How to test a LCD screen?

NessdufratNessdufrat
Posted:
in Genius Bar
hi there! Odd question coming... I found an iMac in the trash (yep). iMac late 2013. Screen was broken (the glass. The lcd seemed undamaged), there was a big problem with the power button, and hard drive had been removed by previous users. After trying a few things, I was able to revive it, I'm now waiting on a hard drive that a friend of mine is sending me (he put ssds in his Mac minis so he was willing to part from one of the hard drives), but I already tested it on an external screen and downloaded the OS on the ram and it seems to be in good working condition. Thing is, apart from the fact that the glass is broken in several places, the lcd seemed fine, and I feel very frustrated that after checking and double checking all connections, it still doesn't work and doesn't light up.
the led on the motherboard, 4th led, the one that tells if there is a problem with the screen or with communication between motherboard and screen (or graphic card and screen? Can't remember. Lvds connector is attached to the motherboard) doesn't light up, which, according to Apple, can mean the screen needs replacement or there's a problem on the motherboard. Great. Lucky day. 
I live in France, I checked all around for a broken compatible iMac to test the screen, no luck so far. I very much doubt I can barge in an Apple Store with my lcd in a big tote bag and ask them to test it for free, even though I know it will take them about four and a half minutes. I'd be willing to buy a screen if I can be sure that the problem is indeed with my screen and not somewhere on my motherboard, but if I have to pay $150 + shipping and taxes and then the brand new screen stays black, I'll be very very sad (and I'll eat pastas for a month).
is there something I could do on the screen itself, something more I could test? I checked the connections when I put the screen back, I also unscrewed the screen to check some connections there, everything seemed fine, the lvds connector(s) (I guess one is for the webcam) seem great too, but are they the kind of very fragile thing? Maybe I could start by ordering a new one?
thanks for all advice!
imac model is a1418, it's an iMac 21.5". I guess I could live with it not having a screen and using two external screens, but I'm unsure of how it will behave without its own screen (like maybe sometimes it will prompt me for some stuff on the broken screen and I won't be able to see it, and maybe it will be clever and since it knows that the connection is faulty, it will bypass it altogether to directly go to the external screen).

Comments

  • Reply 1 of 3
    1st1st Posts: 443member
    if you checked all connections, it still black.  it might be the back light gone... if it is the fault, you might have to get a new screen or use external (if you can test using external).  the back light is usually integrated in the screen with diffuser, reflector... you don't have good chance to just replace it alone.  imho.  best of luck.  glad you get so far as to revive the imac.  i am still using G4 version of mac (half ball type) with motorola processor.  you are way ahead of me.  
  • Reply 2 of 3
    FrogbaitFrogbait Posts: 6member
    Black shiny minature Monolithic iPhones may be in - but I would like to see the genuine Titanium iPhone - non-magnetic, shiny grey exterior and strong enough to be ran over by a bus and only get minor scratches on its case!Hugo Shepherd.
  • Reply 3 of 3
    NessdufratNessdufrat Posts: 2member
    I'm not so sure about the backlight. I did the lamp test (where you put a lamp right in front of the screen in a dark room and you try to see if something is on the screen), and I saw nothing at all.
    I'm still waiting on my hard drive (probably lost in the mail somewhere) and I'm becoming increasingly frustrated, and I can't test anything without it (especially the usability of the computer without the main screen and with the two external screens). I found a second hand screen, it would cost me about $100 total to get it, but I already ordered the lvds cable (will take forever to arrive too, with any luck it will be here before the hard drive) and I'd like to test this solution first. It would be stupid to waste $100 on a screen if the problem is with the cable. It could be the cable. It could also be the screen not getting any power from the motherboard because the connection is faulty, and getting a new screen wouldn't fix it. I don't really like gambling :/
    On the a1418 mac, the lcd is one piece. You can't replace one part. The glass, the backlight, the lcd are all together. 
    My glass is broken. If I manage to fix the screen and the cracks really bother me, I might try to gently remove the glass panel (but I'm not really sure it's doable) because I must say I'm not a big fan of the glossy screen. I have it on the thunderbolt and on the macbook pro too (I used to have the mate screen, but the mac was stolen, and then apple wasn't making it anymore (macbook pro 17) and the only one I could find second hand that was like mine (quad core 2.5ghz) was with the glossy screen, so I didn't have a choice. It's a huge difference. Glossy screen is horrible). Anyway, that would require fixing the screen first. And right now, I'm still far from a solution...
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