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Old 12-16-2016, 05:23 PM   #66
cmg
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Join Date: Dec 2016
City & State: London
My Country: United Kingdom
I'm a: Knowledge Seeker
Posts: 31
Default Re: A guide on how to troubleshoot 2 seconds to black

I have two identical 27 LED monitors to fix. Both of these seem have this 2s to black type problem where they seem to power up, an image flashes briefly then they go back to standby.

I have a lot of experience in fault finding circuits but not with LED Monitors/TVs. Before I get going Id like to ask some general advice.

Specifically Id like to get some advice on how to test the PSU isolated from the logic boards. I can see that there are various fault conditions where the power is shutdown deliberately by protection circuitry for instance going into standby when there is no signal, shutting down then the backlights are faulty etc. Id like to know how to test the PSUs in LED monitors/TVs with the logic circuity and screen unplugged so that I can check the PSU itself first. As far as I can tell, if the PSU is simply unplugged from the logic circuits, it would remain shutdown like a PCs ATX PSU does, so couldn't be tested without some test circuitry.

There are two reasons I want to approach it this way:
1) I want to isolate the problem. For this type of issue where the appliance seems dead it is logical to test the power supply first, and
2) These devices are clearly very dangerous to run live. I do have experience working with high voltage circuits (upto 1kV). The best advice for these is to avoid live diagnosis of the HT areas as much as possible. These circuits could be deadly. Having a methodical way of testing these would make the process safer.

I guess the advice to do this would apply to many monitors. The monitors I have are HP ZR2740W. I can't find the circuit diagrams for these so I cant work out the answer to this easily myself. Ill start a new thread for these monitors but if there is general advice perhaps it is best for people to find here.

Thanks in advance!
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