EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: stan001 on June 13, 2021, 05:40:58 am
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Dear all,
I have this strange behaviors of an old Dell monitor ( Dell U2312HM ) that died ( totally no power ) after a sudden power trip ... and comes back alive a few weeks later...
The 1st time this happens, I ordered replacement parts for the display board ( the board have 2 boards - a power supply board and display board taking in various voltages from the power supply board )
I can confirm it was NOT the power supply board that died.
Anyone knows why this happens ?
Are there some type of "special fuse" that prevent it from powering up like PTC ??? And after a few weeks of discharged ... comes back alive again ???
How do I speed up the "discharged" to bring back the monitor alive again ?
Image of the display driver board..
(https://live.staticflickr.com/65535/51244185644_96b45ab0a5_w.jpg) (https://flic.kr/p/2m5gR59)Dell U2312hm (https://flic.kr/p/2m5gR59) (https://www.flickr.com/photos/stanleyseow/)
Thanks
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Are you SURE about the power supply? I have fixed a lot of dell monitors and it's pretty much ALWAYS capacitors. I'd suspect the kick start capacitor on the power supply. It's usually a small value one.
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Uh, how exactly can you "confirm" it's not the power board? Correct me if I'm wrong, but it is my understanding from your post that you've only replaced the display board (and not the power one too!) and it's very likely that the issue is on the power board. And FYI, this particular model has a common fault with the 3.3V voltage regulator (G1084-33) so that's prob the first thing you'd wanna check.
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Dear all,
I have this strange behaviors of an old Dell monitor ( Dell U2312HM ) that died ( totally no power ) after a sudden power trip ... and comes back alive a few weeks later...
The 1st time this happens, I ordered replacement parts for the display board ( the board have 2 boards - a power supply board and display board taking in various voltages from the power supply board )
I can confirm it was NOT the power supply board that died.
Anyone knows why this happens ?
Are there some type of "special fuse" that prevent it from powering up like PTC ??? And after a few weeks of discharged ... comes back alive again ???
How do I speed up the "discharged" to bring back the monitor alive again ?
Image of the display driver board..
(https://live.staticflickr.com/65535/51244185644_96b45ab0a5_w.jpg) (https://flic.kr/p/2m5gR59)Dell U2312hm (https://flic.kr/p/2m5gR59) (https://www.flickr.com/photos/stanleyseow/)
Thanks
no you can't unless you scoped your voltage rails
like others, my bet is on caps or some cold junction
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Uh, how exactly can you "confirm" it's not the power board? Correct me if I'm wrong, but it is my understanding from your post that you've only replaced the display board (and not the power one too!) and it's very likely that the issue is on the power board. And FYI, this particular model has a common fault with the 3.3V voltage regulator (G1084-33) so that's prob the first thing you'd wanna check.
Previously I ordered both the power board and the display board, the power board was fine, I replaced both the display board.
Yes, I will order and swap out both the vreg ( G1084-33 ) first...
Thanks
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Previously I ordered both the power board and the display board, the power board was fine, I replaced both the display board.
Yes, I will order and swap out both the vreg ( G1084-33 ) first...
Thanks
So you're saying you ordered the power board and display board and when you replaced both of them did did the exact same thing??
How did you confirm the old power board is fine? If you say it is fine then why are you about to swap out the voltage regulator? If that component needs replaced then the board is clearly not fine.
Not making much sense here. :palm:
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Yes, I will order and swap out both the vreg ( G1084-33 ) first...
Hold your horses. How bout measuring the voltages of the existing first? See the attached image.
Also, just so you know, G1084-33 is only available in China (means you could only get it from places like Aliexpress/Ebay, and that the shipping may take a while) From the other hand, AZ1084CD-3.3TRG1 is also compatible and has better availability.
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Lots of Dell equipment has a surge protect circuit in the power supply. This will lock the power supply and prevent it from starting. The way you reset it is unplug the power supply and let it sit. All capacitors need to discharge to get the supply to reset. After that it will work just fine till it sees another surge again and trips the lock out circuit. I do agree with everyone as well caps are usually and issue in these but it this case I am betting lock out circuit. I have "fixed" hundreds of dell computers by resetting the power supply.
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Lots of Dell equipment has a surge protect circuit in the power supply. This will lock the power supply and prevent it from starting. The way you reset it is unplug the power supply and let it sit. All capacitors need to discharge to get the supply to reset. After that it will work just fine till it sees another surge again and trips the lock out circuit. I do agree with everyone as well caps are usually and issue in these but it this case I am betting lock out circuit. I have "fixed" hundreds of dell computers by resetting the power supply.
https://www.youtube.com/watch?v=nn2FB1P_Mn8 (https://www.youtube.com/watch?v=nn2FB1P_Mn8)
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Not coming back on after a power failure, especially if it's normally left on all the time or for extended periods is almost always the cap in teh startup supply - look for a low-voltage electrolytic cap on the mains side of the PSU & replace it.
Very common in things like VCRs/Set-top boxes etc.
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Lots of Dell equipment has a surge protect circuit in the power supply. This will lock the power supply and prevent it from starting. The way you reset it is unplug the power supply and let it sit. All capacitors need to discharge to get the supply to reset. After that it will work just fine till it sees another surge again and trips the lock out circuit. I do agree with everyone as well caps are usually and issue in these but it this case I am betting lock out circuit. I have "fixed" hundreds of dell computers by resetting the power supply.
https://www.youtube.com/watch?v=nn2FB1P_Mn8 (https://www.youtube.com/watch?v=nn2FB1P_Mn8)
Interesting video however. I work on Dell equipment professionally all day long I have run in to this issue in servers, optiplex, Insperon, Latatude, laptops, printers, and monitors on SFF, USFF, and micro resetting power supplies is normal operation after storms. The issue is so prevent we don't even go on site any more until a reset is tried. I have run it to is so much now that I have to think it is intentional rather then a bug. In the 240 Watt SFF power supplys why is there so much circuitry in there when all I get is 240 Watts of ATX power.
Also if you open up some of the SFF or USFF power supplies. They are FAR more complex then they need to be especially for the wattage's that they run in In the server world I have even run in to power supplies that hand shake to the mother board and I have had a main board refuse to start with out a DELL power supply installed in the server. I have had a T330 Server not boot with a brand new Corsair 850 Watt ATX PSU. Tried it cause the server went down over the weekend and could not get parts till Tuesday. Plugged the Dell Supply in to the server and off it goes. I have to imagine that I2C is coming out the of supply to the board some where
By the way the reset interval is not weeks it is however over 30 Seconds to a minute. You can some times speed up the process hitting the power button a few times to get the supply to try and start it pulls the charge out of the caps faster. If you unplug and re-plug to fast supply does not discharge and the reset does not happen.
Which is also why I used FIXED in "quotes" because you are not really fixing anything but it does bring the unit back in to service and the user is happy again so as the tech you did "FIX" it in the users eyes.
Just some interesting observation from a Tech that works on this stuff all day long.
Zen