RCA 21-D-7177 Horz Drive Issues

[Kevin Kuehn]

Originally Posted by Penthode

Hi Kevin,
I suppose I am now a little confused. I recall the original problem was that the center of the horizontal scan is to the right. This means that the left side is stretched and at the same time the right side is compressed. Is that correct?

Correct. Horizontal center was originally off to the right using the sets 21AMP4 CRT. When I changed to the 8XP4 test CRT, then I discovered the opposite true. Also, with the 8XP4, I'm not able to see the left edge of the horizontal scan. I suppose I should forget using the 8XP4 for these centering tests and just go with the 21AMP4?

Originally Posted by Penthode

By the width control being all the way out, does this mean the core of the width coil is out so you have minimum width? Then I suppose overall you have the necessary width adustment range but the left side is still stretched.

Correct, but really only became an issue when I switched to the 8XP4 test CRT. And this extreme reduction in width was only in an attempt to see the left scanning edge.

Originally Posted by Penthode

This would suggest to me you have too much horizontal drive, even with the trimmer capacitor tighted right down. Is this correct?

The Horizontal drive control is part of a capacitive divider. Perhaps there is something wrong with the trimmer? You should be able to adjust the trimmer so that as it is tightened, the left side of the raster slightly compresses and the CRT will dim slightly as the HV drops.

Maybe you should test the trimmer? Or as a test to reduce drive more, you could put a small capacitor (50 to 80 uufd) in parallel with the horizontal drive trimmer?

Terry

I'll check into reducing the horizontal drive even more and report back. I've never seen any noticeable compression on the left side, even with the trimmer completely closed. I'm pretty sure I've never seen the CRT dim with it fully closed. I know the trimmer checks ok, but I've yet to check the value of C105 (mica 560 pf). Using the sets 21AMP4 CRT, I generally get the best horiz linearity with the trimmer fully closed. This would seem to indicate there is still too much horiz drive.