DS918+ blue flashing LED, DOM suspected dead

[poseido]

Hello everyone,

I recently acquired a DS918+ in unknown condition. When it first arrived, it showed a flashing blue LED and both fans were running at low speed, indicating it wouldn’t boot. Suspecting a corrupted BIOS, I followed the  Unbrick Synology DS918+ https://forum.doozan.com/read.php?3,128079 (doozan) guide to flash a new BIOS. That seemed to bring the unit back to life—at least partially—but it still behaved erratically. Sometimes, after powering it off, it wouldn’t power on again. I’d have to wait a few minutes before trying, and then it might boot successfully. Other times, it was back to the flashing blue LED.

A couple of weeks ago, the NAS stopped responding on the network, so I rebooted it—and now it never moves past the flashing blue light. I started to suspect the DOM (Disk on Module) might be the real issue, and that my earlier success was just coincidental.

My first step was to try reading the DOM directly. I stripped a USB cable and connected the four wires to the DOM. However, Linux doesn’t recognize it (nothing appears in lsusb or lsblk), and Windows 11 reports that the device is defective and doesn’t show it in Disk Management. I’ve tried swapping the data+ and data– wires just in case, and I’ve checked continuity.

My current wiring is:

Pin 2 → +5V

Pin 4 → Data– (tried also swapping for data +)

Pin 6 → Data+ (tried also swapping for data -)

Pin 8 → GND

My questions are:

Am I wiring this incorrectly, or is my DOM truly dead if it’s not recognized by either OS?

Are there any other troubleshooting steps you recommend before concluding that the DOM is permanently damaged?