double check you have all the plugs connected,specially the earth lead to the neck card from the tube braid-mind you you should still get some kind of picture
the only time i have had a monitor power up with heaters but not produce any kind of picture was on a tatung chassis and that was down to the video decoder ic on the neck but i am not familiar with your chassis so to say its the same fault would be a wild guess
you say the chassis has been repaired and checked,is this by a professional repair company?the reason i ask is that if the chassis did check out ok with them then maybe you should look towards things like a bent pin on the neck-something that is unique to your setup