VKB-SIM

My VKB MCG Pro v2 started to occassionally show erratic behavior of some buttons, so I downloaded the latest VKBDevCfg-C and firmware, flashed the stick and re-calibrated it. When I then tried to upload the joystick profile again, it turned off and now the black box (black version, "BlackBox_Main_v2_1" written on PCB) shows no lights.
I tried other USB ports, reboots and connecting the black box with the "Sys" button pressed, all to no avail. Is there anything else I can try or is the BB dead?
I also have a SGC v2 with which I did the same procedure and it worked. Can I connect the MCG to the SGC black box for testing?

Yes you can try.

When I connect it to the other black box, the lights turn on (blue on one side, blinking red and solid green on the other) and DevCfg shows it as Space Gunfighter. So it seems to be a problem with the MCG's black box.
Is there anything I can do to get the black box working again? I opened the black box, no visible damage to the PCB. Since all lights are off, I suspect it could be something with its power supply. Is there an alternate way to power it by the BB's BUS Power Selector?

Try plugging only the Black Box to USB, no base attached. Change the USB cable too. If still dead, unplug, press the button on BB and plug back to USB while still holding the button pressed; release after 10-12 sec or at system chime. Check VKBDevCfg afterwards, does it lists the device in bootloading mode?

Yes, after connecting while pressing the button for ~10s and then releasing, DevCfg shows it as "VKB Boot NJoy32 platform v00.56".

When I then try to flash, bootloader finds the device and the blue light turns on while flashing, but when finished bootloader disappears (DefCfg does the same), the lights are off again and when I restart DefCfg, the device is not listed any more.

Follow this procedure for flashing that specific Black Box. Make sure the VKBDevCfg is off when running the zBootloader as Admin. When zBootloader is done flashing it's normal to automatically close.
To make sure there are no conflicts it is recommended to unplug all other VKB devices from USB during this procedure.

I did as described in the video, downloaded and CRC-checked the correct firmware and flashed with zbootloader.exe in admin mode, DevCfg off, no other devices connected. After flash, the BB lights remain off. Launching DevCfg, it shows no devices. I also tried this with the other BB's USB cable.

More things to try: reboot the bb with the button pressed, run VKBDevCfg, select the device at top (which should be the bootloader), then click Restart in Action tab.
Also, try other USB ports, preferably back of computer or powered hub.

I tried various USB ports (USB 2 and 3 versions) and disconnected other devices. When I launch DevCfg, "Restart" is greyed out. When I then select the device, I get the "It's necessary to update the firmware of the controller"-message and when I confirm, "Error read CPUID" appears. "Restart" remains greyed out and the CPUID-message reappears every time I click it away. Restarting from the bootloader brings the same error.
The lights on the BB are still always off except for that one light while flashing.

Post a screenshot please with the bb in bootloader mode in VKBDevCfg.

This is what I get when launching DevCfg right after putting BB in bootloader mode:

when clicking Ok, I get:

then I get this now:
although yesterday I immediately got the CPUID error again in an endless loop after clicking ok.

When I then click the device name, I now get
I didn't get that error yesterday.

Other computer available to try this on?

Just tried it on a laptop, same behavior. Not surprising, as it worked on my PC before and the SGC still works there and could be flashed as well.

Turn of VKBDevCfg and run zBootloader in Admin. Start the BB in bootloading mode by connecting to USB while holding the button pressed.
Take screenshot and upload it.
Select the bootloader device, then the ... button, navigate to your firmware and load it up. Click the Flash It! button.
Take screenshot and upload it.