Samsung S32D850T powers off after some minutes, requires removal of mains power

[remaker]

I found https://www.eevblog.com/forum/repair/samsung-32-s32d850t-monitor-repair-story/ while searching for reasons why a dumpster-rescue monitor is failing.

https://www.eevblog.com/forum/profile/?u=495603 (@sausage) has been helpful through private communicaiton but I thought I'd ask more here. (Can you tag users on this forum?)

The unit works, but will power down at arbitrary times. Can be a few minutes, can be longer.

The PC announces that the monitor has been unplugged and reconfigures the displays as if it has been removed.

All panel buttons are inoperable.

Pulling mains power and waiting a few moments, it can power on again.

I hypothesize that the KF12N60F MOSFET is marginal, since that seems to be a common failure, so I ordered one, thought it will take a long time to arrive.

Any suggestions of interim things to try?

I chipped away the silicone (?) adhesive. I know some adhesives from distant past times, some adhesives have become conductive by breakdown or contamination over time. Is that a possibility here? I'm presuming not, but all that goop on the metal leads have me pause. I wonder why this part fails so often? Should I look for an upgraded part?

I also plan to use CPU grade heatsink compound on the reinstall.

I welcome any thoughts.

[hummerjanne]

Have you tested the KF12N60F MOSFET with a multimeter?
When you say all panel buttons, do they not work at all when turned on or off?
Have you checked the button connection or where it connects?

[remaker]

I replaced the KF12N60F MOSFET, which seems to be a problematic device in the power supply.

That did not fix the problem. Oh well.

To clarify the failure mode: The screen goes blank, all panel lights go off, the PC registers a disconnect of the monitor, and the panel is unresponsive. The only way to recover is to remove power from the monitor for 5-10 seconds and plug it back in.

The buttons all work fine when the unit has power and is not in this "crashed" mode.

The time between power off events does not seem to have a pattern to it.

[m k]

Since unplugging it is the thing, standby thingies may have a role.