Hi Dan,

 

Thank you for that suggestion. I've checked the hinges - removed the screws, then replaced them w/o any luck. After removing, I tried to look behind to see if there was any kind of switch, but I've not been able to find anything that even remotely looks like a reed/button switch. If anyone knows if and more importantly where it might exist, that might actually be the problem since I can't see anything that has been disconnected, burned or otherwise shorted on the board or connector.

 

Thanks again for the idea.

 

Dave

Customer: replied 3 years ago.
Relist: Other.
Thank you everyone for trying to solve my problem, I'm still looking for someone who might have an answer to the "backlight" question. As reported, I've essentially taken the laptop completely apart w/o finding any other problem. I've also looked for a "reed switch" (thank you Dan) but have had no luck in ferreting out a location and/or switch.

It is certainly possible that the LED "backlight" has failed completely on the new LCD and simultaneously on the old LCD, but that seems an unlikely scenario. Further if anyone can check the numbers, the replacement LCD is a compatable replacement, not exact. I do not have a cross-referrence table/chart. (see previous post for #).

Thanks again for all the suggestions, it is a shame that a little computer that still operates has failed after only 14 months and Sony offers no help or even troubleshooting assistance.

Dave

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