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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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Toshiba vertical problem
Repaired a Toshiba t.v. with a vertical problem caused by bad
capacitors. After fix, vertical is short on top and bottom equally. Attributing this to set needing adjustment upon new components. Size can be properly adjusted with vert height adjust. Problem now is that vertical size flucuates a bit depending upon brightness of scene being displayed. It isn't very noticeable, but I am wondering if it is normal operation or if there is some other problem. Maybe it's just the way it's designed because I see no regulation of the vert out supply. Seems like if there is a problem it would be with voltage regulation, but vert out supplies seem reasonably stable (a bit of variation, maybe .2 V). It's not vert supply filter capacitors, ripple remains constant. I don't have a schematic, but the supply to vert out comes from flyback so if vert supply is varying, then B+ must be varying too much? Customer saw the set and didn't notice the problem, am I just being too critical? |
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Toshiba vertical problem
David Wolff:
With a variac do a basic main power supply B+ regulation check to verify that it holds regulation when the AC Line input is varied from about 105 to 120 V. You also may want to check and/or replace the filtering electrolytics in the main B+ supply...... and also check the flyback derived B+ electrolytics. Also you could be seeing the result of screen supply regulation problems, particularly if the picture size changes when the average brightness level changes..... around the flyback look for low uf / high voltage electrolytics...... i.e. 10uf @250 v .... or similar. -- Best Regards, Daniel Sofie Electronics Supply & Repair - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "David Wolff" wrote in message om... Repaired a Toshiba t.v. with a vertical problem caused by bad capacitors. After fix, vertical is short on top and bottom equally. Attributing this to set needing adjustment upon new components. Size can be properly adjusted with vert height adjust. Problem now is that vertical size flucuates a bit depending upon brightness of scene being displayed. It isn't very noticeable, but I am wondering if it is normal operation or if there is some other problem. Maybe it's just the way it's designed because I see no regulation of the vert out supply. Seems like if there is a problem it would be with voltage regulation, but vert out supplies seem reasonably stable (a bit of variation, maybe .2 V). It's not vert supply filter capacitors, ripple remains constant. I don't have a schematic, but the supply to vert out comes from flyback so if vert supply is varying, then B+ must be varying too much? Customer saw the set and didn't notice the problem, am I just being too critical? |
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