If you were to pick it up and move it around in your hand (props off of course), does it lose signal due to shaking, certain orientations or not at all? If not at all, then I'd assume brown-outs to be the issue. if it is shaking, I'd guess a short or loose connection. If it is certain orientations, then it could be an antenna issue.
Good steps to diagnose, would just add that static usually means connection between cam and VTX is fine, something between (or including) VTX and video receiver since it's losing the signal entirely. If the VTX and receiver are working but cam is disconnected or not working you usually just get a black screen instead of static.