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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Tip for Toshiba TV verical repair
I inherited a Toshiba model CF2750K, chassis# TAC 9011, with the notorious vertical problem...compressed to center and upper half...bottom half dark. After reading some of the posted hints, I arbitrarily replaced the 1uf-50v capcitor in the verical section. It seemed to be the only 1uf in the vertical section, but it was C-305 rather than the C-301 or C-342 mentioned by others. One mentioned that the quality of the capacitor was important, so I replaced it with a paper-tubular (mylar?) 1uf-200v. But apparently, the set may have had two defects, because when I turned it on, it now had no vertical deflection at all (bright horizontal white line in middle). I believe the handling of the PC-board had caused a lingering problem to appear. I arbitarily re-soldered the seven in-line pins on IC-301 which I believe is probably the Vertical power IC. It had a large heat-sink. The set now worked about normally, except that the vertical linearity was a little disappointing...a slight widening of spacing progressing from bottom toward top, with and exaggerated widening on the top inch of the screen. I could only find one pot named vertical height, but could find nothing for vertical linearity. There were other un-named pots in another section but did not to turn them, and they were sealed. They did not have the expected 300 series number. I did shunt an extra 660uf across an existing 2200uf (300 series) and shunted an extra 25uf across an existing 10uf (300 series)...both in the vertical section. Adding these made no significant improvement. Incidentally, capacitors of about 3/8" diameter can be tack-soldered on the bottom side (just enough space) without removing the original (electrolytics almost never short). Does anyone have any hints as to improving the vertical linearity on this model?Is it possible that the high quality of my 1uf capacitor was TOO high? (one poster suggested that the circuit was very critical to the quality of the 1uf capacitor) |
#2
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Tip for Toshiba TV verical repair
Sorry, you mentioned that electrolytics almost never short?
That wouldn't be correct. They certainly do fail, usually in the shorted condition. You may have other caps that are leaking, try using a hair dryer and heat near the other caps and see if any of the picture has altered. If it gets better, you know you have a bad cap. If you freeze it (using cold spray), you may find the faulty cap short out completely and may blow the vertical drive IC. Typically, the vertical drive IC generates a lot of heat, most of the caps around it fail because of the heat. If you removed a 1uF electrolytic, most likely it was polarized. Did you purchase a mylar cap that was polarized?? A tantalum cap would be of the best quality, and values typically don't exceed 1uF. Tantalums are typically polarized. I would also change the vert drive IC, I don't know if you mentioned you did (couldn't tell from your post). It is possible this is the route cause of the trouble, causing other components to fail in a cascading effect. "Gene Gardner" wrote in message ... I inherited a Toshiba model CF2750K, chassis# TAC 9011, with the notorious vertical problem...compressed to center and upper half...bottom half dark. After reading some of the posted hints, I arbitrarily replaced the 1uf-50v capcitor in the verical section. It seemed to be the only 1uf in the vertical section, but it was C-305 rather than the C-301 or C-342 mentioned by others. One mentioned that the quality of the capacitor was important, so I replaced it with a paper-tubular (mylar?) 1uf-200v. But apparently, the set may have had two defects, because when I turned it on, it now had no vertical deflection at all (bright horizontal white line in middle). I believe the handling of the PC-board had caused a lingering problem to appear. I arbitarily re-soldered the seven in-line pins on IC-301 which I believe is probably the Vertical power IC. It had a large heat-sink. The set now worked about normally, except that the vertical linearity was a little disappointing...a slight widening of spacing progressing from bottom toward top, with and exaggerated widening on the top inch of the screen. I could only find one pot named vertical height, but could find nothing for vertical linearity. There were other un-named pots in another section but did not to turn them, and they were sealed. They did not have the expected 300 series number. I did shunt an extra 660uf across an existing 2200uf (300 series) and shunted an extra 25uf across an existing 10uf (300 series)...both in the vertical section. Adding these made no significant improvement. Incidentally, capacitors of about 3/8" diameter can be tack-soldered on the bottom side (just enough space) without removing the original (electrolytics almost never short). Does anyone have any hints as to improving the vertical linearity on this model?Is it possible that the high quality of my 1uf capacitor was TOO high? (one poster suggested that the circuit was very critical to the quality of the 1uf capacitor) Sorry, you mentioned that electrolytics almost never short? That wouldn't be correct. They certainly do fail, usually in the shorted condition. You may have other caps that are leaking, try using a hair dryer and heat near the other caps and see if any of the picture has altered. If it gets better, you know you have a bad cap. If you freeze it (using cold spray), you may find the faulty cap short out completely and may blow the vertical drive IC. Typically, the vertical drive IC generates a lot of heat, most of the caps around it fail because of the heat. If you removed a 1uF electrolytic, most likely it was polarized. Did you purchase a mylar cap that was polarized?? A tantalum cap would be of the best quality, and values typically don't exceed 1uF. Tantalums are typically polarized. I would also change the vert drive IC, I don't know if you mentioned you did (couldn't tell from your post). It is possible this is the route cause of the trouble, causing other components to fail in a cascading effect. |
#3
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Tip for Toshiba TV verical repair
Gene:
Replace (remove the old caps, don't shunt them) the remainder of the C3xx caps in and around the vertical output chip and look especially for C301, it is hiding about 2 inches away from the rest of the C3xx caps and is toward the center of the board near a large chip (jungle IC)..... and definitely replace it.... usually 1uf @ 50V ..... Most of the electrolytic caps, with age and heat will suffer from high ESR, degraded capacity, leak corrosive electrolyte and many times will become electrically leaky or even short...... because of this you need to actually remove the caps, don't shunt them. Unless you have an ESR meter to properly test them, just replace them all, there are only about 6 to 8 units so it is fairly easy and cheap. When replacing the electrolytics be certain to observe polarity. -- Best Regards, Daniel Sofie Electronics Supply & Repair - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "Gene Gardner" wrote in message ... I inherited a Toshiba model CF2750K, chassis# TAC 9011, with the notorious vertical problem...compressed to center and upper half...bottom half dark. After reading some of the posted hints, I arbitrarily replaced the 1uf-50v capcitor in the verical section. It seemed to be the only 1uf in the vertical section, but it was C-305 rather than the C-301 or C-342 mentioned by others. One mentioned that the quality of the capacitor was important, so I replaced it with a paper-tubular (mylar?) 1uf-200v. But apparently, the set may have had two defects, because when I turned it on, it now had no vertical deflection at all (bright horizontal white line in middle). I believe the handling of the PC-board had caused a lingering problem to appear. I arbitarily re-soldered the seven in-line pins on IC-301 which I believe is probably the Vertical power IC. It had a large heat-sink. The set now worked about normally, except that the vertical linearity was a little disappointing...a slight widening of spacing progressing from bottom toward top, with and exaggerated widening on the top inch of the screen. I could only find one pot named vertical height, but could find nothing for vertical linearity. There were other un-named pots in another section but did not to turn them, and they were sealed. They did not have the expected 300 series number. I did shunt an extra 660uf across an existing 2200uf (300 series) and shunted an extra 25uf across an existing 10uf (300 series)...both in the vertical section. Adding these made no significant improvement. Incidentally, capacitors of about 3/8" diameter can be tack-soldered on the bottom side (just enough space) without removing the original (electrolytics almost never short). Does anyone have any hints as to improving the vertical linearity on this model?Is it possible that the high quality of my 1uf capacitor was TOO high? (one poster suggested that the circuit was very critical to the quality of the 1uf capacitor) |
#4
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Tip for Toshiba TV verical repair
Ditto Sofie's comments. Also, clean any electrolyte from the board and
resolder all connections in the circuit. The 200v cap may have a high ESR and may also cause problems. Use the original value electrolytics. Leonard "Sofie" wrote in message ... Gene: Replace (remove the old caps, don't shunt them) the remainder of the C3xx caps in and around the vertical output chip and look especially for C301, it is hiding about 2 inches away from the rest of the C3xx caps and is toward the center of the board near a large chip (jungle IC)..... and definitely replace it.... usually 1uf @ 50V ..... Most of the electrolytic caps, with age and heat will suffer from high ESR, degraded capacity, leak corrosive electrolyte and many times will become electrically leaky or even short...... because of this you need to actually remove the caps, don't shunt them. Unless you have an ESR meter to properly test them, just replace them all, there are only about 6 to 8 units so it is fairly easy and cheap. When replacing the electrolytics be certain to observe polarity. -- Best Regards, Daniel Sofie Electronics Supply & Repair - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "Gene Gardner" wrote in message ... I inherited a Toshiba model CF2750K, chassis# TAC 9011, with the notorious vertical problem...compressed to center and upper half...bottom half dark. After reading some of the posted hints, I arbitrarily replaced the 1uf-50v capcitor in the verical section. It seemed to be the only 1uf in the vertical section, but it was C-305 rather than the C-301 or C-342 mentioned by others. One mentioned that the quality of the capacitor was important, so I replaced it with a paper-tubular (mylar?) 1uf-200v. But apparently, the set may have had two defects, because when I turned it on, it now had no vertical deflection at all (bright horizontal white line in middle). I believe the handling of the PC-board had caused a lingering problem to appear. I arbitarily re-soldered the seven in-line pins on IC-301 which I believe is probably the Vertical power IC. It had a large heat-sink. The set now worked about normally, except that the vertical linearity was a little disappointing...a slight widening of spacing progressing from bottom toward top, with and exaggerated widening on the top inch of the screen. I could only find one pot named vertical height, but could find nothing for vertical linearity. There were other un-named pots in another section but did not to turn them, and they were sealed. They did not have the expected 300 series number. I did shunt an extra 660uf across an existing 2200uf (300 series) and shunted an extra 25uf across an existing 10uf (300 series)...both in the vertical section. Adding these made no significant improvement. Incidentally, capacitors of about 3/8" diameter can be tack-soldered on the bottom side (just enough space) without removing the original (electrolytics almost never short). Does anyone have any hints as to improving the vertical linearity on this model?Is it possible that the high quality of my 1uf capacitor was TOO high? (one poster suggested that the circuit was very critical to the quality of the 1uf capacitor) |
#5
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Tip for Toshiba TV verical repair
Like mentioned earlier, look for another 1uf. There are 2 identical 1uf or
2.2uf caps used (depending on model), one is near the vertical output IC, the other is close to the larger osc/video jungle IC. Look at the color and size/shape of the original and compare with other C300 series in the set until you find it's matching cap. Funny thing is these caps normally check OK on both an ESR meter as well as a cap checker, but cause linierity problems. You need to replace them both. Ron |
#7
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Tip for Toshiba TV verical repair
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#8
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Tip for Toshiba TV verical repair
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