EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: rezise on August 14, 2017, 05:36:15 pm
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Hi!
I have three Vizio E241-A1 panels that I got refurbixhed for really cheap. But one of them intermittently powers itself off!
It happens seemingly randomly. The screen will just shut off. Once this happens, I have to unplug it and re-plug it in for it to turn on again. But after a while (sometimes a few weeks, sometimes days) it will do the same thing; then itll happen again after a few days/hours; the next time hours/minutes, until eventually it cant even power on. Very strange.
Now, that is a clear cycle I have noticed over the past 6 months. Once its powering itself off every hour or so, I just open the TV up, push all the wires down and make sure all connections are secure. Then the screen works again, and wont power itself down for at least a month or so.
Any ideas what I can do next to revive this thing?
(https://www.ocf.berkeley.edu/~sraman/pictures/20170814_091725.jpg)
Thanks!
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Electrolytic capacitors are one of the most common sources of failure. Based on what you've described, it'd be good to check for poor solder joints, cracks in the PCB, and broken traces. The behavior sounds very much like a solder joint (e.g., on the cable sockets) that, after a number of heat/cool cycles, loses its connection.
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Thermal cycling is the first thing that popped up in my mind as well.
Checking for brown can be helpful as well; brown spots would be hints for heat, and brown stains usually indicate electrolyte leaking from caps. Also look for bulging on your capacitors if you're unaware to do so.
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The boards get their ground through the board screws.
It could also be that the screws are loose. Try to tighten them down first. If you get more than a quarter turn out of any or some of them, that is all that the problem may be.
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All good tips. rezise, let us know what you find. And welcome to the forum!
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You mention in one section of your post that it just turns off, then in another you mention just the screen turning off, I'm not trying to be pedantic but does it completely turn off or does just the screen and you can still hear sounds ?
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Thanks for all the replies! Ill give them a go.
@jordanp123 it is the whole TV that powers down, no audio either. And once it auto-powers down, I have to unplug it for a few seconds before it will turn on again.
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I agree, with everyone to look at the solder joints. You can use a hair dryer or a hot air gun (at a safe temperature), with the TV on to try to mimimic the thermal effects, it can be useful to try to narrow down intermittent issues that are thermal related.
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So I took a look at the two boards' solder joints; particularly all the capacitors. I really coundn't spot anything ecan resembling a hairline crack in any of them. But I did notice something fishy.
Regarding what @JoeO said, it seems this board has a very convoluted way of getting grounded. Theres a screw on the board that connects a metal bracket to the board; and that metal bracket has thin fins that are supposed to touch the metal backplate. The metal is really thin and all bent out of shape, no doubt due to thermal cycling. What a terrible design!
I also found a lot of crud/oxide buildup between the screw and the bracket. I cleaned that off and bent the brackets in an exaggerated amount to force a good connection.
Now the screen powers up and switches channels much faster than before, and actually now just as fast as the other two! Ill see if the screen powers down in the next few weeks but now its performing better than the day I got it, so Im optimistic! Looks like fretting / oxide buildup was the likely cause, the screens weren't new so I suppose they could have been thermal cycled many times by the time I got them. Also, these screens seem to have verry underpowered PSU's and are susceptible to small ground fluctuations. When I power anything on thats on the same line as these screens, the screens all go dark for a second. So I suspect a poor contact could make them float intermittently. What a heap of junk but they were cheap!
Thanks for the help!
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If your fault occurs again after you have cleaned the grounds, check your standby voltage. Either 5V or 3.3V. If you don't have standby the fault is in the mainboard. If you do have standby, then the fault is in the power supply. Standby should be on the row of pins on the third connector from the left on the mainboard (green) at the bottom. You could also check for standby on the power supply, but just be careful. The audio is the last connector from the left.
Hopefully your problem is fix though.