Solved The motherboard suddenly went black screen.

[lcldiy]

I disassembled two 7900X motherboards. Initially, everything worked fine. Then I desoldered the video cable using a soldering iron. After rebooting, the screen went black but sound was still present—audio functioned normally. The screen remained black, and the composite video signal also showed no image. Both motherboards exhibited the same issue. However, after cutting the board, everything worked properly again. After some time of use, the screen suddenly turned black once more, although sound continued to work. Could the video chip have been damaged by static electricity?

 

[Kowabungus]

If two boards are doing it I'd say try and first rule out the common denominators. What are you using to power them / what display are you using?
If able to provide some photos fully wired up that may also be helpful for us to look at!

Thinking unlikely in your case, but I've ran myself crazy before with a black screen only to realize I accidentally swapped video output settings at some point. Blindly swapping between them using the guide below is maybe worth a shot if you haven't already tried:

 

[lcldiy]

If two boards are doing it I'd say try and first rule out the common denominators. What are you using to power them / what display are you using?
If able to provide some photos fully wired up that may also be helpful for us to look at!

Thinking unlikely in your case, but I've ran myself crazy before with a black screen only to realize I accidentally swapped video output settings at some point. Blindly swapping between them using the guide below is maybe worth a shot if you haven't already tried:
View attachment 44098

Thank you. I also tested this, but there was no image. Is it that the graphics card is damaged and there's only sound?

 

[Kowabungus]

Thank you. I also tested this, but there was no image. Is it that the graphics card is damaged and there's only sound?

It could be a few different things, I don't immediately suspect dead gpu since two boards are experiencing it. I don't know for sure though without seeing how it was wired up.

What grit sandpaper did you sand up to? I usually go to at least 1000grit on all my trims
Also were the chips masked off before trimming/sanding? Copper dust can get under bga chips and cause some nasty problems too

 

[Luigid]

It might simply be shorted from when you redid the soldering; cutting the board right across those traces makes it easy to cause short circuits. You can use a multimeter to check if the various video signals are grounded. If you can hear the sound—meaning everything else is working fine—then it’s just an output issue; try tapping the signal from the positive terminal of the capacitor at point 6.

 

[lcldiy]

It could be a few different things, I don't immediately suspect dead gpu since two boards are experiencing it. I don't know for sure though without seeing how it was wired up.

What grit sandpaper did you sand up to? I usually go to at least 1000grit on all my trims
Also were the chips masked off before trimming/sanding? Copper dust can get under bga chips and cause some nasty problems too

View attachment 44099
It might simply be shorted from when you redid the soldering; cutting the board right across those traces makes it easy to cause short circuits. You can use a multimeter to check if the various video signals are grounded. If you can hear the sound—meaning everything else is working fine—then it’s just an output issue; try tapping the signal from the positive terminal of the capacitor at point 6.

Thank you for your assistance. The component has been successfully replaced with model CXM4015, and the system is now operating as expected. During troubleshooting, a counterfeit HAKKO electric soldering iron—manufactured in China—was identified as the root cause: it exhibited an ungrounded static voltage of approximately 90 V, resulting in electrostatic discharge (ESD) damage to the integrated circuit.

 

[Stitches]

Thank you for your assistance. The component has been successfully replaced with model CXM4015, and the system is now operating as expected. During troubleshooting, a counterfeit HAKKO electric soldering iron—manufactured in China—was identified as the root cause: it exhibited an ungrounded static voltage of approximately 90 V, resulting in electrostatic discharge (ESD) damage to the integrated circuit.

I also had one of those fake Hakko irons that killed things, but mine was Russian

 

[lcldiy]

I also had one of those fake Hakko irons that killed things, but mine was Russian

Russia does not produce this brand. hahaha

 

[Luigid]

Basically a soldering gun—it's strange that the chip was still responding to the I2C address, allowing the boot process to complete and the audio to work.

 

[lcldiy]

Basically a soldering gun—it's strange that the chip was still responding to the I2C address, allowing the boot process to complete and the audio to work.

Even if this chip is removed, the audio will still function properly.