Any ideas on an Apple Cinema 30 problem - Page 1
Forum section: electronics / projects

author: alanambrose
author_rank: Frequent Contributor
timestamp: February 13, 2014, 06:34:49 pm
content: I have an oldish Apple Cinema 30 screen. This has dual-link DVI. It's just recently started acting up and gets a green fuzzy random geometric pattern over the entire screen from time to time. Makes the screen unreadable. Usually, I just switch it on and off again and its immediately always fine - at least for a while. Yesterday, it started doing this bigtime (just as I was trying to finish a grant application, go figure). Today, playing around I see that if I switch it to 1280x800 instead of 2560x1600 it's solid again but I'm losing resolution like crazy. I have another identical screen which has always been solid - swapping the video board connection (it's Windows/NVIDIA) and/or power supply brick over makes no difference. Some kind of marginal sync problem in the screen maybe? Any ideas how would I go about debugging and fixing it?TIA, Alan

author: dr.diesel
author_rank: Super Contributor
timestamp: February 13, 2014, 08:17:43 pm
content: I don't' recall the symptoms, but Gerry Sweeney did a video on repairing an Apple display not too long ago. Look him up on Youtube, might help you out.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: February 13, 2014, 09:17:28 pm
content: Theres an old post on the apple forums that might help :https://discussions.apple.com/thread/221199?tstart=0

author: dfmischler
author_rank: Frequent Contributor
timestamp: February 13, 2014, 09:33:03 pm
content: Have you opened it up and looked inside for bulging or leaking capacitors? How about brands/series known to fail? This might not pan out but it is quite common in the industry.Of course, while you're in there check for excessive dust, fans that don't work, scorched components, etc.

author: alanambrose
author_rank: Frequent Contributor
timestamp: February 13, 2014, 10:11:43 pm
content: Thanks, interesting leads, I'll check them out, and I hadn't seen those particular conversations before. Seem to be a few different problems with Apple screens ...'scuse my ignorance of video - but what does reducing the res from 2560x1600 to 1280x800 do which apparently makes the screen move from unstable land to rock solid?Alan

author: dfmischler
author_rank: Frequent Contributor
timestamp: February 13, 2014, 10:14:50 pm
content: Quote from: alanambrose on February 13, 2014, 10:11:43 pmReduces the pixel rate by a factor of 4. And that considerably reduces the power used (i.e. heat generated).

author: wraper
author_rank: Unknown
timestamp: February 13, 2014, 10:49:42 pm
content: Reducing resolution forces to use only one DVI link of instead of two and 4x lower bandwidth in total (2x lower DVI frequency as bandwidth was already halved by disabling the second link). So very likely problem is related with that.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: February 13, 2014, 11:45:21 pm
content: Quote from: dr.diesel on February 13, 2014, 08:17:43 pmI thought of that when I saw the subject but his monitor had the backlight out in half of the display. He fixed it by soldering the wires into where the connector was fitted.

author: alanambrose
author_rank: Frequent Contributor
timestamp: February 15, 2014, 10:07:46 am
content: OK let me document where I am in case anyone else ever needs this info. Excuse me if I use the wrong terms because I know nothing about video ...There are a few well known problems with Apple screens / iMacs. At least these:+ the 'backlight connector problem' that Gary S described and fixed.+ a capacitive on-off switch problem that causes the display to switch itself on and off, particularly when coming out of sleep mode. Can be fixed apparently by obscuring some pins on the power connector.+ the kind of 'clocking or sync problem' like the one I've got.Regarding the latter, some people have reported success by reducing the vertical refresh rate from 60 (actually 59.804) down to about 58. This can be done apparently with a utility called PowerStrip ($30) on Windows and SwitchResX on Mac. There's a post here:https://discussions.apple.com/thread/221199?tstart=0There's a screenshot of PowerStrip attached that shows the kind of thing. As dfmischler said, you can see the pixel clock reduce by 4 from ~288 MHz to ~71 MHz when reducing the resolution from 2560x1600 to 1280x800. I will play with this a bit more but the PowerStrip adjustment doesn't seem to work in my case. I can reduce the vertical refresh rate bit by bit from ~60 to ~57 Hz at which point the screen goes black and it refuses to sync altogether.There's not much info on teardown but the best I found was this:http://jan-schulze.com/disassembling-an-apple-cinema-display.htmlThe thing I'm puzzling over at the moment is what kind of fault could cause this kind of failure, given that it seems to be relatively common but intermittent. For a long time the sync was temporarily fixed on my unit (and reported by a lot of other people) just by switching the thing on and off. Some days it would be bad, sometimes it would go for weeks without a problem.Alan