Question ASUS ROG Strix Z590-A died while powered off?

[Bill Sudbrink]

I've had the following system for the past two years:

ASUS ROG Strix Z590-A
Intel I9-10850K
16GB Corsair DDR4 3200 RAM
RX6500XT graphics board
4 TB WD SATA disk
1 TB M2 SSD (added later)
Generic DVD drive

The machine has been on most of the time, plugged into an APC UPS. It was used mostly for video processing and an occasional game. A few weeks ago, I shut it down, along with most of the other computers in my basement, because I was trying to listen for a problem in a vintage computer that I was servicing. When I solved the problem, I powered up some of the computers, but I left the Z590 off because I didn't really need it for anything at that moment. For one reason or another, it has stayed off for the last three weeks.

I tried to power it up on Saturday and nothing. Absolutely nothing, no lights, no fans, no beeps. I've taken it down from the shelf it was on, next to two other computers that have been (and still are) running for the whole time and that it shares a KVM switch with. I tested the power supply with a commercial tester and with my own instruments, VOM and a scope. It looks ok. I shorted the CLRTC (clear CMOS) jumper per the manual. I tested the power switch and the reset switch, they both short when pressed and at no other time. I removed everything except the CPU and fan. I have just finally removed and reseated the CPU. No Joy. I also replaced the CR2032 battery although it showed good.

It shows two signs of life:
1) If you turn it on (power supply switch on the back) with the 24pin power plugged in but the not the 8pin power, you get the red LED as per the manual.
2) If you turn it on (power supply switch on the back) with both of the power plugs and nothing but the CPU installed and leave it long enough, the "accent" LED on the heat sink that covers the back panel connectors will come on and fast blink.
That's it.

Unfortunately, The other modern computers around here are either Ivy Bridge generation or AMD, so I don't have systems to swap parts with. I can't imagine what happened to kill it while it was off and didn't clobber its neighbors. I guess I will buy another Z590 chipset motherboard as a first shot at getting it back up. If it turns out that the CPU is toast...

Anyway, I welcome any ideas. Thanks.

 

[dwd999]

Random thoughts: is this a damp basement where the computer being off for weeks and cooled down may have corroded something? What kind of temperature and humidity do the computers experience in your basement environment? Could you at least swap out a power supply from one of your other computers?

 

[Bill Sudbrink]

Thanks for the reply. To answer your random thoughts first...
1) If anything it is a bit dry down here. The basement is walk out. The Z590 is in my lab/workshop which is pretty well grounded and static controlled. Static resist carpet, grounded mats on all of the benches and it was actually sitting on a grounded metal Hergo open frame shelf. Temp stays between 65 and 75 year round.
2) Yes, even though I was pretty confident in my power supply test, I went ahead and swapped with another PC. Results were the same except that the "accent" light immediately went into its "pretty" mode. Fading from color to color. Otherwise, still no beeps, LEDs, fans...

Now the interesting (unfortunate) new twist. As I swapped the power supplies back and forth a couple of times, I forgot to install the 8pin ATX_12V_1 power cable. I noticed the red LED just as I pressed the power switch and... the fans came on. There were still no LEDs other than the warning LED and no beeps or other life. This prompted me to examine the power supply cables. This was the problem:

The motherboard calls for pins like this:

+12 +12 +12 +12
GND GND GND GND

The "replacement test" power supply has the same, but the original power supply has pins like this:

GND +12 +12 +12
GND GND GND GND

At first, I thought "Well, it just wasn't getting as much current as it wanted". Followed by "How did this ever work? The PS 12 volt rail was shorted to ground!". Then I realized that the +12 pins must be somehow isolated from each other and the grounded +12 pin was in some way connected via a component (resistor? capacitor?) to a power rail. That component finally "gave up the ghost" in a way somehow related to the extended down time. Now the +12 rail is really shorted to ground on that connector so neither PS will come up if that connector is attached. All of the components on that area of the board are covered by heat sinks and trim pieces, so I can't see if something burned up or exploded (I don't smell anything). I hope that all of the other components (CPU, memory, etc) survived. I'm not going to bother to try to fix it. I can get a replacement Z590 board from Amazon, delivered tomorrow, for a little more than a hundred bucks. Oh! And I guess I'll get another power supply too.