The tv sound works all the time when turned on but occasionally the video either does not come on or goes of while watching it.

It is usually a vertical deflection circuit problem. Here's the basic troubleshooting:

1. Make sure that no front panel buttons are inadvertently stuck in an "engaged" position.
2. Press MENU button. If a small horizontal line appears at the center of the screen, you have lost vertical sweep on your TV. The protection circuit shuts down the picture to protect the tubes from burning a line across them. The intermittent problem may indicate a loose solder. Try resoldering the vertical output IC. The IC along with the B+ feed resistor back in the sweep power supply is most probably bad or has a loose solder.
   
3. Press the DEVICE and MENU buttons on the front panel simultaneously and hold it for 5 seconds to activate the Error Code Operational Check. The status LED indicator will then flash denoting a two digit code.
   
4. Count the number of flashes then pauses for about a half second then flashes again. The first number of flashes indicates the first digit of the error code and the second number of flashes indicates the second digit of the code. For example, if the error code is "24", the LED will flash 2 times, pauses, then flashes 4 times. The error code is repeated a total of 5 times. Error 24 indicates a vertical deflection circuit failure.