the only thing i did not test is the 5V step up regulator, of course. This Vreg was working but sitting in a bag for > 1yr.
so I connect the lipo again to test, and there goes the smoke from the 5V step up regulator. then I changed another same kind 5V regulator. the vTx still getting hot, as it should and checked the voltage into the vCam and vTx, both at 4.98V perfect.
The only thing is there is no video any more. Checked the voltage acroos video out from vCam to gnd is 0.02V.

Another thing is, there is no video signal at all, blank not even noises on the screen.
Can a shorted Vreg sends current to burn out the vCam? There is no sign of any burns on the vCam circuit/chips.