HP G7 1070us laptop w backlight issues

[brandonkick]

I've been working on this G7 1070us laptop for a friends sister. She claims
the screen was bad, because they couldn't see anything on it.

I did the "flashlight" test and the first time I worked on this (almost a year ago)
it didn't look like anything was on the screen at all. So for kicks I was taking apart
the laptop to gather information on what screen I needed to search for online
to replace this one. In doing so, I unplugged the connector on the back of the screen
and plugged it back in. After gathering all my information and putting the screen
back on the laptop, I fired it up and the screen is now working just fine.... I power cycled
it ten times and the screen continued to run. I ran the machine a day or two and that was
that.

Well it wound up sitting at my place for 8+ months as his sister never had the money to
pay me. So my friend (her brother) actually wound up borrowing the laptop from me
to use for some school work he had to do. It worked fine for him. He then gave it back to
me. Eventually she did pick the laptop up, and well now not even three or four months
later she tells her brother it's doing it again. So I get the machine back, tell her I'll look at
it because she paid me to fix it and it looks like it isn't fixed.

I fire up the machine yesterday and sure enough, dark seemingly dead screen.

I perform the flashlight test and after looking VERY hard (it's hard to see the black
win7 loading screen... only can see the little icon in the center) I do actually notice
the screen isn't dead it's just the backlight isn't working.

At this point, I figure bad inverter or a bad backlight bulb. So I get the numbers and
start doing some research. It turns out this is an LED backlight screen with an inverter
built into the screen.

After all that, my questions are:

What are the chances the inverter inside is bad?

Am I better off replacing the entire screen?

Any chance a faulty cable could be causing this, faulty connectors either on the screen side or motherboard side?

Why would the backlight start working after I reseat the cable on the back of the LCD?


How would you guys continue on with this?

I can buy a new screen and a new cable... I guess if I do that, and it still doesn't work then we know we have either A) something wrong with the motherboard or B) a second bad screen / cable? I did put some tape to secure the connector on the back of the LCD slot. I though maybe it's coming ever so slightly loose?


Would be easier if I had spares / stock lying around to trouble shoot.

 

[NYJimbo]

There is no inverter on an LED lcd screen. It's either the LCD logic board, the cable or the motherboard. It wouldn't hurt to clear the CMOS as some HP and Dell's have settings where you can lower the backlight to off and it will look dead.

Next time you get a laptop in for a cracked, but working screen, keep the screen for tests like this. That way you don't have to stock new screens if you cannot afford to.

 

[Larry Sabo]

So my friend (her brother) actually wound up borrowing the laptop from me
to use for some school work he had to do.

Really? So much for client data confidentiality, not to mention the impropriety of loaning their equipment without their permission. Who knows what goodies have been installed or data added or copied while it was on loan.

 

[brandonkick]

There is no inverter on an LED lcd screen. It's either the LCD logic board, the cable or the motherboard. It wouldn't hurt to clear the CMOS as some HP and Dell's have settings where you can lower the backlight to off and it will look dead.

Next time you get a laptop in for a cracked, but working screen, keep the screen for tests like this. That way you don't have to stock new screens if you cannot afford to.

Hmmm yeah. I'll try clearing the CMOS especially if I can get it to show up dead again. Do you mean doing a factory defaults in the BIOS or actually clearing it on the motherboard?

The problem with having a test screen is that for some reason, reseating the cable seems to fix it. If I disconnect the screen that is in there, to connect the test screen, and it works.... I really didn't learn anything since doing that made the other screen work as well.

This is a tough one.

I think I may just get a replacement screen and cable if it happens again (after trying to clear the CMOS) and swap them out. At that point, if it still happens, the laptop is junk as far as I am concerned. I doubt she will want to put a motherboard in it.

Thanks Jimbo.

@Larry Sabo

His sister knew and was fine with me loaning it to her brother. I just wasn't going to give it back without her paying for the cleanup / repair. I did ask first.


Thanks,

Brandon Kick

 

[Larry Sabo]

His sister knew and was fine with me loaning it to her brother. I just wasn't going to give it back without her paying for the cleanup / repair. I did ask first.

Ah, okay. Sorry, I got confused about which friend's brother you loaned it to. I thought it was an unrelated friend's brother. My bad.

 

[gadgetfixup]

You checked it on an external screen this last time right? It probably has good video?

There are only 3 pieces to the puzzle if you have good video on the external port. The jack on the mainboard, the lcd cable and the lcd jack (lcd) itself. Getting signal from point A to point B seems to be the issue. You need to check just 3 components to determine the problem.

I've seen those cables on the LCD get pulled sideways because someone put something heavy on the lid while it was closed. Not heavy enough to break the screen but enough to flex it and stress the cable. Of course you can check the lcd cable with an ohm meter if you have patience. I'd look closely at that connecter on the mainboard as well.

 

[Larry Sabo]

There are only 3 pieces to the puzzle if you have good video on the external port. The jack on the mainboard, the lcd cable and the lcd jack (lcd) itself.

Not always true, if I'm not mistaken. Some MBs supply VGA from the NB while others get it from GPU (which drives the LVDS, of course). So there are cases where you can have VGA video but no LCD video because of a bad GPU. VGA video doesn't guarantee a good GPU.

 

[brandonkick]

It appears that the video signal itself has never been an issue.... the screen always had output.

The backlight just isn't always working. I removed and re seated the cable at the LCD connector
again and the backlight started working again so I just put some packing tape over the connector
to keep the cable secure.

If it fails again we will start at replacing the cable, and then if it still does it we will look into a replacement
LCD.

I can probably resell both on eBay if it wind up not needing them, and I feel the customer probably wouldn't
take too big of a hit. Losing $25 on the cost of reselling the parts is well worth the gamble of solving the issue
I think...

The whole thing that bothers me though is that reseating that cable gets the backlight working again for a
period of time. Very strange. I could almost understand it if I got NOTHING to the screen and then reseating
the cable fixed it... but to only get video and no backlight..... then to remove and reconnect the cable to
have the backlight work again is just weird.