[Solved - Power switch] 50D won't turn on, no sign of life

[X-RAY]

Hi,
I got a 50D... worked without issues, just changed the lens when powered off and it didn't power on again at all. No sign of life, no LED blinking.
Charged the batteries, put out the clock battery, changed lens and CF Card in many combinations, but it just doesnt do anything anymore. 
Any ideas or suggestions?
Is there a possibility for that model with diagnostic tools? I'm not sure if there are parts of magic lantern left in the firmware, I tried a bit with that camera a while ago. But the card is clean of ML.

[Walter Schulz]

Prepare card with EOScard (Windows) or MacBoot (macOS). Check card, delete all files and directories (but do not format). Copy portable display test autoexec.bin to card.
https://www.magiclantern.fm/forum/index.php?topic=2296.0

Remove battery, insert card. Insert battery.
You do not have to power up cam. Just close compartment door ...
Results?

[X-RAY]

Hey there,
thanks.
The download link from alex seems not to work at the moment, is it off? Also the bitbucket link https://bitbucket.org/hudson/magic-lantern/ is not available anymore.

When the card is bootable do I just need to put the autoexec on the card?

[Walter Schulz]

Just tested the link for Portable Display Test autoexec.bin and it is working.
Yes, for this particular test autoexec.bin should be sufficient.

[X-RAY]

I'm sorry, my Chrome has issues with the download, another browser worked fine.

Well, I inserted Card, then Battery and just closed the compartment. Waited a little, but nothing flashes etc.
On the computer I saw no new files on the card. Didn't seem to do anything.

/edit
doublechecked, the card is still bootable according to eoscard.

[Walter Schulz]

This test would work with cam's bootflag set.
If ML was uninstalled properly cam's bootflag is gone and this test won't work.

a1ex?

[a1ex]

You could test the card in another camera (signature suggests you've also got a 5D3). The same binary works on all cameras.

If the card is prepared correctly (bootable + portable autoexec.bin, confirmed working in another cam), and ML was running before the crash (boot flag enabled in camera ROM), lack of any kind of visible activity means... the problem is on the hardware side.

You could check the UART port for any kind of activity, if you feel comfortable with this step, but I don't have high hopes. Sorry.

[X-RAY]

Oh wow, it seemed that the card has issues.. because it didn't load anything in 5D3 either. I tried another card which is running ML in my 5D3 and the screen shows up ... also in the 50D! So what does that mean?
Some loading issues? Can I flash a firmware or something?

[Danne]

Simply use a fresh card. Why would you need to flash firmware if your card is strange?

[X-RAY]

Because, the camera still doesn't boot normally when I don't insert a card at all (nothing shows up or blinks). ;-)
The question is, what is wrong with the booting and how can I reset that state.

[a1ex]

Step 1: Portable ROM dumper. Send me the files privately.
Step 2: startup-log and startup-log-mpu. One of those might be able to save a log, or at least perform a LED blink.

If all else fails, UART would be the easiest way to diagnose it, but there are some other ways.

[X-RAY]

After a few insightful days and PMs with alex later (of course huge thanks to his help as always) I seem to have figured out the problem with this camera.
Perhaps its helpful for others with similar issues.

alex analyzed the logs and told me
Your ROM boots fine in QEMU, camera starts with main display off, menus in German. So, if there is anything wrong, it must be from the MPU (secondary CPU).
Possible suspect: the power button.

Well, I figured out that its pretty simple to get the backside of the 50D off (quiet similar at least to 40D and 5DII), there are helpful videos at youtube. You just have to unscrew 4 or 5 screws, one is under the grip-leather (pretty easy to peel it off). After that just 2 flex cables are connected to the camera.
Interesting behaviour was, that without the whole camera backside, the camera showed all the normal settings on the upper display when the battery is connected again. Also AutoFocus worked fine, but the camera didn't engage the shutter.
Also when I just connected one flex cable it behaved the same way. When the flex cable with the power-switch is connected it didn't start anymore.

So I had a closer look at the power switch. One component is the hardware-power-lever you see from the outside... but that thing is internally connected to a tiny switch on the inside that also has the 3 states "Off / ON / Locked".
Well, the problem is simply the tiny switch on the flex cable which failed or is broken. It doesn't spring back when the camera is Off and the power lever is turned back On.

To clarify here is an explanation-image:


With a tiny screwdriver I can switch the micro switch to on, leave it there, put the battery back in and the camera starts normal again, with LCD image and all the function buttons on the back. Hooray.
At that point its the simplest way to just leave the micro switch and power lever disconnected and the camera always "On" and just shut it On/Off by putting the battery in/out. The micro switch in the battery compartment is kinda my new power switch.
alex added
You'd have to power down the camera by opening the CF card door - which is a perfectly clean shutdown, btw.
Even more - with ML, opening the card door while leaving the power switch to "on" is actually the safest method to turn off the camera. That's because the camera no longer wakes up to read autoexec.bin whenever you want to remove the CF card.

My conclusion is ... no wonder that Canon changed the power-switch layout after the 5DII (which should be a somewhat professional camera). ;-) That tiny thing is an essential part of the camera and can affect it to stop working.

/edit
Thanks to Mike Tornado, the specific switch in question is a Panasonic ESE23J101.