UNSOLVED
XPS16 9640 - strange BIOS behaviour AHCI vs. RAID
Hi there, I am having a strange issue with - The BIOS setting for SATA/NVMe operation AHCI vs. RAID in AHCI the bios sees disks up to 1TB only and in RAID although it sees larger disks e.g. 4TB installed I keep getting regular System-diagnostic lights with the follow pattern:
| amber 3 | White 5 | Power-rail failure |
The system powers up and seems to work fine but the diagnostic light sequence keeps flashing. Restart and holding the powerbutton for 20+ seconds during the reboot clears the error. but seemingly upon wake from sleep the diagnostic lights flash again...
ANY advice or insights to fix this issue would be appreciated.
Thanks!
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Posted September 30th, 2026 22:16
Hi
There is a possibility that the power drawn is too much?
A memory module or storage module just taking a tad more then it should.
If possible try and run with less ram modules initially.
Kind Regards
anne_droid
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Posted October 1st, 2026 04:03
@Tesla1856 thanks - will try that and revert!
Is it normal for the BIOS to in AHCI mode not see disks larger than 1 TB?
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Posted October 1st, 2026 04:03
@anne_droid thanks - problem is that the ram modules are soldered onto the board...
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Posted October 1st, 2026 14:21
Dell Rockstar
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Posted October 1st, 2026 20:11
@Tesla1856 - Any idea on how to fix that please?
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Posted October 1st, 2026 23:30
@AllbirdF ,
@Tesla1856 - Any idea on how to fix that please?
Sounds like maybe your drives are not initialized as GPT. You can verify the type in DiskPart and other places.
Try "DiskPart Cleaning" them first.
Then when next accessed with Disk Management, be sure to select GPT (not MBR). Pretty sure that Initialization-type gets written. I don't think you even need a partition created.
(edited)
Dell Rockstar
Microsoft Windows and Apple iOS Developer (Retired)
- Like many of you, I can appreciate a good game-engine.
- I answer questions here, but I'm not a Dell employee.
- Consider giving posts you like a "thumbs-up"
- Posting models-numbers and software versions speeds trouble-shooting.
- Click "Mark as Accepted Answer" on any post that answers your question best.10
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Posted October 2nd, 2026 15:27
The recurring 3 amber / 5 white code seems worth investigating separately from the drive capacity issue. Dell’s manual identifies that pattern as a power-rail failure.
Does it also happen after waking from sleep with the original SSD installed? That comparison would help establish whether the replacement drive is involved. Running Dell’s preboot diagnostics and noting any error code would also give support something concrete to investigate.
Before trying DiskPart clean, make sure the drive is backed up—it removes the partition information.
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Posted October 3rd, 2026 09:59
That amber 3 / white 5 pattern pointing at a power rail while the system runs fine otherwise is odd — since a 20-second power-button hold clears it, this smells more like a BIOS/EC state bug than actual hardware failure. I'd try Tesla1856's suggestion first: DiskPart clean and re-initialize the drive as GPT, because a leftover MBR layout can absolutely confuse AHCI-mode disk detection on these boards. If the light pattern persists after a clean GPT setup, it's worth logging with Dell support since it's still under the behavior they should fix in a BIOS update.
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Posted October 3rd, 2026 12:06
Hi All, thank you for the input and advice here - it is greatly appreciated. I have set a new drive as GPT and did a clean install / setup - will see what it does now...
Tesla1856
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Posted September 30th, 2026 20:43
Dell Rockstar
Microsoft Windows and Apple iOS Developer (Retired)
- Like many of you, I can appreciate a good game-engine.
- I answer questions here, but I'm not a Dell employee.
- Consider giving posts you like a "thumbs-up"
- Posting models-numbers and software versions speeds trouble-shooting.
- Click "Mark as Accepted Answer" on any post that answers your question best.