[old_tv_nut]

I'm looking at the SAMS 25MC30 schematic from the earlytelevision site, and it appears vertical blanking is a 90 v pulse from the vertical output plate (V10 6HE5 pin 6) coupled through C34 (.015 1kv 10%) and R66 (150k) to the video outut circuit. You might check these components, but it seems a little strange to me that you have the same problem on both sets if their circuits are alike.

The G2 setup procedure, once you have gone through it, should end up with approximately the DC voltages shown on the CRT grids and cathodes. In the setup position, the cathodes are at a fixed standard voltage, and G2's are adjusted to just barely be above cutoff with no color signal and nominal voltages on the grids. If proper cutoff cannot be reached with the G2 controls (due to CRT variation [edit - or demodulator tube variation]), then the grid voltages are adjusted slightly with the CRT bias control so that the cutoff point is within range of the G2's. If you do the setup out of order by accident, you may get the wrong voltages on the CRT. I think this could conceivably affect the blanking action.