Width & Focus in DuMont RA-103

[Phil Nelson]

These issues aren't necessarily related, but why not ask two questions for the price of one?

I have replaced all of the electrolytic and paper caps in my DuMont RA-103. Nice bright, stable picture, great audio. Two minor issues remain.

1. I can't reduce the width using the horizontal size adjuster. It seems to do nothing, in fact. (Horizontal hold and position do work.) If it overscans this much on the bench, I'll lose even more (1/2 inch on both sides) when it's in the cabinet behind the mask. I haven't fiddled with linearity because it looked correct when I put on a crosshatch pattern.

2. Focus ain't quite there. See photo. The focus control has an effect, but the picture should be sharper. When I'm adjusting, it reaches a point of maximum sharpness, then gets more blurry again.

Voltages look generally good, although I haven't checked everything. I have 329v on the 300v line leading to a leg of the focus control.

If I could fix only one problem, it would be the focus. It bugs me when an adjuster (width) doesn't work at all, tho'. Here is the schematic.

http://antiqueradio.org/art/temp/DuM...Schematic1.jpg
http://antiqueradio.org/art/temp/DuM...Schematic2.jpg

Thanks for any ideas.

Phil Nelson