Put a new end on a coax. No problem, then I touch some part of it while kneeling on floor and get a small zap. Ok did not think much of it. Plug new hdmi into tv. Nice big spark and a blackened hdmi cable end. Box also had rf cable going to tv. Moved it just right and sparks were going between body of f con and nut section. I ended my service for the day there.
I assume neutral is lost somewhere. Correct.

local cable company had a house burn down when drop was disconnected at tap recently. From what I hear, again a neutral problem. When drop was disconnected some power strips took a dump and lit place up.

Pocket voltage age detector shows nothing on coax. I assume if it were disconnected you could probe with DMM and find voltage.

If it's connected, you won't see voltage unless the device it's connected to isn't connected to anything else.

Look at the point where the coax enters the building and if it's not grounded, call the local cable provider and tell them to fix their problem- don't change anything, just tell them what you saw.

Had a similar problem, a receptacle had the ground the and neutral crossed in an upstairs bedroom. the sat guy plugged in a receiver to this outlet and everything was ok. we where connecting the sat receiver in the rack and sparks happened. the power went through the coax, took out the LNB, directv switch, the receiver that was going into the rack, denon receiver HDMI, and blu-ray player HDMI.

? If it were disconnected you couldn't measure any voltage. There has to be a "ground" or reference point, and another point that is connected to something that is not at "ground" potential.