I was setting up a mobile power supply for my Raspberry Pi 2 consisting of: - a 12V Battery - a step down power converter that converts 7-24V to 5V/3A
It was working fine until I connected the battery to my power supply for charging while the system was running. That shouldn't be a problem but I was so dumb to first connect +battery with +supply while the power supply was switched off. As expected, the RPi was rebooting due to power loss but since then HDMI output does not work. Everything else seems to work just fine.
I did that failure again to measure what happens. I figured out all that happens is that VUSB was grounded very shortly and must have been back to 5V after approx. 500us.
Is there some special component as part of the HDMI circuit that might be broken and can be replaced? What could it be?