EOS 600D completely frozen with mirror locked-up

[snulkit]

Hi,

I have a Canon EOS600D with Magic Lantern for about a year and it worked always without problems.
Today, I wanted to do some filming. Lens attached is  a Canon EF 50mm 1:1.4.
As I was in movie mode, I changed the follow-focus setting in the ML menu.
From that moment, the LCD display turned out black and the camera didn't react anymore.
I turned it off but the mirror stayed in the locked position. Same thing for the diaphragm of the lens.
After that, I removed the battery and the memory card but nothing changed after reinserting the battery with or without the memory card.
I put another lens on the camera : nothing changed. The diaphragm of the 50mm lens remains closed event when detached from the camera.
I tried to restart the camera in all dial modes without succes.
Does anyone has another suggestion to unblock my camera? Is there an undocumented feature (key combination) to reset the camera?
Any help would be highly appreciated.

[barepixels]

there should be another battery (round flat one like for watches) to keep camera internal clock.  usually have to remove a screw to access it.  try googling that.

[Walter Schulz]

400D was the last 3-digit-D having this battery accessible.

[snulkit]

I can see the backup battery trough a small hole in the main battery compartiment but no screws to open it. Would this mean that the camera can be thrown away once the battery is dead? Can't believe this. There must be a way to access it. Does somebody has a service manual for this camera?

[dmilligan]

sounds like a hardware failure

try the blink test from here:
http://www.magiclantern.fm/forum/index.php?topic=2296.0

[a1ex]

If the mirror remains up after a crash, normally it is brought back down by the MPU (before loading the main firmware). Same for lens aperture - even if the main CPU is stuck, e.g. in the blinking test loop, the MPU is still running and will open the aperture. Since these don't happen, it may indicate a power failure.

The small battery only keeps the clock, no point in removing it.

Do you see any LED blinks or any activity in viewfinder? Tried another battery?