Z390 Taichi Unable to boot

Further information: The 4 pin power connector at the CPU is disconnected due to the PSU however this shouldn't be an issue given the CPU is completely stock.

Power supply is tested to be working in another system, I'm starting to fear a DOA mobo, is there any way to isolate this or the CPU?

About a month ago I purchased a Z390 Tachi and installed an Intel i3-9100 CPU and a pair of Crucial Ballistix DDR4-2666 8GB memory sticks. I'm using a Silverstone ST30SF 300 watt power supply that lacks the 8pin (ATX12V1) connector that the Tachi utilizes. Per the Tachi manual, with that power supply I was able to fully populate the ATXPWR1 (8) connector, the ATX12V2 (1) connector, and four pins (the pin 1/5 side) of the ATX12V1 (2) connector. Everything has been running well with three hard drives and onboard graphics. Booting from USB thumb drives hasn't been a problem either.

Since you seem to be having some random luck getting the system to start I doubt it is a power supply problem, unless the power supply is experiencing an issue with voltage regulation where one of the voltages is marginal or electrically noisy. Memory compatibility also seems to be an issue with some ASRock motherboards that I have used, and that certainly can lead to all sorts of stability issues.

ASRock support always seems to suggest clearing the cmos bios configuration, which is rather easy to do on the Tachi. There is a small push button (18) by the I/O panel that will clear the cmos. That might be worth a try since it won't cost anything.

You seem to feel confident that power and memory aren't the issue so, like member RLGL mentioned, probably trying a different CPU would be the next step. If you don't have a compatible CPU handy you might try purchasing another CPU. Most retailers offer a 30 day return policy, but check before making the purchase. Or you can purchase a cheaper CPU, like an Intel G4900 for around $60.

If you live near a Micro Center (here in the USA), for $25 they will test your components to help isolate the problem. At least that is a service offered by the Micro Center near me. I'd call and ask first if you opt for that option.

One other thing you might check, but might the CPU be overheating? Did you get a good smear of heatsink compound between the CPU and the heatsink? If there isn't a good thermal connection between the CPU and the heatsink I would imagine hotspots could develop and that could cause random crashes.

Anyway, I wish you luck with your troubleshooting.

A late nighter, I've been there and done that a few times. Glad to read that you had some success with the add-on graphics card.

The video gpu is actually onboard the Intel i7-9700k CPU and not part of the Z390 chipset. The motherboard will often have some signal level shifting or driver circuitry to support the video from the CPU, but usually that circuitry is rather incidental.

I can't say that I know what the Tachi has for video support circuity. It seems like it will still be difficult to determine if the problem is with the i7-9700K or the ASRock Tachi without swapping out one of those components.

Now that you have things running you might want to try using the Intel Processor Diagnostics Tool to see if it might be able to diagnose a problem with the UHD Graphics 630 GPU. I've never had the need to use it, but you might want to give it a try before making any new purchases or starting any RMAs.

https://downloadcenter.intel.com/download/19792/Intel-Processor-Diagnostic-Tool

https://www.thewindowsclub.com/intel-processor-diagnostics-tool

I'm not really into the whole multimedia experience. I'm usually happy whenever I see the display illuminate with a picture at boot-up. I can't comment on the 4K capabilities of the integrated Intel UHD Graphics 630 GPU but, according to the specs of the Intel i7-9700K, it does support 4k. The DisplayPort should be capable of providing 4096x2304@60Hz and the HDMI port 4096x2304@24Hz. I would think that should be sufficient to get a picture and have a computer that does not exhibit odd behavior.

It seems to me that the complexity of those two video interfaces can sometimes be fraught with display compatibility issues. Even the quality of the video cable can become a factor in whether a picture is displayed. Those times I have booted my computer using the HDMI interface, only to be met with a blank display, often left me yearning for the ease and reliability of the old 15-pin VGA video interface.

I assume you are using the latest Intel UHD 630 driver and the latest ASRock Tachi BIOS. Keeping everything updated with the latest firmware and software drivers is important. I can confirm that it was an eventual ASRock BIOS update that finally solved a frustrating HDMI problem I once had with another ASRock motherboard.

One last suggestion, as remote as this possibility might be, the Intel UHD 630 GPU must use a portion of the Corsair memory to function. An add-on graphics card has onboard memory and does not require the use of system memory to function. If you haven't done so already, it might be worth performing a memory test to see if any problems can be detected. Since you have 16GB of memory a thorough test will take many hours to complete. Windows 10 has a built-in memory diagnostics test, or you can use a program like memtest86.

I'm afraid those are the last of my suggestions. The only other option that I can see would be to go the route of exercising the process of elimination by swapping-out each component until you discover the culprit. Good luck.