Question Asus Z270I mainboard no power

[Novgorod]

I want to troubleshoot an Asus ROG Strix Z270I mini ITX mainboard that won't power on. It could've been water damaged but there is no obvious corrosion or burnt components. The orange standby LED (SB_PWR) is on but shorting the power button pins does nothing - the board doesn't even turn on the PSU, so the diagnostic LEDs won't help because they're all off without main power. This is what I checked so far:

• The PSU is good and turns on when manually bridging the pwr_on pin to ground in the 24-pin ATX plug.
• The power button header on the mainboard has 3.3V on one pin (ground on the other), so at least some of the standby circuit must be working.
• Forcing the PSU on manually (see first point) while it's plugged into the board doesn't start the boot sequence (no diagnostic LEDs turn on).
• The BIOS battery was flat (2.4V) - I replaced it but it didn't change anything (nor should it). That also means the BIOS settings were reset without making a difference.
• I removed everything from the board and tried to get it to turn on completely barebone (no CPU, no RAM, no drives) - only with the 24-pin and 8-pin power plugs connected, but same result. The board should at least turn on the PSU and get stuck at some boot error (CPU/RAM or so) with no components installed, right?

What else can I do to troubleshoot? Which component is most likely to prevent powering on the PSU from standby power? I guess it must be the EC or maybe some intermediate power rail. Is there a way to test it? If the EC is fried, then there's nothing left to do, but the hope is that it might be something small. It's probably not worth fixing such an old board, but it's virtually impossible to get a replacement for that CPU generation in that form factor - the used market for it is virtually non-existent..

In case it's relevant, the other components are an Intel 6700K with a water block, 2x16GB DDR4 RAM (don't remember the model) and some Samsung SSD. If the mainboard can't be saved, I'd also have to change the CPU turning it into an expensive upgrade...

 

[Lutfij]

Welcome to the forums, newcomer!

an Intel 6700K with a water block
Waterblock as in an AIO or an actual waterblock for a watercooling system? If the former, try and work with an air cooler with it resting on your CPU's IHS, meaning you breadboard the parts. Since you're dealing with a K SKU processor, you should be able to fire up the build with one stick of ram, and the iGPU without any storage attached.

You've generically listed your specs, please list them like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

From my experience, that board needs to be RMA'd if you're under the warranty period(assuming you purchased it) but the board needs replacing. If you need an mitx board, there are multiple options out there, that are far cheaper than a full blown platform upgrade.

 

[Novgorod]

Waterblock as in an AIO or an actual waterblock for a watercooling system? If the former, try and work with an air cooler with it resting on your CPU's IHS, meaning you breadboard the parts. Since you're dealing with a K SKU processor, you should be able to fire up the build with one stick of ram, and the iGPU without any storage attached.

Custom watercooling loop. I "breadboarded" everything already as breaded as it can possibly get - just the mainboard with nothing on it and it doesn't turn on the PSU all by itself. With minimal parts installed (CPU + 1 RAM stick) it doesn't turn on either, of course.

It's obvious that the board is faulty because it doesn't turn on by itself with no components installed, so the rest of the system doesn't matter at this point. All I want to ask is what would be the further steps for diagnosing which part of the mainboard failed - if it's the EC, then it's game over, but if it's some simple voltage regulator circuit, it may be fixable. The board is 6 or 7 years old, so there's no more RMA and it's long gone into oblivion on the used market.