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Camelot One
Premium,MVM
join:2001-11-21
Greenwood, IN
kudos:2

Odd Toshiba laptop display problem

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It has been awhile since a repair has me this stumped. Its an AMD based Toshiba L675D. Hard to get a good picture of it, but the original screen shows this scrolling red background on dark screens, and a red ghosting on letters on dos screens. It occurs even in post/bios screens, with no hard drive, so it isn't a windows driver problem.

I've seen this before with a bad video cable, so I replaced it. Same result. The VGA output is perfectly normal, so it doesn't seem to be a video chip problem. Fan is working and temps look normal.

Next I ordered a used replacement screen off ebay. The ad listed it as compatible with this model, though the screen itself was from a different manufacturer. (stock screen is an AUO) With the replacement connected, as soon as the screen would normally light on power up, it just went to a bright white background with pulsing lines. I repeated the connection several times, both with the old and new video cables, always with the same result. Hooking up the old screen brought me back to the original red ghosting. Thinking I had just received a bad screen, I ordered a "new" screen off amazon, which was advertised under the exact part number of the original screen. Unfortunately they shipped a "compatible" Samsung model instead. This replacement wouldn't strike at all, unless I first power up with the old screen, then hot swap the cable to the Samsung. I would then get an image, without ghosting, but with a solid color background. (which varied from green to yellow each time I tried) I assume the background color is just a result of the hot swap, but I can't figure out why it won't strike on its own.

Aside from trying a 3rd new screen, does anyone have ideas? It sure seems like a video output problem, but I have never seen one go bad without also showing problems on the VGA output.


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23
Isn't the VGA output connector on laptops physically wired differently to the GPU? More specifically: isn't the D-sub connector wired to completely different pins/etc. on the GPU compared to the native LCD screen? You can use the D-sub connector to hook up a monitor and use it as a 2nd/additional display. At least on the laptops I've used from HP and Lenovo I did exactly this.

What I'm trying to say: the VGA connector working/showing things just fine in no way shape or form means the GPU itself is in working condition. There are shared, and separate, transistors for each display.

The problem is either one of the following, given the tests you've done:

1. Something amiss with the GPU on the motherboard or the related circuitry (between the GPU and the LCD itself -- yes there is some other circuitry involved, albeit minor).

2. Something amiss with the actual LCD display itself -- still cannot rule this out because the replacement LCD you got did not work. Unless you can get an exact replica laptop (same exact model, all the way down to revision), I dunno how you'd troubleshoot this.

{ranting}
FYI, I have yet to see any LCD screen bought off eBay advertised as "replacement for {model of laptop}" actually work -- I've tried replacing two of them in my time on Dell laptops, and both had different sets of problems (while the original/stock continued to behave an erroneous way, at least it got a picture to some degree -- much like yours), and also came with their own power inverters and so on. Maybe I just got unlucky both times, but whatever -- the moral I've learned is that vendors don't give a crap about laptops. They consider them expendable within 1 year, thus if something starts acting wonky on them, their response is "for a nominal fee we'll replace your laptop with a new/better model". It's virtually impossible, from what I've found, to get proper replacement parts for laptops which are over a year old.

As a result of my experience, I've adapted the following attitude: laptops suck universally, trying to repair them is a waste of time. The only parts that tend to work when swapped/replaced are the "user-serviceable" parts with bays, such as the hard disk, RAM, or (only sometimes) mini-PCI cards (wifi, etc.). Everything else acts like black magic, especially the GPU bits. I therefore just recycle those which go bad and invest in new ones. Laptops = industry cash cow. Another reason I hate the things...

If the laptop is under a year old, call Toshiba and make it their problem. In fact, you could even tell their support folks "look I'm a technician, just send me the exact LCD panel I need, P/N xxx-yyy, thanks".
{/ranting}

--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


captokita
Premium
join:2005-02-22
Calabash, NC
reply to Camelot One
I'm guessing this is an LED? (don't see an inverter on the 2nd pic)

The odds of getting 2 bad screens is unlikely, but it CAN happen. I had an issue with a Dell laptop that would only work right with a specific screen, any other screen would cause odd problems, being very dark, to artifacts, to just not working. So it's POSSIBLE, just not likely.

I would suspect a bad video chip. There's also a chance you have a bad cable - even the new one. Check for any pinches on the cable.


Camelot One
Premium,MVM
join:2001-11-21
Greenwood, IN
kudos:2
The 3rd display yielded the same results, so I just convinced my client it was time for a new laptop. He is now happy with a new Asus, and this Toshiba has been sold to a craigslist buyer who only cared that the VGA output worked normally.