1968 Motorola works in a drawer

[old_tv_nut]

As stated above, this is due to the video output transistor in that color saturating, that is, driven to the point where the collector-emitter voltage goes to zero or minimum possible. There may be a video drive limiting adjustment somewhere or a bias or G2 adjustment that will improve it. It can occur if the particular CRT (due to either original tolerances or age) requires cutoff voltages that then make the video outputs be run at low collector voltages. Referring to service info that shows the scope traces at the cathodes can tell if the outputs are biased lower than usual even though the video B+ is normal.

[Edit: oops - I just saw your post about G1 being low. This will definitely cause this problem, because the cathodes now must be lower also so that the CRT is not cut off.]

[maxhifi]

Originally Posted by old_tv_nut

[Edit: oops - I just saw your post about G1 being low. This will definitely cause this problem, because the cathodes now must be lower also so that the CRT is not cut off.]

Probably I should have checked this up front, chalk it up to a lack of experience. It also makes sense logically to me because the brightness control has to be in the top 1/3 of its range to produce a picture at all. I guess the low bias on G1 is requiring the video outputs to be driven into clipping to get a picture, and the effect is more noticeable with saturated colors. Will be interesting to see what happens when G1 is at the correct 94 volts instead of stuck at 0. Also not sure why the resistor went open (if it indeed is open and not a shorted G1 or shorted 10k resistor)

As an aside I find it interesting the video amplifiers are just wide open transistor stages with no negative feedback to control gain or improve linearity. This really is an early model solid state design.