Dr Mullerr Orbit bank of bulbs out

Ok, need some help here.
Ive had two, apparently idiot, electricians try to help fix this but they failed. So Im hoping someone out there has the know how i need.

Ive got 4 or 5 bulbs out in a row in the canopy of my Original Dr Muller Orbit.
Its not the lamps, lamp holders, starters or capacitors.

Any thoughts on what is causing this?
Id appreciate any help.

Thanks!