As the initial symptoms were completely dead, it is worth going over the EP circuit board while powered on & gently tapping components with the insulated handle of a screwdriver to see if anything changes the screen display (makes it flicker or go off etc).
If it reliably gets better as it warms up you need to get yourself some component freezer spray. Then spray each component in the video circuit one at a time until it makes a difference. Maybe it will be the Nick chip but also it may be a resistor, capacitor or transistor, they are 30 years old after all.
