TV problem, image flickers up and down

[TheManuel]

This is only arcade related in a roundabout way but with so many people here well versed in CRT screens, I figured I should ask.

I bought a JVC TV (the one with component video in that a lot of people have) in 2002 for use with an arcade machine but did not really use it for that purpose until this year. 

In the meantime, I had another TV (Panasonic) in the basement which I had mounted high on a wall bracket and tilted downwards at about 15 degrees.  Since I'll be using the JVC for the arcade machine, I had to use the Panasonic for my family room.  The Panny TV never gave me any problems before.  However, as soon as I placed it on my family room's entertainment center with no tilt, the image will often start "jumping" up and down fast.  I don't know how to describe it.  It's not a scrolling effect but rather a stuttering, if you will.  If I give it a bump with my fist at the top, it will start working well but eventually the problem returns.  Also, if I hold it tilted at the same angle as it was mounted in the basement, it will work fine too.  It is as though the TV has "grown accustomed" to being tilted.
The first few days after I moved the TV to the family room the problem was much worse and over the course of a few days, it became less frequent although to frequent still for comfort.  I was hoping that over time it would go away but it's been months now and the problem happens every day.

Does anyone know if there is anything I can try to fix it myself without taking it to a TV shop (I'm broke)?

PS: While on this subject, the JVC TV has had the tuner damaged for years.  Channels from 2 to 6 or 7are almost always showing white noise, from 7 or 8 to about 47, it's hit and miss and from 48 onward they are always fine.  Is the tuner a single component I can buy and replace with some soldering?

I'll appreciate any advice.

Thanks a lot.

[grantspain]

you probably have a dry solder joint on the monitor chassis causing the jumping-could be on one of the input connector or one of the components

[TheManuel]

Thanks for your answer.

So, conceivably, I could just lay a droplet of solder on the culprit joint?
I bet the devil is in finding which one 

[grantspain]

well you need to practice soldering really,solder has to be applied rather than blobbed on the joint
finding the suspect joint could be a problem if you have no experience

dry solder joints are normally very noticeable as there will be a crack around the joint

[TheManuel]

Very well.
I will look around carefully.
I'm not terrible at soldering so I can probably do a decent job of fixing the joint/s I find them.

Thanks.