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Horrible Hitachi - Last Call for Help


Chris F.

Jan 1, 1970
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.....


Jan 1, 1970
kip said:


and stop using POS NTE semis!!!!!!!


actually, in non-critical applications, you can get away with using
these, but in high freq, fast switching, high pulse applications (like
pincussion circuits!!!), they rarely work correctly.

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