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 TV Repair Casebook. No.1
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 Return to top of page · Post #: 1 · Written at 5:37:04 PM on 18 September 2019.
Labrat's avatar
 Location: Penrith, NSW
 Member since 7 April 2012
 Member #: 1128
 Postcount: 316

Hi All.
Just an idea. A sort of “The Serviceman Who Tells” section where you can discuss repairs you have undertaken, which might be of interest to members of the forum.

Nowadays the main theme of my collection is Vintage TV, and Video Tape Recorders.
Since there is not a lot happening on the forum at the moment, I've decided to begin relating some of the faulty sets I've repaired. Their symptoms, and ultimately what was wrong with them.

I shall put up a few posts, and if there is interests, will continue to post like articles.

So let's begin. Most recent repair, a Toshiba Colour television model C-1821.
An eighteen inch brown plastic portable ? Well it does have a handle and twin telescopic aerials.
Should have come with a Lifting hook and health insurance.

Anyway, the complaint was that the picture would roll (vertically). The vertical hold control would have limited success in locking the picture. Once delivered, the fault appeared to be weak vertical sync. The picture could be made to roll in either direction, and the control looked to be centred. Whenever the set was cold, the picture did not even try to lock as the picture's blanking bar came to the top of the screen. After a few minutes, the picture could be locked, but not as strongly as I thought it should.

Without an exact circuit, I found something that looked close. A circuit that had the same vertical/horizontal processor i.c. With waveforms and voltages. First, because I am lazy, I checked the electrolytic caps, which were surprisingly all good.
Discouraged, next I called on the assistance of a big black bird, a C.R.O.

The sync pulses were present, but larger than specified. I checked the associated components to no avail, then sprayed some freeze onto the chip. Vertical lock was again lost until the chip warmed again. There was no change in the amplitude of the sync pulses. Fitting a new TA7609P chip and socket returned the set to a very strong vertical lock, and the correct level of sync.

My theory, a low gain transistor somewhere inside the chip, as the sync input pulse was not being loaded to the correct value.

Comments welcome.


 Return to top of page · Post #: 2 · Written at 5:30:51 PM on 19 September 2019.
GTC's avatar
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6367

Good idea. I don't do televisions myself, but I like reading diagnosis and repair stories nonetheless.

 Return to top of page · Post #: 3 · Written at 6:48:58 PM on 19 September 2019.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 1039

Hi Wayne, yes a good idea!
One of the most important aspects of the Serviceman's essays was the clear language used and the solid background of theory.
None of the episodes contained waffle (one of my downfalls!) and I still take pleasure in reading the old articles for the clarity of expression.
Your above story is good, I could understand it, so keep up the idea.
Remember don't divert the thought stream with extraneous detail, start off with the fault, then the diagnosis process and the cure, which is pretty much what you have done. Humour is good but stick to the story (let me do the jokes!) so the thought stream does not get polluted.

I'm always ready to learn from guys that know more than I do, so look forward to more stories of typical fixes.
Cheers, Fred.

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