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Samsung 32" S32D850T Monitor Repair story
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m k:
Seems to be a bad connection when flipping a board is changing things, but is it supply chain or something smaller.
Is there any life after it goes off?

Old monitors had no default geometry, so OSD piggypacked incoming signal.
Newer ones have and small "no signal" rectangle or something similar is present even without input signal.

An internal control signal may be a single edge instead of a level.
So when something else goes wrong for a moment the situation is not recovering before that edge is recreated.

Since removing power cord is resetting the issue it must do something that other things can't.
This indicates that standby circuitry/functionality has something to do with it.
Maybe there is a rising edge of PowerGood.

If possible, measure how much current it takes.
There used to be models that consumed almost the same all the time, maybe that is in the past.
0xG1L:
Thanks for the answer.

When it shuts off, its totally dead - power led turns off, nothing responds, and there is no "no signal" sign.

I have also noticed that if I wait long enough (a few minutes) it comes back to life until it shuts off again.
I connected the main power through energy meter -
when monitor is in standby mode (when there's no video signal), or even when its turned of manually - power consumption is 0.2 watts steadily.
when the monitor shuts off by itself, power consumption drops to 0 watts for a few seconds and then it moves between 0 to 0.3 watts repeatedly.

Does this information help focusing on the problematic component ?

Thanks
madires:
Yesterday I fixed a Belinea (BenQ inside) computer monitor which didn't turn on anymore. Everyone would guess it must be the SMPSU. No, SMPSU is fine. Turns out it's the PCB strip with the push buttons. It has three pairs of mini push buttons, each pair shares one signal line, one push button shorts the line to ground via a 1k resistor and the other one via a 10k. One push button became conductive, around 5k when not pressed. That screwed up the MCU's button scanning causing the power on/off button to be ignored. All I had to do was to replace that bad push button.
Veteran68:

--- Quote from: madires on January 16, 2024, 03:02:56 pm ---Yesterday I fixed a Belinea (BenQ inside) computer monitor which didn't turn on anymore. Everyone would guess it must be the SMPSU. No, SMPSU is fine. Turns out it's the PCB strip with the push buttons. It has three pairs of mini push buttons, each pair shares one signal line, one push button shorts the line to ground via a 1k resistor and the other one via a 10k. One push button became conductive, around 5k when not pressed. That screwed up the MCU's button scanning causing the power on/off button to be ignored. All I had to do was to replace that bad push button.

--- End quote ---

Interesting that you mention this. My son-in-law gave me his old 32" FHD monitor that "died" on him, just because I was curious if I could fix it before we tossed it out. I disassembled it and checked the SMPS and it was fine, the 12V output voltages to the control board and both 24V backlight inverter voltages were present. But the power button wouldn't do anything. I confirmed the power button was making contact when pressed, but didn't check the other buttons on the PCB strip. When the obvious didn't pan out, I got busy with other stuff and set it aside for a rainy day. Now you've got me wanting to go back and check those other buttons.
m k:

--- Quote from: 0xG1L on January 16, 2024, 02:12:03 pm ---Does this information help focusing on the problematic component ?


--- End quote ---

Hardly a component, but maybe something.

Since it is restarting the fault is obviously not resetting its status, but consumed watts are very low.

If 0 watts is real there can't be any real higher leftover or memorized states.
Only thing that can have a sort of memory is a stand-by circuitry.

If power button is stuck and is constantly powering the thing there shouldn't be any stand-by possibilities.
For all normal situations power LED should also remain on.

Is there a setting how monitor behaves after power outage?
Setting that to stay off will reveal how power is actually going off internally.
If after that setting the monitor is still turning on the power is not really going off internally.

Power LED is many times connected to stand-by circuitry.
Measured wattage is also indicating that it's a stand-by circuitry that is acting up.

Is there any life in power LED when fault is on?
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