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ITT CVC8 set 2

 
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Re: ITT CVC8 set 2

Post by freya » Wed Nov 25, 2015 6:17 pm

Couldn't resist trying the new Leader LCG-399A pattern generator, even though the set is currently in the garage.
Needless to say the colour is a real mess along with the convergence. Will upload some pictures as soon as its inside and up to room temperature. Its going to need expert guidance for me to get this right I think.

 
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Re: ITT CVC8 set 2

Post by crustytv » Wed Nov 25, 2015 10:32 pm

Technically all the information you will require on convergence can be found on the main site here.

In reality I've come to find there is no substitute for just getting on and doing it. I suspect this was true back in the day when sets were being rolled out, the service engineers would be exposed to the task on a regular basis. I've certainly found the more I do it the more success I have. However I would add that it takes me ages to get the results compared to the likes of Malc, John and Gary.

If its well out of whack then its probably safe to centre all the pots and take it as a fresh installation.

Good luck and enjoy the eye popping fun that lays ahead.

 
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Re: ITT CVC8 set 2

Post by Terrykc » Thu Nov 26, 2015 12:25 pm

Never, ever, jump to the conclusion that poor convergence is simply a case of suitable adjustment to correct it. 

It is important to always degauss the set and check/adjust purity before touching any convergence adjustments. If only degaussing is required, you may find that convergence errors magically disappear after it is done - though this will be rare.

Some sets are particularly prone to changes in the earth's magnetic field and, if you are unlucky enough to encounter one of these, you may find it necessary to carry out all adjustments with the set in the position in which it is to be used. Again, thankfully, this is rare but should be borne in mind.

If you are new to colour, there is a possible hazard lying in wait for the unwary - the workshop environment!

Is there any ferrous metal on, under or around your work bench or other work place? Any Dexion Angle, steel cased component storage, steel drawers and cupboards? Any of these could be magnetised to a greater or lesser extent and play havoc with your efforts. 

Do you have a test speaker on your bench? Does it have a closed magnetic field? Keep it as far away a possible until you have successfully set up your first colour set and only then bring it closer to the set to see if it has any undesired effects.

The  degaussing circuits in the average set are very good for keeping the occasional magnetic field at bay but, for anything serious, including external fields from the aforementioned ferrous objects, then only a proper degaussing tool will do the trick - although these are likely to be hard to find, these days.

Of course, it won't be easy to know if any of these hidden problems exist in your particular environment but you should bear them in mind.

Set up the purity and then, with a red raster, move the set about and turn it round. If the raster displays any signs of impurity, you may well have a problem. If it doesn't you can breathe easily and get on with the full set up!

 
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Re: ITT CVC8 set 2

Post by freya » Thu Nov 26, 2015 2:31 pm

Here are a few pictures, nothing has been adjusted yet. New positor has been fitted but there still appear to be patches "purity" ? old positor was full of rattles and bits.
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Re: ITT CVC8 set 2

Post by nuvistor » Thu Nov 26, 2015 2:56 pm

there seems a lot of moire patterning on the picture, unless it is patterning from the RF/IF stages.
As for purity what is it like with the red only gun?

Frank

 
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Re: ITT CVC8 set 2

Post by freya » Thu Nov 26, 2015 3:40 pm

Sorry, should have said the moiré is a camera artefact.
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Re: ITT CVC8 set 2

Post by nuvistor » Thu Nov 26, 2015 4:11 pm

If you have no degassing coil, hopefully the auto will have cleared any magnetism up. Bearing in mind Terry's advice you can start the setup, may even be worth turning the set around to see if the purity changes before any adjustments are made.
Frank

 
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Re: ITT CVC8 set 2

Post by Terrykc » Thu Nov 26, 2015 4:13 pm

At the risk of repeating myself:

Terrykc wrote:... It is important to always degauss the set and check/adjust purity before touching any convergence adjustments ...

As far as degaussing is concerned, now that the set's own degaussing circuit is working properly, you can use it for a sanity check.

Check the purity as before, then switch off.

When switching on again from cold, the degaussing circuit should come into action again - you should be a slight mechanical 'brrr' as the ferrous part s of the set, including the shadow mask inside the CRT, vibrate at mains frequency - and, on warm up, the purity errors (if any) should be exactly the same as before. If there is a change, repeat as necessary.

When the original Positor failed, there is a faint chance that the debris created when it disintegrated could have temporarily bridged some of the internal contacts giving a brief pulse of energy to the degaussing coils. The rapid collapse of the magnetic field at the end of the pulse would make the circuit work in reverse, actually magnetising the tube and the shield to a much higher level than the circuit is normally expected to overcome, thus repeating the operation might be necessary to completely degauss the set.

I know I'm probably going to extremes here but I'm trying to cover every possible situation that might occur.

The fist time you carry out the purity and convergence procedures you can expect to take quite a long time, so it is worthwhile making sure that your efforts won't be in vain - as you would find out the next time you turned on the set!

 
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Re: ITT CVC8 set 2

Post by freya » Thu Nov 26, 2015 4:30 pm

Can the degauss be checked ? its pretty silent on switch on. I always remember a transformer type thump sound from my childhood.

 
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Re: ITT CVC8 set 2

Post by rob t » Thu Nov 26, 2015 4:39 pm

If you dont have a degaussing coil you can use a gun type soldering iron .
turn it on a few feet from the set bring it sideways towards the face of the CRT and move it in a circular motion .
slowly with the iron still on move it away from the set (about 2 foot) befor turning it off.
Rob T

 
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Re: ITT CVC8 set 2

Post by freya » Thu Nov 26, 2015 4:47 pm

Thanks Rob, I used to have one but ditched it years ago now thinking "what would I use that for"
Now the embarrassing bit.....the de gause fuse was gone :ccg

 
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Re: ITT CVC8 set 2

Post by Terrykc » Thu Nov 26, 2015 5:43 pm

I've never heard of using a solder gun before - I wouldn't have thought it would have sufficient external field for the job.

One thing to remember about using an external degaussing coil is that the switch on and switch of pulses can be equally damaging so start a good distance away from the set - I'd recommend a minimum of six feet - and hold the coil edgeways on to the set (minimum field) when switching on.

Then approach the set, turning the coil flat side on to the set (maximum field), keeping the coil moving in a circular motion. Move the coil over the screen area whilst doing so, then along the top and down both sides, turning the coil to keep it flat side on to the set as you do so.

Return to the screen for one last circle then retreat from the set, keeping the coil moving all the time. 

When you have reached a safe distance - and not before - turn the coil edgeways on to the set again - no disturbance should be seen on the screen at this point, provided you are far enough away - before finally switching off.

Degaussing coils vary considerable - one we had from Baird resembled a steering wheel whilst the one sold by RBM was much smaller and resembled a discus. Both worked equally well!

By the way, expect a far bit of noise from the set whilst you are doing this - it is simply the shadow-mask and the external magnetic shielding vibrating in sympathy with the mains. 

That switch-on 'transformer thump' is probably a better description than mine, Stephen!

 
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Re: ITT CVC8 set 2

Post by Refugee » Thu Nov 26, 2015 6:23 pm

I have used a Weller soldering gun for degaussing VGA screens. I also have an old transformer that I took to bits and just put the E shaped lams back in and it also works well.
A TV engineer at a place I once worked at put his coil down upside down. The resulting burning smell informed him of his mistake as the button was pressing on the bench.

 
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Re: ITT CVC8 set 2

Post by Katie Bush » Thu Nov 26, 2015 10:36 pm

I remember our old degaussing coil.... It was four sections (or two full sets) of coils from a couple of scrapped G6's.. With all four sections wired in series and wrapped in PVC tape, a long, long lead to the mains plug came off the coils to a "push to make - release to break" in-line switch.

That coil set served my granddad for many years.. It worked beautifully, cost only pennies to make and reused old parts that would otherwise have ended up in tip.

Marion

 
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Re: ITT CVC8 set 2

Post by freya » Tue Dec 01, 2015 3:47 pm

So my first attempt at a complete setup of convergence and purity.
It seems miles better now, my only question is regarding the colour bars where the verticals meet each other there appears to be an effect which blurs or overlaps. Is this to be expected or something else to look at.
More pictues, sorry about moiré patterning :qq1
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Re: ITT CVC8 set 2

Post by nuvistor » Tue Dec 01, 2015 4:00 pm

looks good to me, congratulations, I would not worry about the trasistion on the colour bars, not sure if it the set or generator but was quite common. If it is noticible on standard TV programs have look for it but at normal viewing distances it should be ok.
Frank

 
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Re: ITT CVC8 set 2

Post by Cathovisor » Tue Dec 01, 2015 4:05 pm

That transition on the green/magenta bar is perfectly normal. At that point the colour subcarrier is making a 180° phase reversal so it's only to be expected. The only time you'll ever see perfect transitions at that point is in a monitor fed YUV or better still, RGB.

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