G5 imac intermittent yellow screen

Hey guys, I did some searching and didn't come up with anything, so I figure I'd see if anyone has any ideas on diagnosing this. The machine is my wife's old desktop, a very lightly used '05 G5 imac 1.8 and basically it started this issue a little over a year ago. It was originally just an occasional thing, but now it's like this probably half the time.

First of all, it wasn't one of the serials on warranty extension for video/power issues and it's never had the lines or distortion on the display that those units did. And yes, the capacitors are fine. Really, it's in perfect operating condition outside of a strong yellow 'tint' that comes and goes with no rhyme or reason. Sometimes it lasts a few minutes....sometimes a few hours. Booting is a coin toss, and you can shake, smack, or probe it with no affect.

We did have it at an apple store once around the time when it started, but they pretty much had no clue since it wasn't yellow at the time and the hardware test is fine. They just listed a bunch of expensive stuff that 'might cause' such a problem, said it was likely the logic board's integrated video component and were all too quick to point out that it would be a better investment to buy a new machine instead. We ultimately did just that, but mainly because my wife really wanted a notebook and the release of the unibody 13" was perfect timing for last xmas, lol.

But this thing just still bugs me and it would be a nice unit for the garage or something, so last week I dug it out of the closet and picked up a mini-dvi video adaptor to attach an old external vga display I had. Interestingly enough, the video out signal is clean, so now I wonder if the worse case scenario (logic board) is even capable of being the cause. Could it be the LCD itself? I have no problem with replacing whatever it needs myself; I just don't want to dump a pile of money into what is essentially now a $500 machine by blindly replacing parts. Here are some pics that show the difference......I'd really appreciate any ideas or opinions. Thanks.




Funny seeing the horrible resolution that the external forces when you enable video out, haha.

Have you checked the connection where the LCD display plugs into the Mainboard? I have a newer iMac G5 20" iSight and mine has a small plug that plugs into the Mainboard and is held with 2 small screws. If yours is similar, loosen it up and jiggle it and see it if goes yellow. One color is going away leaving what looks like Green and maybe Red so maybe Blue. Try cleaning the plug also. Check the cables on the back of the LCD also. I have never worked on the older iMac G5 like yours but the basics should be like mine.

Good call.

Sure enough, even though all the various shaking and poking around I've tried wouldn't make a noticeable change, a bit of wiggling on that connector retuned immediate results, ranging between blue lines to the yellow cast. Interestingly enough, after messing with it for a while trying to determine if it was the cable or the board outlet, it rapidly got worse, starting with all kinds of colored lines that required more and more pressure on the rear of the plug to 'clear up' and ending with a total loss of video to the lcd. Nice. Oh well, the external still works.

I pulled it apart further to day to get a good look at everything and both sides of the logic board appear fine, at least to the naked eye. I unwrapped the plug end of the cable a bit and unsoldered the grounding cover to try and get a look at the terminations, but it's comprised of microscopic coax who's connections are sealed over with some type of clear resin and way too small for my eyes to properly analyze anyway, haha.

The cable for that particular generation are unavailable separately (of course), and evidently the later isight versions won't work, but I managed to find a used one on evilbay for twenty bucks, so we'll see what happens.....I'll update with the results when it comes in.

If worse comes to worse, I suppose I can just pick up a decent size VGA screen and park it in front of the imac, lol. Thanks for the help and the lead, I really appreciate it.

I will almost bet it's that cable and plug. I hope the used one from Ebay is in good shape and solves it for you. Be careful when installing it as it seems very delicate.

Just wanted to make a quick update to provide info for future searches. Cable arrived today and it works perfectly. Thanks again for the great info. Saved me a big headache and now what was basically a useless machine once again has value and/or purpose.....for twenty bucks, lol.

Good going! Great to hear it works and that iMac still has some life left!

Yellow Screen

I have an imac G5 isight. About 1 month ago (after 3+ years) our screen decided to flicker to yellow. It goes back to normal only when we shut it down or wake it up from sleep mode. However, after about 5 minutes, it goes back to yellow.http://www.mac-forums.com/forums/mac_images/images/smilies/Frown.png

It seems you have found a cure. Could you tell me what the name of the cord is that you bought on Ebay and whether or not it was difficult to replace?

Thanks dtravis and ronlp for help in directing me on how to repair my
iMac G5 (yellowing screen as well) with ambient light sensor (which is now up and running fine after locating and replacing the LCD cable).
yay!

jcollins, to proceed in more detail to fix your iSight computer the following steps
might be helpful:

1)
(Getting familiar with the location of the LCD cable and how to
remove it without damaging other components in your iMac)
Before disassembling my computer I went to:

ifixit.com

to have a clear visual of my computers' internal construction and
location of the LCD (LVDS) (display data) cable connected with
two screws to the motherbooard on one end and to the LCD with a
flat metal plugin type on the other end (most likely) under a
black piece of plastic film with moderate adhesive to keep the
LCD end of the cable immobile. I peeled one end of the plastic
ever so gently and used a plastic giftcard to remove it by sliding
it under the black plastic and then side to side so that no direct
vertical pressure is exerted on the LCD panel below:

For iMac G5 17" with iSight go to:
iFixit: Do-it-yourself Mac & iPod Repair
Model-A1144-Display/942/1
(Go Step 11, cable is referred to as display data cable)

For iMac G5 20" with iSight go to:
iFixit: Do-it-yourself Mac & iPod Repair
Model-A1145-Display/1143/1
(Go Step 13, cable is referred to as display data cable)

You can go back to the specific device (iMac model you own, another
iSight 20" is on the website as well)

2)
Once I was comfortable with my computers construction I proceeded:

i) Unpluged all cables to my computer.
ii) I connected a bare wire around my wrist on one end to a grounded
metal object on the other end before proceeding to open my computer.
Any wire you can find will be adequate. Grounding yourself prevents
electrostatic discharge (static electricity from walking on carpets
or petting your cat or dog) into the sensitive electrical components
(microchips, capacitors, resistors) within the iMacs plastic housing.
iii) Used ifixit as a guide to opening my iMac (or user manual)
iv) Plugged in my computer (yes, while it is open) being careful not to touch any metal
objects on the motherboard, inverter that also connects to the
display or power supply
v) Located the LCD cable near the mother board
vi) Turned on my computer by using a set of tweesers to connect the
two contact pins (loacted in the same spot where the plastic white
housing has an ON button) and pressed down (lifted it in my case to
see the display)
vii) While keeping an eye on the LCD display output (lit, blue,
yellow ?) I wiggled the LCD cable (black color cable in my case) leading
up to the two screw attachment to the motherboard (big blue board
with many microchips, resistors, capacitors and other pertinent
circuitry) and saw if I could reproduce my display abberation
(yellowing, even other color changes).
viii) Shut off power as in vi) and disconnected the power cord.


3)
(Searching for the cable online)
I have an iMac G5 17" 1.8 GHz with ambient light sensor without
iSight

i)
The cable search on ebay (used for $20.00) I queried used the
following search terms:

--iMac G5 LCD cable
--iMac G5 LVDS cable

The options on ebay for an LCD (LVDS) cable for iMac G5 are
differentiated by screen size, frequency (example: 1.8 GHz vs 1.9 GHz)
and the option of iSight. I am not sure if one model cable can be
interchanged for another (i.e. an iMac G5 17" with or without iSight).
To be safe I just found the cable fitting the identical spec of my iMac
which happened to be: iMac G5 17" 1.8 GHz with ambient light sensor
and without iSight.

ii)
Another option is to go online to:
Apple iPod Accessory iPod Accessories Mac Software Mac Memory Apple Repair Store
Toll Free : 800.588.5290


The cable tends to cost between $50 and $70 depending on whether the
cable is used or new.