Dell Latitude 7420 stop working after ec reset

Question

Context: my Latitude 7420 2 in 1 started to act weird after I disconnected the battery to do something on the laptop. Tablet mode stopped working unless fully flipped at 360°, and auto rotation was completely missing in Windows. After that it started freezing randomly while using it (mouse and everything would freeze on screen and a forced reboot was required when it did that) and sometimes I needed to power it on and off life 5 times before it actually boot. I decided to do a full ec reset (unplug the battery, hold the power button for 60 seconds, leave the battery unplugged for 30 minutes and then plug it back in), and now the laptop doesn't work at all. When I power it on, it goes to the Dell logo and freezes there. I can't acces BIOS or F12 boot menu. Nothing works. The fan spins up and the cpu heats up, but nothing just the dell logo. I read that all these issues I have coule be related to a battery reaching its end of life (and mine is indeed almost dead), but that freeze at the dell logo I don't think it's due to the battery I'm scared this is a dead motherboard. I need to fix this asap because this is my school laptop even tho I do have some time rn because it is the holidays, and Idk what to do right now to fix it. Could this be because of the battery? Or is it the motherboard? Also, I'm not able to get in contact with Dell at all, and this Laptop is not under warranty anymore.

LSUFAN51 · Accepted Answer

According to the System-diagnostic lights in your service manual, three amber, three white mean BIOS Recovery image not found. The solution is to flash BIOS to latest or replace mainboard.

Latitude 7420/Latitude 7420 2-in-1 Service Manual | Dell US

Please view the information in link below, hopefully it will be a help to you. Good luck.

Recover BIOS on Dell Computer or Tablet After Boot or POST Failure | Dell US

LSUFAN51 · Answer

I know some people wait until Dell logo to appear to start tapping F12 or F2 key, if this you, power off computer, power on computer, quickly start tapping F12 key continuously until you see Dell Preboot menu.

Please don't wait till Dell logo to appear to start tapping, soon as computer come on, start tapping F12 key.

If the above step doesn't work, please run Real-time Clock (RTC Reset) by following steps in link below:

Latitude 7420/Latitude 7420 2-in-1 Service Manual | Dell US

Also, if your computer is showing a pattern of blinking lights then check System-Diagnostic Lights in your computer service manual.

user_90f87c · Answer

@LSUFAN51​ Nope none of this worked. Also there's no blinking led pattern

anne_droid · Answer

Hi

https://www.dell.com/support/contents/en-uk/article/product-support/self-support-knowledgebase/fix-common-issues/no-post

AND

Open the bottom cover (if you are comfortable doing this):
- Disconnect the main battery first, then AC.
- Disconnect:
  - SSD
  - WWAN card (if present)
  - Any secondary devices (smart card reader, etc.).
- Leave only:
  - System board
  - CPU (soldered)
  - One RAM module (if your 7420 has replaceable RAM; some are soldered)
  - Internal keyboard.
With battery still disconnected:
- Plug AC in and power on.
- Watch for:
  - Keyboard backlight flash.
  - Power/charge LED blink sequence.
  - Any display flicker / Dell logo.

If in doubt please ask.

user_90f87c · Answer

@anne_droid​ tried that and the led only blinked once white. That's it.

ejn63 · Answer

If the system won't power up on AC only (with the battery disconnected), it's a bad mainboard.

If you are the owner and need to repair the system, the boards are only about $250 -- any board-level repair shop will charge more than that, and that's if it's repairable at all.

https://www.parts-people.com/index.php?action=item&id=39065

user_90f87c · Answer

@ejn63​ i tried unplugging all the accessories again and this time I got a 3 amber, 3 white error code

user_90f87c · Answer

@LSUFAN51​ Thanks. Since nothing worked, I guess I will look into replacing the motherboard

Latitude

Dell Latitude 7420 stop working after ec reset

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