I got a Mavic Mini from a friend to fix, but it’s only blinking the 4th LED, and I can’t find this error in any troubleshooting guide. I’m stuck. I was the first to open it, and the ribbon cables were still glued down. I used hot air to remove the glue, replaced the mainboard with a spare I bought, but the same issue persists. I even replaced the ESC, reset the battery, and tried a known working battery, but still the same problem. I’ve cleaned all ribbon cable connections with IPA and a soft brush and tried turning it on without the GPS and gimbal connected. I also desoldered the motor cables in case of a short, but no luck. I’m out of ideas. Any suggestions would be appreciated.
Doesn’t the 4th LED mean the battery is charged up to 25%?
It’s not the first LED (next to the button); it’s the fourth LED.
Ah, got it. Sorry!
That looks like the 1st LED blinking in your video, not the 4th.
You might be right, but I’ve tried two different full batteries and two different ESC boards, so it’s not a battery issue. It could be a power issue related to another component.
I’ve seen this happen with dead motherboards. Maybe your replacement motherboard is faulty too.
That’s why I don’t trust buying core boards online. They could be faulty, and you end up replacing other things unnecessarily, only to still have the same issue.
Exactly. It’s hard to find brand-new ones, and fixing drones feels like whack-a-mole. One time, I got a Mini 3 with the previous owner’s photos and videos still on it 
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Yeah, even dealers can’t get new ones. DJI has core boards locked down tight. Asking for photos helps, but unless you have a known working drone to test with, it’s tough.
Did your friend open the drone before you? It could be as simple as the ESC-to-core board flex cable being damaged. That cable is notoriously easy to break on the Mini series after a crash or over time. If someone opened the drone, even gently touching the cable can cause issues. Since you’ve replaced the core board and ESC, the cable might be the last thing to check. What was the original issue? Was it in a crash or just stopped working one day?
Thanks for replying. It had water damage but wasn’t submerged. It touched the water and then flew back. After that, it stopped charging via USB, but it still had video feed and could fly. Now, it won’t turn on at all. I’ve replaced the parts I mentioned, but if the flex cable is that sensitive, it could be the issue. I was careful when opening the drone, though—I used a reflow station and applied 150°C to remove the hot glue from the connectors.
Water damage is tricky because new issues can pop up over time. I noticed in your video that you’re not turning the drone on correctly. Are you familiar with DJI products? Usually, an ESC or cable issue is indicated by the middle two LEDs blinking.
No matter how long I press the button, it won’t turn on. It just blinks when I do a short press, even with a full battery.
A short press only shows the battery charge level. Batteries discharge automatically over time, so it could’ve depleted since then. The lights seem to be behaving normally.
By the way, are you sure you’re turning it on correctly? DJI drones usually need a short press followed by a long press (about 3 seconds) to turn on. A single press won’t power it up.
The battery is fully charged, but it still doesn’t turn on with a long press. It just blinks with a short press.
To turn it on, you need to press, release, then press and hold. Think of it like ‘beep, silence, beeeeeeeep.’