You guys must be sick of hearing from me with this 31UXB5 Hitachi, but I promise this will be the last post. The original problem was that the raster was far too narrow at the sides, the pincushion amp transistor was shorted as were a couple of other components in that area. Replacing the components appeared to get the set working, though I was only seeing the picture from an angle since the set was turned around on the bench (more on that in a minute). BUT - the replacement transistor (NTE 56) was running far too hot. I spent ages on this set, checking every last component in the horizontal osc, output, and pincushion stages. Even did a ring test on the flyback and yoke, no problems showed up. In desperation, I tried replacing the pin amp xistor with a much larger one (NTE 2324 !), on a bigger heatsink. Needless to say it ran within its specified ratings, so I finally turned the set around and looked at the full picture - and was only half surprised to see the pincushioning totally out of whack. Classic bowtie-shaped picture. It appears that the pincushion circuit is having no effect at all; the pincusion and horiz. width controls don't do anything. Something seems to be shorting out the pincushion signal, but what??? At this point I can only offer one more guess - high ESR caps. The caps all tested great on a regular cap checker, but I do not have an ESR meter to check them with. I'm actually planning to take the caps to a friend who has such a meter in his shop, and get him to test them for me. Suppose they'll test bad? Any help would me much appreciated. At this point the set is very close to being returned to the curb from whence it came.....
- posted
18 years ago