Looking for Bright(ness) Ideas

[bgadow]

As I go through the pile of tv's I brought home the other day I come next to a GE C2 chassis, an 18" hybrid built in the fall of '71. (hey, so was I!) Just think, they could have bought a 4-tube Zenith but instead they bought this. Well, its not too bad.

It powered up without drama, it has color. First problem to tackle-I cannot turn down the brightness. I can turn the contrast, brightness, brightness limit, all the screen & drive controls down, and still the picture is at 'normal' brightness. The little troubleshooting chart in the Sams said to check Q305, the blanking transistor. This seemed plausible since I can see blanking lines clearly unless I ramp the brightness all the way up. Voltages there seemed okay but I went ahead & swapped it out; no change. I've swapped the video output tube, the voltages around there seem within reason, too. I don't understand the circuit well enough to know where to go next.