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August 16th, 2023 09:44
XPS 13 7390 2-in-1, CMOS Battery fault, no CMOS battery inside?
Hello all!
I have a XPS 13 7390 2-in-1 here has a CMOS Battery fault. Everything is fine as long as you keep it charged but if the battery dies it will lose all BIOS settings including service tag and boots into maintenance mode until the service tag is re-entered (and it takes several minutes to get the laptop booted up when this happens).
"No problem" you say, "just open it up an replace the coin CMOS battery!" But there is no coin CMOS battery on this 2-in-1 model
I found this link about clearing the CMOS involving removal of the main battery:
Does this imply CMOS some how uses the main battery to save settings? If so perhaps a new main battery would fix the problem.
Any help would be much appreciated. CMOS battery is usually such a trivial issue but in this case it makes the laptop unreliable.
RoyBuckley
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August 30th, 2023 17:07
For anyone reading this in the future: You just need to replace the main battery.
There is something in the main battery related to the CMOS and the service tag. New battery installed (Dell original ordered from Dell Support) and no issue since.
ejn63
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August 16th, 2023 11:45
The system uses the main battery for storing CMOS information, but that should not include the service tag. The service tag should be written in EEPROM on the board that is nonvolatile memory.
If the system is booting into maintenance mode, there's something wrong with the system board itself.
RoyBuckley
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August 16th, 2023 21:42
@ejn63 ah ok so the eeprom must be faulty.
Is there a schematic available to identify this eeprom and I can try to de-solder, dump, flash a new one (on a GQ-4x4 or TL866) and replace?
By the way I'm typing from this laptop right now. No issues as long as the battery doesn't die.
(edited)
ejn63
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August 16th, 2023 22:22
You can probably find a schematic for purchase, but even if you do, schematics don't always have the level of detail you may need. And even if you do identify the chip and have the equipment necessary (hot air station) to remove and re-solder the chip, finding a replacement may be impossible short of buying a donor board that has failed for some other reason.
If you're going on a hunt, look around the area where the memory chips are soldered to the board. for an 8-legged device -- then cross reference the part number online to identify it definitively.