See if you can find the datasheet on the video amp IC on the CRT neck
board, Then check the voltage on the Contrast pin. Most are in the
range of 3.5 to 4.0 volts. If yours is way less and you cannot increase
it by using the Contrast control, I suggest you experiment by manually
increasing the contrast voltage.

What I do is to locate a source of 5 or 12 volts on the board, connect
a variable resistor box between the voltage supply and the contrast
pin, then gradually decrease the resistance (increasing the contrast
voltage) until you get a good picture. Monitor the contrast voltage as
you do this. Most IC's peak out at about 4 volts.
Once you have a good picture, solder in a small fixed resistor in
place of the variable one.
Hope this helps....
John