Got this Hitachi model 31UX5BC with a rather tough problem to diagnose. The symptom was that the raster was pulled in several inches on each side - not bent at all like you'd see with a bad yoke or pincushioning problem. Just doesn't seem to be enough horizontal width. Otherwise the set is fine - great picture, sound, etc. Went to work on the thing and found Q752 (NTE 56, pincushion amplifier??) shorted, replacing this made no difference but the replacement transistor quickly overheats. I've checked every diode, cap, and resistor I can think of, all leads turn up nothing. Has anyone else seen this problem, and could they possibly provide me with some help? Thanks for any advice.
31" Hitachi TV Shrunk Raster
Jun 03, 2005
3 Replies
I would not be able to tell you exact components.
I would be looking for something that is shorted, or overloading the horizontal scan or pin amp areas. It is also possible to have a bad yoke to cause this problem. In the yoke their may be a pin winding, or some other types of components incorporated. You would have to investigate this.
Did you check for any shorting or any high ESR capacitors?
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Jerry G. =====
I had checked the caps with a fluke DMM (don't have an ESR meter) and they had checked fine. Suspecting that maybe one was breaking down under load, I tried disconnecting a .015uF cap near Q752. Bingo! Full raster. Time to invest in an ESR meter I guess. Thanks for the advice, I had suspected a retrace cap right from the start and that's what I should have stuck with.
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A quick follow-up; Q752 is still overheating, and the replacment capacitor has failed also. More leaky caps that I'm overlooking?
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