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Problem with Vostro 3550 screen after repair

jimimak

FPCH New Member
Joined
Apr 8, 2015
PC Experience
Very Experienced
Hi all,

My first post to this forum so apologies if I'm not following the conventions...

Just a quick summary of myself as it may be of relevance - I'm no PC repair man, I am however, a fully qualified electronic engineer having done a 4 year apprenticeship with the MoD, although it was a few years ago. These days I'm a full time Java developer so dont tend to get too involved with hardware - I do however know my way around a soldering iron and a screwdriver and all manner of test equipment, anti-static protcols etc etc ...so feel pretty confident opening up a pc/laptop to make minor repairs.

Now that's out of the way - I inherrited an almost new Dell Vostro 3550 laptop with a damaged power socket - plan was to repair it for my son.

After a few googling/youtube sessions I throught it all looked fairly straightforward and set about opening up the laptop and replaced the small circuit board with the jack. Put it all back together again and powered it up. The laptop seems to start up fine getting through to the windows "chimes" suggesting it had started up fine - however the screen was blank. What was strange though the backlight on the LCD seemed to be on.

My first though was the flat cable on the back where the screen attaches to the mainboard - however that looked fine after opening it up again. I did try disconnecting it again and re-seating and after putting it all back together again tried again, - same result - laptop boots up, backlights on, nothing on the screen.

I then tried again, reverting to the original DC jack board - powering off the battery but the same - machine boots up, backlight seems to be on, but nothing on the screen.

I switched back to the new DC jack board having ruled that out as the old broken board yielded the same result - nothing on the screen.

I then tried connecting to a TV via the HDMI port, and that works fine - I see the login prompt and the LCD screen flickers briefly - or at least the backlight does as it switches to the TV via the HDMI port - so Im guessing this probably isnt a videocard problem

Ive checked and checked again the connectors and cable from the LCD look fine, and I was extremely careful each time when I disconnected and re-connected it.

I know the LCD on the laptop was working fine before I replaced the DC jack board so it definitely something Ive done.

....so what would you suggest I try next ? ....not sure its worth going to the expense of buying a new LCD unless I can be certain thats broken. Can I get just the cable in case a wire inside has come adrift ?

....or is there anything else you can think of that would stop the LCD from displaying anything, yet the machine still boots up and works via HDMI - just seems strange the backlight on the LCD (or at least I think its the backlight) is coming on and flickering when I switch the video out to the HDMI port

...is there some other thing I need to do to get the mainboard to see the LCD screen after disconnecting it ?

Starting to loose count of the times Ive had this laptop open now so any suggestions would be most welcome.
 

Plastic Nev

Deceased - sadly missed
Joined
Oct 19, 2008
Location
Lancashire
Hi and welcome to Free PC Help Jimimac.
Considering that there is at least digital output via the HDMI port suggests that part of the graphics system is working OK, I would have been a little happier if the laptop has a VGA port and an ordinary monitor tried, as that would be full proof that both the digital and analogue of the graphics was OK.

However as you yourself suggest there is a possibility you disturbed something while replacing the DC input jack, so I can only suggest a good examination of the cable from the motherboard to the laptops screen.
If the backlight is definitely seen, it can only be the video signal not getting there. Check connections of that cable by fully removing each end and replacing if they are on plugs and sockets.
If you have a meter, check conductivity of the cable while it is off and bend the cable back and for, those cables are prone to breaking a conductor especially where it goes round or past the hinge.

Nev.
 

jimimak

FPCH New Member
Joined
Apr 8, 2015
PC Experience
Very Experienced
Thanks Nev - I'll give it a go a post back as soon as I get a chance.
 
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