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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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Toshiba TV Vertical Deflection Problem, Almost Fixed…Need Ideas
I have a Toshiba 32” TV built in 1994. Model CX32D60, chassis TAC9442.
The problem started with the picture being squeezed from both the top and bottom of the screen so that only the middle one-third of the screen had any picture information. It looked like an extreme version of letterbox format. Thwacking the side of the set would cause the picture to revert to normal size. After ten minutes or so it would go back to one-third size whereupon another tap on the side of the TV would set it right again. Once the TV was warmed up, approx. ½ hour, the picture would stay normal sized. However, most of the time it would exhibit slight jittering, just enough to make the text crawl at the bottom of the screen a bit difficult to read. But sometimes the picture would lock in perfectly. Eventually this extreme letterbox became a single bright horizontal line in the middle of the screen. I would take to warming the chassis of the TV using a blow dryer aimed through the back of the TV case. Thwack, blow dryer, thwack, blow dryer, etc. This is no way to watch TV. I’ve Googled my TV’s problem and found some solutions on this newsgroup. This NG is a great resource. Thanks to all that post here. There are a couple of electrolytic capacitors in the vertical deflection circuit that lose their integrity with age (heat cycling). The two capacitors mentioned are C305: 2.2 microfarad 50v, and C342: 1 microfarad 50v. I bought replacement capacitors from DigiKey-- Panasonic brand with 105C temp rating and 63v rating. Parts including shipping was $2.35. That sure beats the TV repair shop estimate of $140.00. I avoided electrocuting myself and replaced the capacitors and also touched up the solder on the pins of the vertical IC and tested the TV. Upon initial power-up I had the familiar single horizontal line. Thwack on the side of the box. Full size picture. Crystal clear. Looking good. Then I notice there is a thin flickering horizontal line at the very top of the screen, but on only some channels. I also notice the score bar used to show information during football and baseball games and located near the top of the screen seems a bit lower than usual. It seems like the picture is not being stretched out quite enough. I’m thinking the set isn’t over-scanning the picture as much as it should. Still, it’s looking much, much better than before. The set ran for about 5 hours one night and about 4 hours the next afternoon when I once again got the dreaded single bright horizontal line. Thwack. Picture is full sized again. Crystal clear. Single, thin horizontal static-ky line at the top of the screen. TV held the full sized picture until it was shut off for the night, about another 4 hours. What other components should I suspect is causing this problem? Any ideas? |
#2
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Toshiba TV Vertical Deflection Problem, Almost Fixed…Need Ideas
"powrwrap" wrote in message ... I have a Toshiba 32” TV built in 1994. Model CX32D60, chassis TAC9442. The problem started with the picture being squeezed from both the top and bottom of the screen so that only the middle one-third of the screen had any picture information. It looked like an extreme version of letterbox format. Thwacking the side of the set would cause the picture to revert to normal size. After ten minutes or so it would go back to one-third size whereupon another tap on the side of the TV would set it right again. Once the TV was warmed up, approx. ½ hour, the picture would stay normal sized. However, most of the time it would exhibit slight jittering, just enough to make the text crawl at the bottom of the screen a bit difficult to read. But sometimes the picture would lock in perfectly. Eventually this extreme letterbox became a single bright horizontal line in the middle of the screen. I would take to warming the chassis of the TV using a blow dryer aimed through the back of the TV case. Thwack, blow dryer, thwack, blow dryer, etc. This is no way to watch TV. I’ve Googled my TV’s problem and found some solutions on this newsgroup. This NG is a great resource. Thanks to all that post here. There are a couple of electrolytic capacitors in the vertical deflection circuit that lose their integrity with age (heat cycling). The two capacitors mentioned are C305: 2.2 microfarad 50v, and C342: 1 microfarad 50v. I bought replacement capacitors from DigiKey-- Panasonic brand with 105C temp rating and 63v rating. Parts including shipping was $2.35. That sure beats the TV repair shop estimate of $140.00. I avoided electrocuting myself and replaced the capacitors and also touched up the solder on the pins of the vertical IC and tested the TV. Upon initial power-up I had the familiar single horizontal line. Thwack on the side of the box. Full size picture. Crystal clear. Looking good. Then I notice there is a thin flickering horizontal line at the very top of the screen, but on only some channels. I also notice the score bar used to show information during football and baseball games and located near the top of the screen seems a bit lower than usual. It seems like the picture is not being stretched out quite enough. I’m thinking the set isn’t over-scanning the picture as much as it should. Still, it’s looking much, much better than before. The set ran for about 5 hours one night and about 4 hours the next afternoon when I once again got the dreaded single bright horizontal line. Thwack. Picture is full sized again. Crystal clear. Single, thin horizontal static-ky line at the top of the screen. TV held the full sized picture until it was shut off for the night, about another 4 hours. What other components should I suspect is causing this problem? Any ideas? There is obviously a loose connection on a component in the vertical section, or leading to the vertical circuit. With the TV turned on and the back cover off, you need to gently poke around on the board with a non-metallic tool until you touch a component that causes the problem to go away. Or... with the TV off you should look at the solder joints with a high power magnifier until you find the suspect solder joints, and resolder those spots. If you keep heating and cooling the TV or whacking it on the side, eventually some of the components will fail completely. If the failure causes a bright enough horizontal line, it can burn into the CRT making a permanent line. You are on the right track but you must fix it right before more damage is done that you can not repair easily. |
#3
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Toshiba TV Vertical Deflection Problem, Almost Fixed…Need Ideas
On Oct 20, 7:25*pm, "Mike S" nospam wrote:
There is obviously a loose connection on a component in the vertical section, or leading to the vertical circuit. With the TV turned on and the back cover off, you need to gently poke around on the board with a non-metallic tool until you touch a component that causes the problem to go away. Or... *with the TV off you should look at the solder joints with a high power magnifier until you find the suspect solder joints, and resolder those spots. If you keep heating and cooling the TV or whacking it on the side, eventually some of the components will fail completely. *If the failure causes a bright enough horizontal line, it can burn into the CRT making a permanent line. *You are on the right track but you must fix it right before more damage is done that you can not repair easily. Since the capacitors were replaced the bright horizontal line has occurred twice--upon initial turn-on after replacing caps and once after about 8 hours of operation. So I've only had to whack the TV two times since replacing the caps. And I've not used the blow dryer at all since the repair. I did look at the solder joints in the vertical section with bright lighting and didn't see anything amiss. Nevertheless, as long as I had the TV opened up I did touch up the vertical IC pins. I suppose it if happens again I could remove the back of the case and try poking various components (instead of whacking the TV) to make the bright horizontal line disappear and isolate the offending component. For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen? |
#4
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Toshiba TV Vertical Deflection Problem, Almost Fixed.Need Ideas
For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen? ********************* I'm only guessing at this, but I think what you're seeing is not static but digital data. I see the same thing at the top of my TV picture (an HDTV signal converted to be visible on a regular analog TV). Normally this isn't seen because it's supposed to be above the viewing area of the picture itself. Closed-captioning and other information is embedded in the "vertical blanking interval," or the brief instant between frames of video. |
#5
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Toshiba TV Vertical Deflection Problem, Almost Fixed…Need Ideas
On Mon, 20 Oct 2008 19:20:59 -0700 (PDT), powrwrap
put finger to keyboard and composed: I did look at the solder joints in the vertical section with bright lighting and didn't see anything amiss. Nevertheless, as long as I had the TV opened up I did touch up the vertical IC pins. I suppose it if happens again I could remove the back of the case and try poking various components (instead of whacking the TV) to make the bright horizontal line disappear and isolate the offending component. There should be a low ohm resistor in the vertical yoke circuit. I believe this resistor provides current feedback to the vertical output IC. Check it for bad solder joints. For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen? As someone alse mentioned, this is probably digital information transmitted during the vertical retrace period. Here in Australia it could be teletext. IME those lines are invariably caused by dry capacitors in the vertical section. Just change all the caps in the vicinity. As still another person mentioned, some Toshiba chassis also have a problem with a low value electrolytic near the jungle IC. This is a major multifunction IC, with 40 to 60 pins or so, which handles colour decoding, luminance, and horizontal and vertical sync outputs. It could have a TA prefix if it's a Toshiba part. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#6
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Toshiba TV Vertical Deflection Problem, Almost Fixed.Need Ideas
"Matt J. McCullar" writes:
For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen? ********************* I'm only guessing at this, but I think what you're seeing is not static but digital data. I see the same thing at the top of my TV picture (an HDTV signal converted to be visible on a regular analog TV). Normally this isn't seen because it's supposed to be above the viewing area of the picture itself. Closed-captioning and other information is embedded in the "vertical blanking interval," or the brief instant between frames of video. That's what it sounds like. He should check for a bad capacitor in the vertical output as well. -- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#7
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Toshiba TV Vertical Deflection Problem, Almost Fixed.Need Ideas
On Oct 20, 11:06*pm, "Matt J. McCullar" wrote:
I'm only guessing at this, but I think what you're seeing is not static but digital data. *I see the same thing at the top of my TV picture (an HDTV signal converted to be visible on a regular analog TV). *Normally this isn't seen because it's supposed to be above the viewing area of the picture itself. *Closed-captioning and other information is embedded in the "vertical blanking interval," or the brief instant between frames of video. Excellent theory, and I agree. This problem is most noticable on the local PBS station that broadcasts in HD. Also those channels that have the 16:9 digital signal seem to show this problem the most. Local analog stations don't have it. Thanks to everyone for the suggestions. I'll look for the cap near the "jungle IC"--though it's usually not mentioned when discussing my model number TV-- and check out the low ohm resistor. |
#8
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Toshiba TV Vertical Deflection Problem, Almost Fixed.Need Ideas
"Samuel M. Goldwasser" wrote in message ... "Matt J. McCullar" writes: For now, I'd like to solve the thin horizontal line of static that happens at the very top of the screen. This seems to me to be a component that is on the hairy edge of failing--I don't think that poking it will cause the problem to go away--but I'm not certain. Anybody have any other ideas on why there is a line of static at the very top edge of the screen? What you are seeing is line 21 which contains the closed caption data. Most sets overscan a bit and this should be off of the screen. David |
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