Dell Monitor SE2416H turns off and then on automatically

[Tony.T]

I have a circuitboard from a Dell Monitor SE2416H

https://www.ebay.com/itm/263828211518

Everytime it has been turned on for a while it starts to shut down and on automatically. if i use a hot gun on some areas it turns off DIRECTLY.  (bottom right area on the picture from the link above).

i have tried to measure the changes in that area when it turns off but cant see anything odd.  it is hard to only warm up a very small area and as i said, the board turns off and on also without having to much heat on it. During normal usage . Only when powering it up it takes maybe one minute or two until the problem starts. it turns off and on every maybe 30-60 seconds. If i warm up the mcu itself it will turn off and on but it is hard to say if it is the mcu or some other components.

i measured the ps on/off connector and DIM. on the connector top left. two lowest pins.   And can clearly see that dim clock stops before the shotdown. THen on off pin  goes low aswell.  After 10 seconds the clock (dim) starts again and monitor turns on again.  Those leads go to the MCU tsum058cdt9-8

I can not find any pinout of this MCU to see what part of the circuitboard has this overtemp protection circuit.  Is in built in and the only right thing is to change the MCU or is it another part of the circuit that somehow is involved and that needs to be replaced.

The PS works good and all the voltages are present. And as i said....o can change the frequency of the turning off and on by heating it. Does not matter if it turns on after its shutdown...as soon i put the heatgun...it shuts off. (normally it does that again after 30-60 seconds but if only 2 seconds and putting the heatgun it shuts down)

Any ideas here? Any help?  Would be appreciated a lot.

[robert.rozee]

are you feeding it with a VGA or an HDMI signal, or no signal? if VGA, try HDMI and see if it makes any difference.


cheers,
rob   :-)

[Tony.T]

i.m feeding it with HDMI.

Will test VGA ASAP....

[wraper]

If this happens with menu switch PCB attached, I would suspect bad switches first.

[Tony.T]

you mean the physical buttons on the monitor attached?  It is connected directly to the Powersupply. the monitor does not turn on at all then.

I just tried to turn on the monitor again COLD.  And usually it takes 10 minutes until the problem occurs when it has cooled down for long period. Turned on the heating gun at 75 degrees Celsius and it shut down after 2 seconds when blowing on the bottom right corner.   have also used thermal camera to see if something gets warm by itself. Nothing at all.

[wraper]

Yes, physical buttons. It's a quite common problem with TACT switches becoming somewhat conductive. Remove power when monitor it turned on and disconnect them. Likely monitor will turn on automatically when you reconnect power.  If that does not work, disconnect them while monitor is working, and see if it fixes the problem.

[wraper]

Also why you say they are connected to PSU? There is an FFC connector on the main board where FFC from button board is connected.

[Tony.T]

Aaa..sorry.  i thought that you ment the other connecor...wires that goes from the corner of the monitor to the PSU.  That was what i thought you were talking about.

The one that you ment...the flat cable (FFC), was not connected at all to the motherboard when i tested.  Soo it cant be something with the buttons then. The behaviour is still the same. Only the large flatcable was connected and the the cables to the PSU from the motherboard.

[wraper]

Just in case still check if all buttons work as intended. Main PCB looks like it could be using resistor voltage divider for buttons. It's a way how to reduce I/O count. The issue is that when something goes wrong with resistance/voltage level buttons either stop working, act as another button or there are false positives.

[wraper]

As of acting on heating bottom right area, the only thing that's somewhat close and could cause that is U702 buck converter which is in the middle of the right side. Check if buck converter output voltage on the right side of L702 is stable and does not have some weird value.  What's on the bottom right quadrant should be completely irrelevant to the issue. As it's just input circuity for VGA and EDID EEPROM. Above U702 there is also an EEPROM and FLASH which I guess could be relevant to the issue.

[Tony.T]

New tests today.

Doesn´t matter if using VGA: same problem.

Measured buck converter....flash and eeprom ..nothing strange.   As soon heat is applied around the MCU...it shuts down instantly.   Should perhaps be easier to understand if i had the pinout or datasheet of this mcu. But cant find it at all.   MCU.... TSUMO58CDT9-8

See if it is easier to pinpoint exactly the component if using solder-iron to heat component by component...... 

[wraper]

It's not an MCU but display controller. If everything is fine with power rails, most likely it's bad. You could try replacing crystal just in case but I doubt it will help. If it's bad, I guess the only thing you could do is try mitigate the issue by attaching some heatsink on it.

[Tony.T]

I just tested to have a mini fan to cool down the display controller. put some heat on other parts of the circuitboard and it seems to work. When i put the fan on other parts and heat up the controller it stops.
So putting a fan would ofcourse work but it feels like cheating  :-).  But anyway, replacing the display controller i think would work as i think that the eeprom and flash is intact and replacing the controller would not need some kind of flashing it??   OR?  you seem to have a lot of knowledge here and i really appreciate your help/advices

The shortcut is of course just to add a fan. 5V i can get from the circuitboard. But i can get the controller for 10 euros...  but is it wasted money?

Having the datasheet would maybee give an answer, how does the temperature sensing work etc....  just for better knowledge:-)

[wraper]

Don't know anything about this one. It may have some firmware in it or may not. I just read some comments on aliexpress and it seems replacement works without flashing firmware. BTW this particular seller is known for selling good working parts, especially BGA computer chips in cases when there is a lot of faulty and relabeled garbage around https://www.aliexpress.com/item/32868484414.html

[Tony.T]

You are FANTASTIC ....thank you.  I will do some more experiments to see if there is some components around the controller that could somehow affect the whole thing but i think that the controller has an inbuilt temp functionality that goes wrong.  Maybe i´ll take a chance and exchange it...  :-)

[wraper]

More likely it's just faulty, crashes when heats up and watchdog restarts it.