What causes the TV to go black and then when I touch the back it comes back on

This link might help: https://www.google.com/search?bih=625&biw=1366&hl=en&ei=vyUhYPnICIHUrtoPkcWQwAk&q=hOW+TO+FIX+vizio+V505-G9+led+tv.+Power+light+comes+on+but+has+black+screen&oq=hOW+TO+FIX+vizio+V505-G9+led+tv.+Power+light+comes+on+but+has+black+screen&gs_lcp=CgZwc3ktYWIQAzoFCAAQkQI6CAgAELEDEIMBOggILhCxAxCDAToCCAA6AgguOggILhDHARCjAjoFCC4QsQM6BAgAEEM6BQgAELEDUNmTBVjSrgVgvLoFaABwAHgBgAHmAYgB4wqSAQU4LjMuMZgBAaABAaABAqoBB2d3cy13aXrAAQE&sclient=psy-ab&ved=0ahUKEwi5pN_RnNruAhUBqksFHZEiBJgQ4dUDCA0&uact=5

It was the power board,but it is definitely the power board now don't touch anything while it's plugged in .

is there anything buy that has a magnet in it it demanatising screen move it away from screen or put on shelf were it not touching tv.

Buddy the main cause of this types of problem can be shot circuit. if it is so then you have to go for service.

If your tv is working but power button doesn't work then you can unscrew it and have a look. see whether button touch the sensor(it is in black color). it doesn't touch then you have to make it enable to touch by add some layer of paper or plastic,,(tips. don't ever use metal object). ; )

It sounds like the High voltage transformer has gone out. If you open the back of the tv and look on the right side, you will see a large (4 - 5 inch) black cylinder with a large wire coming out of the top. without touching anything, look and see if it is cracked.

check your power board, most likely that's the part that is causing the problem.

This is a coil, now a NOISY coil.. It is a common problem, and happens often. The whine is caused by current passing thru the copper windings and making them vibrate! A commonly accepted repair for this situation is to squirt some regular old super glue into the copper windings and let it harden for a few minutes..Viola! no more whine!

had the same problem if you have any skills with soldering open it up and check on the pins on the thing in the back lefthand corner. On mine the solder has a circular crack around one of the pins that when the back was on on it pushed the chip itself up and cause that one pin to not touch. The thing i refer to is the black tower that has 2 philip type "screw" that you turn to change the defalt color or somthing like it. well hope what i said help if you have not trashed it or got a new tv... or both.

you have either a bad flyback, bad HV splitter or a Bad HV lead. Can you remove the rear panel and try to see where the hissing is coming from without touching anything? Then let me know, as those type of repairs are easy but you cant touch any parts while trying to determine where the sound is coming from

http://cmpalmer.blogspot.com/2006/11/fixing-my-own-tv-part-ii.html