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Toshiba 27A10 TV [Followup]

This 10 y.o. TV has a fine picture and satsifies my needs. Several months ago a slightly brighter horizontal line would appear intermittently @ the bottom 5th of the screen. Not very annoying and I knew my skills would not be sufficient to fix until failure occurred. Eventually, the picture did collapse to a single bright horizontal line. I suspected the vertical drive. With no schematic, I removed the chassis [easy] and looked for a bad solder joint, bulging cap or other obvious failure. Found none but reflowed a few joints around what I guessed to be the vertical IC. TV worked fine. Joy. Failed again after a few weeks and process repeated 3 X. Frsutration. I then simply turned the TV off and on and the picture was immediately restored. TV remains fine for weeks before next episode. Since the TV is not cooling down and I am applying no physical pressure, I think I should rule out a thermal issue or bad solder joint. I'm thinking more along the lines of a marginal cap. But I have no ESR [would this even show?] or schematic. Does that sound like a good guess? Does anyone know exactly which cap [by schematic # or value] I should replace [as I'd rather not replace them all]? Thank you for any comments.

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Reply to
John Keiser
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Toshiba's and a few other brands had problems with caps. But the one that you might be looking for is not near the vertical chip. The cap that you'll need to, mostlikely, replace is going to be either a 1uf or 10uf 50v cap at the vertical output of the Video jungle chip.... You'll need to lookup the Jungle data to find the vertical output pin and follow the trace to the cap. Also, depending on the vertical chip used, you may have a flakey resistor that is in Vertical circuit cluster. The value is usually around 33k to

47k. You can always find the Vertical output chip by following the yoke connection. The 2 wires that DO NOT go to the HOT are the vertical. And the chip is a SIP mounted on an aluminum wide U shaped (as seen from above) heat sink. Get the chip data sheet to find the resistor that I mentioned above... If it's a chip resistor just knock it off and replace it with a 1/4 watt resistor. Again, depending on the chip, the data sheet may show a different value for the resistor in the test schematic... but, you'll need to go by what's in the set for it to work properly and give a full picture. So try to check the value of it with your DMM first before attempting to remove it or try to see the value of the bands or printing (if it's a chip resistor (333, 473...etc). No schematic really needed on this type of repair... as long as all the values are readable.

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Reply to
Anonymous

Next time this fails, I'll follow your detailed tips.

BTY, what is the meaning/origin of "video jungle" chip?

Thank you for taking the time to write extensively.

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Reply to
John Keiser

The Video Jungle chip is the large chip on the board that accepts the video signal from the tuner (Post I-F). Depending on the particular chip you have in your set, it's responsible for Sync Separation (Vertical and Horizontal) , RGB separation and some VJ chips (Pre I-F) output the composite audio that would then go to the audio amp or into a stereo demodulator/SAP seperator. The chip also accepts the video controls like Brightness, Contrast, Color, Hue... either via POTs (older sets) or microprocessor control. Sometimes, you can find this chip on the board by following the wire bundle from the CRT driver card that plugs into the picture tube.

If you were to see even the block diagram of this type of chip, you'd see that the term "Jungle" would fit nicely.. It's an assortment of amps, buffers, error correction, demodulation, Filters...etc..

This is an example of a Sony VJ Chip Data sheet at the following url (Plus or Minus of few pins). Toshiba may be different. You might find the data sheet for your particular chip at the site as well. I would recommend to lookup all of the chips in your set them. I didn't have any Toshiba boards to give Toshiba examples... but this should help:

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Given the description of your problem.. unless it's been fixed already, you'll definitely have the problem again be it the cap or resistor. One other recommendation... If it's the cap and it's an 85degree cap, I'd say replace it with a 105degree cap... My customers have always been happy with that choice...

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Reply to
Anonymous

In case anyone reads this thread in the future: I replaced C305 [2.2 uf] in the video circuit and all has been perfect for 1 week.

[Note: I didn't have a 2.2 uf around and used a pair of 1ufs in parallel.]

Thank you for your assistance.

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John Keiser

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