Basically I think it's the same issue as the 100 Ohm resistor rework for the Synology, except pulling it to ground. If you look at this video (
https://youtu.be/Y8_emfoR_MI?t=853 ), maybe the p-channel is bad/shorted in the Qnap while the n-channel is bad/shorted in the synology case. Regardless, if you still have the dead Qnap, there's no risk for trying it out. Don't PM me for this, except if you want to pay for my remote consultation or build up your confidence, I can certainly entertain that. But really the summary in the link below should contain everything you need to know for the rework. Also according to the comment in that video, some reported it works for years after the rework and some reported the system died after 6 months, so don't count this as a way to get a cheap NAS, as YMMV. I would recommend to turn it on only when you need to use it even if you don't have the problem currently or it works again after the rework. If you plan to buy used systems, look up the CPU first and avoid all these models, including the Synology. With the temperature gets colder, I felt I ran into more boot failures. Also saw this https://youtu.be/c5k8FWe6u60 after I posted this. Apparently he went through the same debug couple months earlier than me and recorded his finding as well.
QNAP TS-453 Pro stuck on "SYSTEM BOOTING"
Note 1:Scope or measure the LPC-CN1(10-pin connector, next to 4-pin COM1 connector), pin 1 (LPC CLK, normal ~1.7V)
If the voltage is > 2.2V, solder 100 Ohm (or 80~350 Ohm) between pin 1 (LPC CLK) and ground (pin 8 or 10).
If the voltage is < 1V, solder 100 Ohm to a 3.3V pin(since this does not apply to me, someone as would have to spend time to find it). Also read the "Note #1" below.
If you still do not see a correct system temp/fan speed, try a lower resistor value, like 80~95 Ohm.
Soldering a header to it (or just the 2 pins) might be a good idea, since you can swap out different values easily when needed (or when it failed again).
Some reported for the LPC_CLK < 1V systems, they can still be recovered by lowering the voltage of the clock further. It's contrary to the assumption above, based on the Synology failure. My guess is that the low of the clock is much higher on those systems, see the scope captured by mdudek in the link below. By pulling down further, that makes the low of the LPC clock recognizable by the system again.
Also the early symptoms of this issue could exhibit as long boot time (13 min vs 5 min in a normal boot with a clean install), missing drive bay(s) - at least confirmed on the TS-251(+), plus "0°C/0°F" System Temperature and "4294967..." RPM Sys Fan speed (failed LPC to the SIO). You can confirm the failure by using a coreboot tool (https://www.coreboot.org/Superiotool), superiotool to dump the SIO configuration. There're many posts that seem to have done incorrect multimeter measurements on this "DC" signal here. I did a quick search on the youtube to find one that provides a quick tutorial on using the multimeter. Hope this will help some folks here.