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Seems some QNAP models may or may not experience backplane issues die to the involved MOSFets not doing their work properly.
This here is a copy, just for my own purposes, based on info mostly posted in the QNAP Forum.
For me, the backplane issue reveals itself often on boot, seemingly when the system is still "warm" from running just a second ago. So far I've worked around like:
- Never shutdown teh NAS, at best go to sleep mode.
- Make sure you use UPS with your NAS, since power brownouts may kill the power supply and/or MOSFets.
Note: I have experienced this with my TVS-873 (which QNAP replaced for free) and my TS-896 Pro (I am using the sleep trick for now).
Based on Kommisar's post we gave it a shot today and it looks to be working.
Disk 3 is on, and raid is rebuilding.
If you are going to attempt this on your own boards, read and understand Kommisar's post so you can trace your own board.
Verify your problem is identical before trying this solution.
Here is what was needed for my specific scenario (disk 3 failure, eventually leading to no power).
The mosfet that seems to be the issue is on the opposite side, and is labelled 4957AGM. Google for pinouts (datasheet attached below).
That IC contains 2 mosfets.
Tracing the pins looks like one feeds the 12V sata pins and the other feeds the 5V sata pins (at least for bay 3, other bays may need a different fix).
Shorting the source and drain of each will bypass the mosfet and supply power permanently to the sata ports.
One or both could be faulty, in my case it looks like only the 5V fix was needed but we did both.
** You could also just replace the IC with another 4957AGM, although it may still fail again (something caused it to fail originally).
Shorted:
Make these changes at your own risk. Modifying a circuit should be your last resort! RMA it if you are not familiar with what is shown here (or don't have a friend who is!).
Might not hurt to ask QNAP support if they will offer up a replacement board for sale (it's an easy enough swap), assuming they have a solution to the fault.
Thanks Kommisar for the diagnostic work!
Note:
Some QNAP backplanes have jumpers to short the MOSFets.
You'll have to trace them to make sure yours has these jumpers and that they are indeed the right jumpers.
(source)
Datasheet:
This seems to be the same issue I'm facing with my TS-869 Pro. I looked into finding a replacement backplane but had no luck. Then, I thought about trying new SOP chips 10pieces AP4957AGM 4957AGM SOP-8 chipset - AliExpress 502, which are quite inexpensive. However, as you mentioned, "they’re failing for a reason," so maybe that’s not the best route.
Your post has been incredibly helpful—thank you! I’m considering bypassing all eight SOP chips unless there's a way to identify which ones are bad for certain.
One more question: I’m new to the platform, so where can I find the post by "the Kommisar" that you referred to?
Thanks again for your great work!
Just keep in mind that these MOSFETs have a legit function: powering up the disks in groups, so not all disks pull full power right at the start - the power supply may not be able to handle this. So bypassing them all is probably not a good idea.
Note: my 896 Pro has the same issue as well, on Occassion.
My fix: never shut the NAS fully down, just put it to sleep when not in use.
When doing that (sleep instead of power down) I have never seen this happen again.
My theory with my 869: when rebooting the system may already be "warm"? Cold boots, where the system has been off for several hours, have not given me any issues either.
** my 873 had much bigger problems and just became un-usable. QNAP replaced my unit for free at that time. Your (and mine) 869 won't qualify for that I'm afraid.
