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Old 19th Mar 2019, 11:04 pm   #1
19Seventy7
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Default PIL - Colour fringing

Hi,

I have a 1970s Hitachi CTP-213 TV, which is a PIL set. The service manual says that it is a self convergence set. I have noticed that whites have a blue and red surround. Especially to the upper left corner.

I also have a wonky image on the screen, and I was told by a forum member that PILs convergence relies on the deflection yoke, which also controls the tilt of the picture. I was also told that the yokes were firmly stuck. But I'm now wondering if the yoke has been messed around with in the past.

The picture is of the BBC water mark seen in the top LH corner. The colour fringe is noticeable further away than the distance in the photo.

Any help is greatly appreciated.

Thanks
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Old 19th Mar 2019, 11:21 pm   #2
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Default Re: PIL - Colour fringing

There are different types of inline crts, from memory the Hitachi crts from the middle to later 70’s relied on precision positioning of the scan coils. They had wedges that fitted between the scan coils and the glass bowl of the CRT.
If it is this type of crt and the wedges are missing the scan coils will be in tbe incorrect position and have faulty registration.

CRT’s such as the Mullard 30AX required no adjustments.

Is there any information in the manual about scan coil adjustments?
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Old 19th Mar 2019, 11:30 pm   #3
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Default Re: PIL - Colour fringing

Hi,

Thanks for a quick reply

I believe that this set relies on the position of the scan coils, and there are wedges, but they look to be taped down. I don't know if this is a manufacture technique or they were once removed and taped back down.

I'm only looking at past photos at the moment, but I can open up the back tomorrow for a better look. I have a photo attached (sorry for the quality, but it's zoomed in from another photo) which might help

Thanks
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Old 19th Mar 2019, 11:41 pm   #4
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Default Re: PIL - Colour fringing

It is possible that the wedges have sagged a little bit.
They will not be far off.
If you can find a wedge from a bashed up set in a pile of fly-tipped waste try it in along side the existing one.
There is usually three.
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Old 19th Mar 2019, 11:46 pm   #5
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Default Re: PIL - Colour fringing

I think there is three or four, i'll have a look tomorrow and see if they've sagged or moved. Could this help out, or even sort, the wonkiness of the picture, too?

i'll have a look around town tomorrow to see if I can find any old sets (I doubt I will, though I think I might know a place)

Thanks for your help
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Old 20th Mar 2019, 12:40 am   #6
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Default Re: PIL - Colour fringing

If you have the service manual it should document how to set up the CRT.
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Old 20th Mar 2019, 1:36 am   #7
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Default Re: PIL - Colour fringing

I have the service manual, and it has a section for "connection for alignment" so could this possibly be it?

It looks as if it shows what needs to be altered to adjust, I could be wrong though.

Thanks
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Old 20th Mar 2019, 10:44 am   #8
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Default Re: PIL - Colour fringing

Hello 16sevety7.

I can see from your question and last post that you are new to TV servicing.

We all started this way and so much of the experience gained will now be second nature. This includes that colour television is a monochrome set with added cicuits to provide a coloured picture.

Your last post which, should you trace the image back to the block diagram, which shows how the set was designed, is of the chroma board. It has nothing to do with converging the red, green and blue electron beams on the CRT.

I am sure that somewhere there a detailed instruction of how to align the deflection yoke on this sets pre converged PIL tube but I can't find it just now. It requires the deflection yoke to be tlited in specific directions to converge the display.

What I can tell you is that without such instructions, trial and error is possible, but you will need to also know that very high voltages are present on the deflection yoke and you should take the necessary precaution.

Remember also that the yoke will have been fixed in position mechanically on the neck of the CRT after the wedges have been inserted.


Chris
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Old 20th Mar 2019, 11:28 am   #9
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Default Re: PIL - Colour fringing

Hi Aaeron,
The scan coil assembly is considered part of the CRT and is fitted and aligned by the tube manufacturer. It's adjusted by the wedges and then held in place by copious quantities of glue. It's very unlikely to have moved over the years.

A replacement tube would come with the coils already attached; the service technician would not be expected to fit & align them. Therefore it's unlikely that there will be any alignment information in the service info.

In order to make any adjustments, you would have to completely un-stick the coil assembly which would completely upset all the adjustment. There is no saying then that you would be able to get things any better than they are now.

Plus you will have to do it while watching a grid pattern on the screen in a mirror from behind the set. Obviously the set has to be on, so you are working with your hands on the scan coils which have very high pulse voltages on them which will bite!

PIL tubes were very far from perfect and were only expected to be 'acceptable' from a normal viewing distance. Generally colour fringing was masked by the colour picture!

Programs at the time would not have contained small graphics like the BBC logo which make the problem look worse.

So my advice, as it has been in the past, is leave it alone!!

Top marks to you though for being interested enough to want to have a go!

All the best
Nick
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Old 20th Mar 2019, 1:50 pm   #10
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Default Re: PIL - Colour fringing

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Originally Posted by simpsons View Post
Hello 16sevety7.

I can see from your question and last post that you are new to TV servicing.

Your last post which, should you trace the image back to the block diagram, which shows how the set was designed, is of the chroma board. It has nothing to do with converging the red, green and blue electron beams on the CRT.

I am sure that somewhere there a detailed instruction of how to align the deflection yoke on this sets pre converged PIL tube but I can't find it just now. It requires the deflection yoke to be tlited in specific directions to converge the display.

What I can tell you is that without such instructions, trial and error is possible, but you will need to also know that very high voltages are present on the deflection yoke and you should take the necessary precaution.

Remember also that the yoke will have been fixed in position mechanically on the neck of the CRT after the wedges have been inserted.


Chris
Hi,

That’s right and it most likely shows, too! Haha

Ah, okay. I just saw the “alignment” part and what looked to be a pot which i thought could be twisted to align the electron beams to their respective phosphors

The service manual doesnt have any information on convergence. The closest was the “connection for alignment” diagram.

I do know about the high voltages inside and so, if i do have the back off, 9 times out of 10, its been unplugged and switched off for a while, but i still take precautions.

Thank you for your help, it’s really appreciated!
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Old 20th Mar 2019, 1:59 pm   #11
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Default Re: PIL - Colour fringing

Hi

This type of flaring also depends on how high the user controls are set. Usually much worse if colour and brightness are turned up all the way.

Convergence results also differ slightly depending on which way the tube is facing during convergence. I believe East/west facing tube at alignment produces better results than north/south alignment.

The deflection coil has its purity set up first, then convergence, there are two types of convergence- static (centre of the screen) and dynamic (edges of the screen). Static usually being set up accurately and dynamic is a bit of a compromise as you usually aren't concentrating on the edge of the picture.

When the set is made a green raster is displayed, a camera then is placed on the centre of the screen. An operator then pushes the DY forward and rotates it back and forth until the 'landings' are correct. This is usually just a bar graph display with the information taken from the camera attached to the front of the screen. Once correct the DY is screwed into place.

There may be some adjustable 'rubbery' rings behind the DY, the first two nearest the DY effect purity adjustment, all the other rings adjust convergence. once set up these are covered in a varnish so they cant be moved. Screen edge adjustments are then made with rubber wedges.

As others have said, the wedges could have shrunk or sagged a bit over the years so any convergence errors have increased slightly, but years ago idents for broadcasters were not transmitted all the time, so any errors wouldn't have been noticed until they got really bad.

Cheers

Mike
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Old 20th Mar 2019, 2:20 pm   #12
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Default Re: PIL - Colour fringing

Quote:
Originally Posted by 1100 man View Post
The scan coil assembly is considered part of the CRT and is fitted and aligned by the tube manufacturer. It's adjusted by the wedges and then held in place by copious quantities of glue. It's very unlikely to have moved over the years.

A replacement tube would come with the coils already attached; the service technician would not be expected to fit & align them. Therefore it's unlikely that there will be any alignment information in the service info.

In order to make any adjustments, you would have to completely un-stick the coil assembly which would completely upset all the adjustment. There is no saying then that you would be able to get things any better than they are now.

Plus you will have to do it while watching a grid pattern on the screen in a mirror from behind the set. Obviously the set has to be on, so you are working with your hands on the scan coils which have very high pulse voltages on them which will bite!

PIL tubes were very far from perfect and were only expected to be 'acceptable' from a normal viewing distance. Generally colour fringing was masked by the colour picture!

Programs at the time would not have contained small graphics like the BBC logo which make the problem look worse.

So my advice, as it has been in the past, is leave it alone!!

Top marks to you though for being interested enough to want to have a go!
Hi,

That’s understandable. Of course i know very little compared to many other forum members, so i thought best to ask.

Even if very unlikely, could there not be a chance of the rubber wedges perishing, or cracking or something which could make them lose grip of the yoke?

With the grid pattern, i couldnt do that as i cannot get a grid pattern, unless i bought a DVD or something with it on. Of course, i’d take precautions before and during any process involving electronics.

That makes sense again, it’s just that it can make fine text harder to read, which i assume back in the 70s and 80s wouldn’t have been common either. I only really notice it on text and those little graphics. When a full screen picture is on it’s fine and not noticable at all.

I’ll leave it well alone. I don’t want to mess it up and ruin it.

Thank you for your help, it’s really appreciated too!
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Old 20th Mar 2019, 2:32 pm   #13
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Default Re: PIL - Colour fringing

Quote:
Originally Posted by ekcopyephilips View Post
This type of flaring also depends on how high the user controls are set. Usually much worse if colour and brightness are turned up all the way.

Convergence results also differ slightly depending on which way the tube is facing during convergence. I believe East/west facing tube at alignment produces better results than north/south alignment.

The deflection coil has its purity set up first, then convergence, there are two types of convergence- static (centre of the screen) and dynamic (edges of the screen). Static usually being set up accurately and dynamic is a bit of a compromise as you usually aren't concentrating on the edge of the picture.

When the set is made a green raster is displayed, a camera then is placed on the centre of the screen. An operator then pushes the DY forward and rotates it back and forth until the 'landings' are correct. This is usually just a bar graph display with the information taken from the camera attached to the front of the screen. Once correct the DY is screwed into place.

There may be some adjustable 'rubbery' rings behind the DY, the first two nearest the DY effect purity adjustment, all the other rings adjust convergence. once set up these are covered in a varnish so they cant be moved. Screen edge adjustments are then made with rubber wedges.

As others have said, the wedges could have shrunk or sagged a bit over the years so any convergence errors have increased slightly, but years ago idents for broadcasters were not transmitted all the time, so any errors wouldn't have been noticed until they got really bad.
Hi,

I’m not sure how high the brightness and colour are set. I know i adjusted them as i was playing a tape with odd colours, so i adjusted to compensate. This could explain a lot because i did think it had got a little worse than it used to be. I’ll power the set up and see if adjusting them helps.

The graphic with the fringing, is at the edge of the screen which makes sense if they were comprimised. It makes sense, though.

It would make sense then, that the wedges which could’ve perished a little, as its effects are what i see on my screen. It’s mainly noticeable when watching older TV programmes which have the black bars down the side and then the white graphic on a black background makes the colours more noticable.

Thanks for your help, i really appreciate it!
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Old 20th Mar 2019, 2:42 pm   #14
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Default Re: PIL - Colour fringing

There was also a degree of 'acceptable error' which applied to any domestic TV. If this was a computer monitor, the errors would be far less. Everything said so far is correct and the deflection yolk is 'married' to the tube during manufacture. There won't be any convergence instructions. The 'acceptable error' was basically that the centre part of the picture (the area of the test card circle) should be near perfect and the worst errors should be in the corners where they are least disturbing. As the tube ages, the focus deteriorates making the errors look worse.

Leave it as it is!! Attempting to try and improve matters by fiddling with the wedges and the rings around the neck of the tube will probably just make things worse.
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Old 20th Mar 2019, 3:51 pm   #15
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Default Re: PIL - Colour fringing

Hi,

As you say, the centre is absolutely fine, it’s the edges that have the issues. Id think that monitors have to have less errors as you‘d be sitting closer and would then see the errors easier.

I have left it alone apart from taking note of what Mike said about colour and brightness. I’ve re-adjusted these and the fringing is less noticable, and fined fext is easier to read!

Thank you all for your help! I really appreciate it!
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Old 20th Mar 2019, 10:12 pm   #16
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Default Re: PIL - Colour fringing

Quote:
Id think that monitors have to have less errors as you‘d be sitting closer and would then see the errors easier.
The tubes were of better quality with a much finer 'slot pitch' for high resolution graphics.
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Old 20th Mar 2019, 10:26 pm   #17
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Default Re: PIL - Colour fringing

Ah alright, were these then used on the HD CRTs from the 2000s?

Thanks
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Old 20th Mar 2019, 10:37 pm   #18
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Default Re: PIL - Colour fringing

I only ever did the convergence on one TV set, because I was scared of EHT and live chassis as were common in the days when I passed up so much easy money. I fixed the set but the red, green and blue components of the picture were all over the place. I used either a BBC Micro or a ZX Spectrum (can't remember which), running a BASIC program I typed in, as a makeshift test pattern source. I remember I had it so pressing the number keys changed the colour of the lines to activate different combinations of the electron guns. The screen was over 50cm. and there was some tearing towards the edges that I could not get rid of altogether, but actual programmes looked OK on it.
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Old 21st Mar 2019, 1:39 am   #19
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Default Re: PIL - Colour fringing

Quote:
Originally Posted by 19Seventy7 View Post
I do know about the high voltages inside and so, if i do have the back off, 9 times out of 10, its been unplugged and switched off for a while, but i still take precautions.
Please don't rely on leaving a set switched off for a while as a way of rendering it safe to work on.

There are electronic parts which can keep a dangerous charge for quite a while. You really need to know more about circuitry with high voltages in it, and how to make it safe, before you start working on it.

Please don't take this the wrong way - I am worried about your safety! In fact, when I think back to some of the 'experiments' I used to perform in my younger days, I'm surprised I only got a few, survivable, shocks!

You're obviously keen and that's great. But please remember that electricity is a wonderful servant, but a terrible master.
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Old 21st Mar 2019, 3:55 am   #20
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Default Re: PIL - Colour fringing

Hi,

I don’t just rely on the set being switched off for some time. This is just one of the things I do beforehand. When I did have the back off, i’d never touch the CRT for my sake, and its own sake. I have only had the back off once with power applied to the set as I had to see what happened to the screen. I followed the hand-in-the-pocket rule, rubber soled shoes, too.

I’d think that there is more steps to take before i get my hands in a set again, but i’m not to sure of what to do, and if i can do them (discharging - I don’t know how to do that) Looking back to when i first opened it up, I realise how much more I should’ve done, I guess I was lucky that I didnt get shocked.

Don’t worry, I haven’t taken this the wrong way at all. I’d much rather be told what to do and what not to when it comes to something like this, again for my sake and the set in question.

Thank you for your concerns, and also for your help! Again - I really appreciate it!
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