Second Display Flashing To Black

Question

Level 1

1 points

Second Display Flashing To Black

I am trying to get a 22" Samsung display working with an iMac 8,1 (mid-2008). Connected via DVI-D cable and Apple DVI to mini-DVI adapter.

The Problem

External display flashes to black intermittently when operating the iMac. When it is idle the monitor is stable. Sometimes the display will operate normally for a period of time and start flashing again, seemingly at random. This machine previously ran dual displays with no problems. OS is Yosemite 10.10.2

Have reset SMC and NVRAM maultiple times, repaired permissions, shutdown, unplug, replug, etc...everything except reinstalling the OS.

I booted into a 10.9.5 (Mavericks) partition and get the same flashing problem. Booted in old OS 10.5.8 (Leopard) partition and the display works as it should.

This machine ran dual displays under both Yosemite and Mavericks without any issues until recently. The LG 23" monitor that had been hooked up since 10.5.8 went black a few weeks ago, likely a blown capacitor since it didn't work with any computer or OS. The Samsung is the replacement for the dead LG and the flashing to black was never an issue before the LG.

Frankly, I'm stumped and open to suggestions, advice, hunches..anything that can get this setup working as it was before.

Thanks in advance!

Posted on Mar 25, 2015 2:41 PM

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Answer 1

den.thed

Level 9

77,044 points

Mar 25, 2015 5:26 PM in response to jeanjeudi

You know, that sounds more like a failing DVI adapter or loose mini-DVI port on the back of the iMac, than the external monitors.

1. I would try a new Mini-DVI to DVI adapter and a different DVI cable.

2. I would also make sure that the weight of the DVI cable is supported and not pulling on the iMac's Mini-DVI port.

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Answer 2

jeanjeudi Author

Level 1

1 points

Mar 26, 2015 2:56 PM in response to den.thed

Thanks for replying.

The LG is toast...it doesn't work with any machine or OS. I suspected the cable or adapter too but what I don't get is why the monitor works perfectly when the machine is booted into Leopard 10.5.8 but does the funky flash dance when Mavericks or Yosemite is running.

If the adapter or the port is the culprit can it be that Mavericks and Yosemite process DVI signals differently than the older Leopard OS and are more sensitive to a loose connection in the mini-DVI port or adapter?

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Answer 3

den.thed

Level 9

77,044 points

Mar 26, 2015 4:27 PM in response to jeanjeudi

Could be your GPU is over-heating in the later OSXs and/or is already damaged from age and over-heating.

(not sure it you have the HD 2400 XT or HD 2600 Pro...?)

When was the last time you cleaned out the air intakes or had it cleaned and serviced to make sure it is cooling properly....?

Edited to add > https://support.apple.com/en-us/HT201177

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Answer 4

jeanjeudi Author

Level 1

1 points

Mar 26, 2015 8:41 PM in response to den.thed

It's not my machine, I'm just the repair man tasked with getting the monitor functioning properly. But knowing the owner I'm certain it is very dusty inside and has not been cleaned in a while, if ever.

The GPU is an HD 2600 Pro. The computer does run quite hot and the fans have to be software boosted to 3500-5000 RPM to keep the computer from overheating. Sometimes an external fan blowing air into the bottom air intake is necessary. I had a similar model iMac (7,1) exactly the same specs except a year older, and it ran much cooler than this one and I never changed the default fan speeds. I currently have an iMac 13,2 (mid-2012) and the air intakes are bigger and more efficient than the 2007/2008 models and the aluminum back panel helps keep it cooler than the black plastic on this model. Still, it gets hot and apparently if you're using to power a TV or play games it can cause problems.

As far as hardware quality my old G5 tower (sadly I sold it...that was one for the museum) beats any iMac or the new MacPro. Some upgrade options would be nice on these machines...I'd rather have that than a slimmer, lighter computer every few years. What keeps me buying Apple is OS X...and the smooth almost seamless integration between iOS and OS X. iOS is best jailbroken..stock is a little bit too locked down for my liking. I'd consider building a Hackintosh if I had the time, know-how and a high tolerance for constant troubleshooting, but I don't, and for my needs the iMac line is still good. Not perfect, but I haven't any major problems yet. /Off-topic interlude

Strangely enough today, or at least for the last few hours, the display is working as it should. I have gone through all the steps in the link, except Safe Mode. Maybe I will try that.

My advice to the owner is plan to get a new iMac soon, or at least a newer one, rather than sinking more than just spare change into repairing this one. In the meantime cleaning the inside and replacing the DVI adapter (thanks for those suggestions) and I suppose re-installing Yosemite is an option. The fact that the display works perfectly with Leopard even when the machine is hot is still a mystery. And the other monitor was working fine with Yosemite before it died. Could a power surge have done something? I will bring a newer monitor with me tomorrow and test it against this one.

Thank you again for the extra suggestions!

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Answer 5

jeanjeudi Author

Level 1

1 points

Mar 27, 2015 1:27 PM in response to jeanjeudi

Hooked up a 23" LG monitor and it also flashed to black, albeit not as frequently as the Samsung.

Rebooted into Safe Mode and the display works perfectly. Deleted the com.apple.windowserver.plist as recommended, booted back into 10.10.2 and it's back to square one. Looks like an OS re-install might be in order.

Just to clarify, does the display working in Safe Mode rule out a GPU or display port/adapter problem and point towards an OS issue being the cause?

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Answer 6

den.thed

Level 9

77,044 points

Mar 27, 2015 4:36 PM in response to jeanjeudi

Along with other functions, Safe Mode disables Accelerated Graphics and Yosemite's Translucency feature.

see > https://support.apple.com/en-us/HT201262

I would try reducing the transparence in System Preferences > Accessiblity > Display while booted normally to see if that helps....?

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Answer 7

May 27, 2015 3:30 PM in response to den.thed

I just installed an SSD in my mid-2007 iMac. As I've been running under Mountain Lion, I thought I'd take this opportunity to upgrade to Yosemite. Upon completing the install, I encountered this 'flashing to black' issue on my external monitor. But when I reboot using the original drive, now mounted externally, and still running Mountain Lion, the display works as it always has. This tells me the hardware is fine - the variable is Yosemite. Therefore, I submit this is a Yosemite/software issue, and has nothing to do with how clean the insides of the computer is, or any other sort of hardware failure.

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