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Old 17th Jan 2021, 7:59 pm   #41
ChristianFletcher
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Default Re: My First Television Set Stella

Thanks Lawrence. I suspect getting this far was the easy bit not sure what to do next maybe try my standard converter. I totally rebuilt the Cossor it had been slightly on fire. But not sure if I built it right first time I have tried it. Lots of twerking so perhaps capacitors. This is we’re we need video in the upload options. TVs been on for about an hour everything looks ok no burning smell after the valves warmed up.
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Old 17th Jan 2021, 8:37 pm   #42
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Question Re: My First Television Set Stella

That's looking great Chris, will be good to see a test card on it. I'd say you won't have much more to do with it, other than maybe a few resistors around the frame stage although it looks fairly linear.
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Old 17th Jan 2021, 8:43 pm   #43
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Default Re: My First Television Set Stella

Thanks John. I was thinking of trying to use this set as a learning tool so I want to hook a scope up and start looking at video waveforms and sync pulses. I don’t feel comfortable with it yet TVs are really complicated compared to radios. I hoping when I put up a video people can comment on the picture and what circuits need investigate etc.
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Old 17th Jan 2021, 11:14 pm   #44
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Default Re: My First Television Set Stella

looking good. Not far to go now!
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Old 18th Jan 2021, 8:24 pm   #45
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Default Re: My First Television Set Stella

https://youtu.be/oQ4VwXm2GQ4

Update link above to see my first test card. I think its now time for me to start reading the books. I am not exactly sure what I am seeing on the screen. I think I see very visible retracing at the top of the screen and a problem with the hold. I have so far only changed out the boost capacitor. It would be helpful to have a technical description of what I am seeing on the screen

I don’t want the problem fixed for me as I won’t learn anything. But it would be useful to have some ideas of how to start diagnosing the problem. Should I start looking at the video waveform to see how they look compared to the manufacturers data. I’m thinking I should be looking at the multivibrator and frame output and sync separator.

Thanks regards Chris
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Old 18th Jan 2021, 8:37 pm   #46
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Default Re: My First Television Set Stella

The capacitors in the frame stage will likely be causing the issue with the rolling. Nice looking picture, are you using an attenuator on the Aurora ?
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Old 18th Jan 2021, 8:57 pm   #47
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Default Re: My First Television Set Stella

No I’m not using an attenuator, should I be? The picture was also rolling on my two pattern generator. Having said that it was better on the cossor that does have an attenuator control.

Thanks Regards Chris
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Old 18th Jan 2021, 9:00 pm   #48
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Default Re: My First Television Set Stella

The attenuator wont stop it rolling, that's most likely to be the capacitors.
An attenuator is needed as the Standards convertor signal output is very high and can overload most sets.
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Old 18th Jan 2021, 9:18 pm   #49
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Default Re: My First Television Set Stella

Ok thanks, I will pick up some attenuators I didn’t know about overloading. Is there a typical attenuation factor I see I can get fixed -6db or variable -5 to -20db

Chris
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Old 18th Jan 2021, 9:59 pm   #50
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Default Re: My First Television Set Stella

Quote:
Originally Posted by ChristianFletcher View Post
I was thinking of trying to use this set as a learning tool so I want to hook a scope up and start looking at video waveforms and sync pulses.
Hi Chris,
I think that's a great idea. It's most instructive to get used to seeing things like the video waveform on a 'scope. Just being able to drive a 'scope and know what it is you are actually seeing is a skill in itself.

There were quite a few decent books from the era describing exactly how all the different bits of a TV worked and why the 405 video waveform was the way it was.

I've just watched your video and the first thing that struck me is what a superb picture you have! Tube looks first class and the frequency gratings on the test card look perfectly resolved. You have a classic case of no vertical sync pulses, so the vertical oscillator is just free running. By careful adjustment of the vertical hold you can either make the picture roll slowly up or down. As it's not 'locked', the frame flyback lines will not be blanked out and you can clearly see them.

Normally, in a correctly operating set, the vertical hold can be rotated quite a long way without the picture loosing lock- the sync pulses keep the oscillator at exactly the correct frequency.

So I would be looking at the sync separator stage. I don't doubt, if you change enough components you'll cure the fault, but it's much more instructive to find out what's going on with the 'scope and much more fun too!

I have been following this thread (honest!), but I can't remember if you are using an isolation transformer? It's essential if you want to connect a 'scope but why?

Well, the case of the 'scope and hence the 'earth' lead of the 'scope probe is connected to mains earth. The chassis of the TV is connected to mains neutral, so if you connect the two together, if there is an RCD protecting your mains supply, the RCD will trip when you connect the 'scope probe to the chassis. RCD's don't like earth & neutral being connected together! The isolation transformer separates the TV chassis from neutral and the RCD doesn't trip.

So I would read up about the 405 video waveform and familiarise yourself with what it should look like and then see if you can see it on your 'scope. Are you used to using a 'scope?

For faultfinding with a 'scope, test card 'c' really isn't that useful- the video part of it just looks a mess on the 'scope. A greyscale bars pattern is much more useful. Each bar produces a distinct line and so the video part of the waveform looks like a staircase on the 'scope. This makes it much easier to trace through the TV circuits and to spot any distortion.

Hope that might help,
All the best
Nick
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Old 18th Jan 2021, 10:30 pm   #51
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Default Re: My First Television Set Stella

Hello Nick

Thank you so much for that brilliant explanation it really helps me a lot to understand what your saying. Yes your spot on I can almost get the vertical to hold but it then starts to roll again so I guess the frame information going of sync with oscillator as they are not locked together at the moment. That would make sense.

You know I have always said that TV engineering really know their way around a scopes delayed sweep and time base options. I’m no expert on scopes but a deep memory on a modern Scope compensates for my lack of skill. Yes I do use an isolation transformer when working on live chassis but I have to say I don’t often use a scope on radio so it will be a first for me.

I have actually bought a few old service books but these do jump in by explaining how the individual circuits work in very great detail. I’m at the stage of just wanting a basic overview of how a television works. I’m not going to beat myself up I’m only on day two of television repair school.

Thanks again regards Chris
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Old 18th Jan 2021, 11:38 pm   #52
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Default Re: My First Television Set Stella

the lines look to me like frame foldover at the top, judging by the way the linearity runs out of whack up there. I think this will show a great picture before long!
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Old 18th Jan 2021, 11:53 pm   #53
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Default Re: My First Television Set Stella

As Nick has just said above, your weak frame sync is probably due to a fault in the sync separator stage. Not wanting to say too much and spoil your fun, I would be checking voltages around the sync seperator valve paying special attention to valve electrodes fed by high value resistors. Great picture so far. Tube looks as good as new.

Alan.
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Old 19th Jan 2021, 12:10 am   #54
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Default Re: My First Television Set Stella

Thanks for everyone’s comments and contributions to get me this far. I’m trying not rush into things and take a little time to build a foundation. But there is a lot to learn and it takes time and practice like most things. Looking forward to plugging my scope in I’m hoping I will be able to see a gray scale on the output from the Labgear pattern generator. I’m guess it’s much more unstable than the Aurora so that’s why the picture was even more distorted. My Labgear and the Cossor pattern generator were both total rebuilt by me so I’m not sure how good they are. The Labgear also has a 625 line output that look kind of ok on a modern CRT television but not great. I probably need to try and get some different test patterns.
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Old 19th Jan 2021, 12:16 am   #55
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Default Re: My First Television Set Stella

Quote:
Originally Posted by ChristianFletcher View Post
I have actually bought a few old service books but these do jump in by explaining how the individual circuits work in very great detail. I’m at the stage of just wanting a basic overview of how a television works. I’m not going to beat myself up I’m only on day two of television repair school.
Hi Chris,
Yes, I know what you mean- some books are way over the top and go into far too much detail. At this stage, you need a basic block diagram of the different TV stages and how they fit together, plus a good picture of a 405 video waveform showing the horizontal sync pulses.

What books have you managed to get hold of?

Actually, you don't need anything particularly fancy 'scope wise for almost everything you need to do on a TV or VCR. My old Gould 'scope from the '70's has a delayed timebase but I've never needed to use it! It's served me well over many years repairing TV's & VCR's. It does have 'TV triggering' which really helps though.

Do you have one of these fancy new digital 'scopes with an LCD display or a traditional CRT type one?

It sounds like you are pretty well set up if you have a 'scope, books, iso transformer, standards converter & pattern generator. Have you got anything that will generate a greyscale bars pattern?

Ah, just seen the pictures in post#39- you've got a proper workshop too! The disturbance in the middle of the picture of the cross hatch pattern from the Labgear is because the frame is not locked. The picture is probably rolling but you can't tell with that pattern. It will be interesting to spend some time playing with the 'scope & pattern generator, you don't need to involve the TV at this stage.

Cheers
Nick

Last edited by 1100 man; 19th Jan 2021 at 12:30 am. Reason: even more text added!
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Old 19th Jan 2021, 11:40 am   #56
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Default Re: My First Television Set Stella

Great picture!

This old book has helped me a lot in the understanding and troubleshooting of sync/line separator stages. Eventhough it is for US sets, the principles still apply:
https://worldradiohistory.com/BOOKSH...golis-1967.pdf

Also, I was kind of puzzled when looking for the boost capacitor in the LOPT section for your set. It should be connected to the anode of the PY81 somehow, and it usually has a value between 22 and 100 nF.

/Kind regards, Troels
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Old 19th Jan 2021, 12:23 pm   #57
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Default Re: My First Television Set Stella

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Originally Posted by staticmind View Post

Also, I was kind of puzzled when looking for the boost capacitor in the LOPT section for your set. It should be connected to the anode of the PY81 somehow, and it usually has a value between 22 and 100 nF.
Hi Troels,

Looking at the circuit in post#29, the boost cap is C609. It's not so much a case of it should be connected to the PY81 anode, but rather that one side of the boost cap connects to the HT rail. The PY81's anode also connects to the HT rail via the fuse, so yes, they are both connected together. The important point is that they are both connected to the HT rail.

I can't see what the value of C609 is but I would imagine it would be somewhere between 100nf & 470nf.

Cheers
Nick
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Old 19th Jan 2021, 12:46 pm   #58
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Default Re: My First Television Set Stella

Regarding the oscilloscope I have more that 17 at my last count from old valve scopes the size of a Fiat panda to modern high end stuff I use at work for debugging various serial buses. Although I have only recently come back to using scopes as for many years I was using logic analysers and for radio work a spectrum analyser is my tool of choice now. The large scope collection, putting work needs aside is because my first love is collecting and repairing test gear. Now interesting it was my two pattern generators that I refurbished and require a Television to test them on so interesting my interest in TV is very recent and probably explains my lack of knowledge repairing them.

Although I do a lot of work on microcontrollers and FPGA design I am not really interested in modern electronics in my home time project.

I have included a picture of the several books I have on Television repair and I am just reading them again as it makes a difference having some context regarding learning

Thanks (staticmind) for the book on solving sync issues the beginning of the book gives a good explanation regarding my lack of vertical hold and the problem I’m encountering

As other have commented It will be interesting for me to start looking at the video waveform now in more detail.

I’m also looking into to using a DVD player to provide some vertical bar and grey scales via the Aurora. There are some links on the forum to burning CDs with ISO image test patterns. I am going to have ago at that but I have never been very successful at transferring image burned on a computer CD to A dvd disk. There are some already done on eBay so I may just buy one of those.



Thanks regards Chris
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Old 19th Jan 2021, 2:55 pm   #59
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Default Re: My First Television Set Stella

Excellent choice of books. John.
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Old 24th Jan 2021, 10:25 am   #60
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I haven’t done any more work on the television since my last post but I have uploaded the first power and some extended sequences showing the screen and the issue with the vertical hold circuit. Hopefully this week I will be taking a closer look at the sync separator and the various waveform. You will also see that the advice previously given to change out the boost capacitor was spot on Thanks. https://youtu.be/kQdlDwxMbGo

Chris
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