Dell U2311H, display turns off after some time, requires unplugging to reset

[Phinnegan]

I've got a Dell U2311H, which will operate for some amount of time, and then turns off and becomes completely unresponsive (no LED, no voltage on the power supply lines) until you unplug it for awhile, and plug it back in.

A picture of my board:



What I've done:

1. Checked all the caps with an esr meter, they measure fine (but presumably could still be the issue with the below symptom?)

2. Tracked what is happening, but not the actual cause, down to the IC protection circuit (tea1530):

The voltage on the protect pin of the IC quickly goes up to about 2v, and then slowly increases to >2.5v at which time the IC latches into protection mode and will not resume operation until the Vcc drops below 4.5 volts (as per the datasheet, only will occur after removing the mains).

3. The longer the monitor is unplugged seems to effect how long it operates before shutting down. If it is only disconnected long enough to reset the IC operation, the protection hits 2.5v fairly quickly (seconds) after plugging it back in.

4. I have no idea what the protection circuit is doing or is meant to do

Thoughts? Should I just replace all the caps anyway?

[ben7]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

I've got a Dell U2311H, which will operate for some amount of time, and then turns off and becomes completely unresponsive (no LED, no voltage on the power supply lines) until you unplug it for awhile, and plug it back in.

A picture of my board:



What I've done:

1. Checked all the caps with an esr meter, they measure fine (but presumably could still be the issue with the below symptom?)

2. Tracked what is happening, but not the actual cause, down to the IC protection circuit (tea1530):

The voltage on the protect pin of the IC quickly goes up to about 2v, and then slowly increases to >2.5v at which time the IC latches into protection mode and will not resume operation until the Vcc drops below 4.5 volts (as per the datasheet, only will occur after removing the mains).

3. The longer the monitor is unplugged seems to effect how long it operates before shutting down. If it is only disconnected long enough to reset the IC operation, the protection hits 2.5v fairly quickly (seconds) after plugging it back in.

4. I have no idea what the protection circuit is doing or is meant to do

Thoughts? Should I just replace all the caps anyway?

Could we get a few more good pics of the board, particularly around that SMPS controller IC you mentioned? Be sure to get a few pics of the bottom side of the board too.

Yes indeed it does seem like something is wrong in the control circuit, but it is hard to tell if it is a bad capacitor.

Have you tried using the external power brick instead?

[Phinnegan]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Could we get a few more good pics of the board, particularly around that SMPS controller IC you mentioned? Be sure to get a few pics of the bottom side of the board too.

Yes indeed it does seem like something is wrong in the control circuit, but it is hard to tell if it is a bad capacitor.

Have you tried using the external power brick instead?

Sure thing, I'll take some more pics after my camera batteries charge - I'm not aware of any power brick for this monitor - I believe the socket there is for a speaker bar.

[Phinnegan]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Some more pictures http://brettb.net/dellmonitor/ - that large .22ohm resistor seems to have a bit of a surface defect, but it measures ok (.3-.4ohms, I only have a standard DMM which won't do low resistance, but that seems about right with the leads).

[ben7]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Some more pictures http://brettb.net/dellmonitor/ - that large .22ohm resistor seems to have a bit of a surface defect, but it measures ok (.3-.4ohms, I only have a standard DMM which won't do low resistance, but that seems about right with the leads).

Yeah it is probably OK.

My guess is a bad semiconductor, that is not working right when hot. Or a capacitor issue. Or a cracked solder joint.

About the DC jack, that seems weird though, because I have never seen them being used as a DC OUTPUT, not an INPUT!

[budm]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Dell monitor provides 12Vdc output jack to power the Dell soundbar powered speaker.

[Lumberjack777]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Definitely sounds like a heat related issue. The more it cools the longer it stays on, etc. I received a monitor that had the same problem awhile back. Somebody had previously "repaired" it by replacing the caps. But they lifted a pad and connected the cap lead to the closest component. But it wasn't soldered correctly; so when the board got hot and expanded very slightly, it broke the connection. Once cold, it would work again until the board expanded. I'm thinking those caps look just fine. Plus you tested them. It might be an IC or component breakdown due to heat. But. If you have some sort of magnification, you want to go over every solder connection and look for a small crack in the solder. You can also diagnose and isolate the bad area using a hair dryer to heat different parts of the board to see when it loses power. I learned that out here from budm. I'm thinking its possibly expansion of the board; causing a broken connection. At least that's where I'd start.

[Kiriakos GR]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Dell U2311H is very popular model in Greece, my own works well even with damaged USB hub due a USB stick which sorted out and possibly damaged the 5V supply.
I would appreciate a close-up picture of the PCB with the USB circuitry.

[Phinnegan]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Dell U2311H is very popular model in Greece, my own works well even with damaged USB hub due a USB stick which sorted out and possibly damaged the 5V supply.
I would appreciate a close-up picture of the PCB with the USB circuitry.

Sure thing, I added a few pics of the logic board to that gallery -> http://brettb.net/dellmonitor/.

[Phinnegan]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Definitely sounds like a heat related issue. The more it cools the longer it stays on, etc. I received a monitor that had the same problem awhile back. Somebody had previously "repaired" it by replacing the caps. But they lifted a pad and connected the cap lead to the closest component. But it wasn't soldered correctly; so when the board got hot and expanded very slightly, it broke the connection. Once cold, it would work again until the board expanded. I'm thinking those caps look just fine. Plus you tested them. It might be an IC or component breakdown due to heat. But. If you have some sort of magnification, you want to go over every solder connection and look for a small crack in the solder. You can also diagnose and isolate the bad area using a hair dryer to heat different parts of the board to see when it loses power. I learned that out here from budm. I'm thinking its possibly expansion of the board; causing a broken connection. At least that's where I'd start.

I did go over all the joints with a loupe, they all look great.

The kicker is, nothing really seems to even get hot, the issue still happens just the same with no load (i.e. the logic board and backlights unplugged). There will be correct 3/5/12v output for a bit, and then the IC just shuts it all down once that protect pin hits 2.5v.

I haven't tried the hair-dryer, but I'm pretty sure the issue is being caused by something around the IC, seeing as the issue occurs whether or not anything else is hooked up. I wonder if the mosfet could be acting up?

[Kiriakos GR]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Most protection circuits get activated when mA rising more than a specific limit.
Bad caps is the usual suspect due their ESR.
No one can say how perfect work you did on checking those capacitors.
My suggestion is to start over from the beginning, and unsolder every cap, let it cool for 2 min and then measure the ESR.

[Phinnegan]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Update: After much prodding with the multimeter, one of the zener diodes in the protection circuit seemed to be dropping less and less voltage over time, and the resistor in series with it was the one being monitored on the protect pin, so eventually there would be >2.5v across the resistor. I replaced the diode and it seems to be working ...so far... Of course that could have just been a symptom (the diode going wonky), time will tell.

[Kiriakos GR]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Zener diodes does not fall apart that easy, their upper functional temperature is up to 80C.
If you have a way to measure the temperature of this diode this could be a good evidence if the circuitry is really healthy.

[Rolito]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Update: After much prodding with the multimeter, one of the zener diodes in the protection circuit seemed to be dropping less and less voltage over time, and the resistor in series with it was the one being monitored on the protect pin, so eventually there would be >2.5v across the resistor. I replaced the diode and it seems to be working ...so far... Of course that could have just been a symptom (the diode going wonky), time will tell.



Dear Phinnegan,
I have replaced capacitors but still get the same problem as you.
Did you fix the monitor by replacing the zener diode ?
Could you tell me which is the protection pin and failing diode ?
Thanks

[GrahamJ]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Update: After much prodding with the multimeter, one of the zener diodes in the protection circuit seemed to be dropping less and less voltage over time, and the resistor in series with it was the one being monitored on the protect pin, so eventually there would be >2.5v across the resistor. I replaced the diode and it seems to be working ...so far... Of course that could have just been a symptom (the diode going wonky), time will tell.



Dear Phinnegan,
I have replaced capacitors but still get the same problem as you.
Did you fix the monitor by replacing the zener diode ?
Could you tell me which is the protection pin and failing diode ?
Thanks

Hi Rolito and Phinnegan,

My u2311H is also suffering a similar problem, was flicking various brightness levels for a few weeks and then eventually went to a state where it would only start up for 1 second and flash the DELL logo before turning off the backlight (power LED stays blue).

Ive also removed the powerboard and can see no capacitor bulging. I decided to order a second hand powersupply from Aliexpress (chinese seller) and it arrived here in Australia within about 2 weeks, unfortunately it seems to have the same problem although lasts about 2-3 seconds before it shuts down compared to 1 second on the old power supply.

From my limited tech knowledge Im guessing that there are only 2 Zener Diodes on this board which are the little orange components on the rear of the board marked on the circuit as ZD601 and ZD603? Each one appears to have a single blue band at one end and they are surface mounted, they are also glued to the board it seems so Im wondering how difficult they are to replace and whether the glue will melt when I heat it.

There is another diode that looks very similar at D801 but it has a black band and the fact that its missing the Z means its not a zener??

Hoping a few of us can get together to help sort out and repair these monitors, although surface mount soldering looks very fiddly and not sure if Im up for it with my limited soldering ability, are zener diodes easily damaged by heat if I take too long to solder them? Maybe it wouldnt cost too much to have an electronics tech replace a couple of them for me.

[selldoor]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Hi - couple of things strike me about this thread, firstly no-one seems to have considered the problem could lie on the main board. Heat also affects voltage regulators and if the one controlling the voltage on the pson , blon , or dim pins is going out then it would trigger the protection.

Secondly Grahamj I wonder if as you experienced flickering prior to an outright failure, then your problem may relate to lamps/wiring or inverters. May well be nothing to do with the power supply. Have you had the monitor from new - how long is that. Does/did the screen have a pink hue when it was on a white screen.
When the backlight has gone off does the on off remain responsive?
With a pc connected showing a known bright picture, if you shine a flashlight at an angle, can you see a very dark image of what the pc is showing.

If so you should read this if you havent already:
https://www.badcaps.net/forum/showthread.php?t=10419

start at post19

[GrahamJ]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Hi - couple of things strike me about this thread, firstly no-one seems to have considered the problem could lie on the main board. Heat also affects voltage regulators and if the one controlling the voltage on the pson , blon , or dim pins is going out then it would trigger the protection.

Secondly Grahamj I wonder if as you experienced flickering prior to an outright failure, then your problem may relate to lamps/wiring or inverters. May well be nothing to do with the power supply. Have you had the monitor from new - how long is that. Does/did the screen have a pink hue when it was on a white screen.
When the backlight has gone off does the on off remain responsive?
With a pc connected showing a known bright picture, if you shine a flashlight at an angle, can you see a very dark image of what the pc is showing.

If so you should read this if you havent already:
https://www.badcaps.net/forum/showthread.php?t=10419

start at post19

Thanks for your interest and the link to the diagnostic page, a lot of it looks beyond my skills but makes things clearer and should help.

After receiving my replacement powersupply (secondhand) I was thinking that perhaps the issue lays elsewhere as this replacement seems to suffer the same symptoms, however it does take slightly longer to "go to black" compared to the original one so Im not so sure. Being secondhand I really have no real way of knowing for sure if it was properly tested or what the problem was with the donor monitor (Ive asked the supplier but not sure how much they will be able to tell me as its a chinese seller and they may not know the history of the item). Wish I had a known good powersupply so I could tell for sure.

I have had the monitor since new (probably 3.5 years old now and daily use). In the last month or so before failing the monitor had been flicking brightness levels when waking from sleep, it would flick for an instant to a brighter level if I remember correctly then drop back in brightness, it would then stabilise. In the week prior to it failing completely it would do this randomly whilst the screen was on.

No noticeable pink hue prior to failure. Monitor is able to be switched on and off with the power switch at the front and will burst to life for an instant each time before switching to black.

I did try the torch test earlier today before I saw your message but was not able to see any LCD activity once the backlight went off, I think I will check that again though with an image that has more contrasting areas and see if that makes any difference.

So if I can see a shadow of the LCD image with a torch (but I dont think I can at this stage), what direction would that generally send me?

[selldoor]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

So if I can see a shadow of the LCD image with a torch (but I dont think I can at this stage), what direction would that generally send me?

Hey "Torch" in Oz - when you use that on a US thread they query what you mean.

It would send you to test the inverter transformers, then if they are ok try an
alternative bulb if you have one or build some test lamps - we have instructions.
Last would be to check out the bulb wires at the bulb ends and the ends of the bulbs. OR try these bulbs on another machine. Just depends what you have available.
If the connector between boards are labelled at either end can you take a close up pic of the labelling. eg 12v 5v gnd pson blon dim

Something else to try would be just swapping the bulb connectors from one socket to another
perhaps try the two at top to two at bottom.

Also can you post good clear pictures of the top and bottom of the power supply straight on without flash using manage attachments and I will look for cold joints and show you where to test the transformer

[cdrov]

Re: Dell U2311H, display turns off after some time, requires unplugging to reset

Does anyone has the schematics of the power supply?

Earlier someone mentioned some zeners... Can you please identify their type?