Question Intermittent Flickering External Display - Basic Electronics

danallenhtn

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Oct 8, 2016
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Looking for help understanding what hardware is the failing culprit.

U28D590 Display Samsung 4k 28"
Been running current configuration for years
Computer is 2012 MacPro (cheese grater)
AMD Radeon HD 7xxx 3 GB Graphics Card
HDMi out of computer to HDMI port (1.4) on monitor

Symptom: varies
.. Can be mild flicker of screen every several seconds
.. Can be mostly dark gray screen with horizonal lines flickering wildly showing narrow fragments of what should be on screen
.. While system is running normally, problem never pops up
.. Problem appears when the computer awakes from sleep or restart of computer

Switching to another monitor with its own internal power supply eliminates problem

I suspect the problem is in the power supply's capacitors, but I don't know if symptoms would be caused by that.

Things that have no effect:
Changing screen resolution
Changing refresh rate

Usually, the problem disappears by unplugging/wait_5_seconds/plug_back_in the power supply for the display unit from the AC source.

Problem has been becoming more frequent. Yesterday, I could not make problem disappear, had to switch to backup display (big downgrade)

Now it is working perfectly.

Power supply provides 14 volts DC to display.

Backup monitor has internal power supply, plugging directly into 120V AC
 

jay32267

Illustrious
You could always put a meter on the supply voltage.
That would tell you if you had a supply problem or a display problem.
I'd suspect the display over the supply....because in my experience I've had it be the display way more often.
 

danallenhtn

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Oct 8, 2016
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You could always put a meter on the supply voltage.
That would tell you if you had a supply problem or a display problem.
I'd suspect the display over the supply....because in my experience I've had it be the display way more often.
Thank you for responding to my question.

I don't know much about how flat panel displays work. The reason I was suspecting the power supply is I have the impression the problem most likely is caused by bad capacitor used for transforming 120 AC to 14 DC. Since the power cord has a transformer built into it, I thought that is where the problem would be.

Today, I have the display running normally. Yesterday it was unusable.

Naturally, I want to fix instead of replace the unit. I really don't know where to go from here.
 

danallenhtn

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Oct 8, 2016
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you probably need a DP 1.4 certified cable
Thank you for responding. I bet you are right. One thing I am curious about. I have been running an HDMI cable for years without problems of any kind. Any ideas why problem would appear after all this time running HDMI and why switching to DP would make a difference?
 

nneo

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Feb 25, 2011
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I'm really not sure about your problem, but it's worth a try with a better HDMI cable at least, just don't use the bundled cable.
 

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