RCA 21-D-7177 Horz Drive Issues

[Penthode]

These are my few thoughts.... I do not think there is a horizontal drive problem. Horizontal overdrive leads to non linear scanning where the beam slows during forward horizontal trace before the Horizontal output tube conducts. Instead I believe the line is displayed during the horizontal retrace.

When you adjust the horizontal hold, does the line move? If so, the problem is too slow a horizontal retrace. What you are seeing is the first vertical line in the cross hatch which should be on the left of te picture but is being displayed in the middle of the screen as the beam too slowly swings back to the left.

There are a few reasons why this may be so.

1) Is the test generator horizonal blanking wide enough. Examine the horizontal sync pulse with the scope. Horizintal blanking is supposed to be 10.9us. If the video starts too soon on the generator, you will see the white line. See the link below I found on the web:

http://www.maxim-ic.com/app-notes/index.mvp/id/734

2) The horizontal retrace is too slow due to a circuit fault. The horizontal output circuit is tuned to about 70kHz to facilitate the fast timed beam swing back t the left. Anything which may affect the horizontal "tuning" eg bad capacitor on the linearity coil, bad damper tube, shorted horizontal output transformer, shorted yoke etc may slow down the retrace.

Do you see the line on normal pictures? If not, I'd have a closer look at the cross hatch generator.