Phantom 2 Vision Plus CV310 gimbal top board red light issue

[fadetonoir]

I have a DJI Phantom 2 Vision Plus drone where the camera gimbal shows a steady red light immediately upon power on. According to the manual this is a "Critical error" but I can't find any more information about what can cause it, or anyone who has fixed it before without sending the drone to DJI.

When connecting to the drone via the mobile app there is no data from the drone - no FPV/black screen and no telemetry or other data whatsoever. The drone is otherwise working fine and I have stripped it down to check the cables leading to the gimbal (all are undamaged, and all pins have been tested for continuity with a multimeter), which suggests that the issue is with the CV310 gimbal top board (v4 in this case). The board has no apparent physical damage, which leads me to suspect a firmware issue, such as a failed update.

I have tried reflashing firmware using the standard update procedure by putting the file for the latest version on a micro SD card, inserting it into the gimbal and powering on the drone, but this has no effect - the board just powers on to a steady red light on the front, and one flashing slowly on the back (which wasn't visible before disassembly). Also, if I connect the board to a PC with a micro USB cable it is not detected at all.

I have repaired a few of these drones, and a few non-Plus versions as well, when they have had the no-FPV issue caused by a bad firmware update on the live view encoder boards, and even though this is a different issue I was wondering if it would be possible to connect to this board via UART and reflash the firmware. Searching for information on that led me to this repository, but I will admit that even though I've spent some time looking through everything here, most of it is over my head - I do board level repairs and have relatively little knowledge when it comes to firmware. So forgive me if this is the wrong place to ask, but this is the only place I could find information about this board so hopefully someone here could help me fix this, or at least rule out firmware as the cause of the issue.

My specific questions are -

Is anyone familiar with this specific issue on this drone/board and know what the possible cause(s) and fix(es) is/are? Can anyone tell me how to connect to this board via UART to reflash the firmware or get some sort of boot log from it? The page for the board (linked above) states "Some schematics were made by enthusiasts; links are TODO" - can anyone send me these schematics?