Quote:
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.]
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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.