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Old 26th Mar 2019, 6:20 pm   #41
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Default Re: PIL - Colour fringing

Quote:
I was thinking about wearing gloves
Could lead to a false sense of security (and less dexterity), dry floor, left hand in pocket (jam it in) and caution is better. Do it standing up too, if by very remote chance you get a shock you will fall down breaking the circuit.
 
Old 26th Mar 2019, 6:37 pm   #42
ms660
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Default Re: PIL - Colour fringing

You'll have a job adjusting the yoke or it's rings with one hand, generally a two hands job with power on, static convergence and blue lateral can be done with one hand with a delta tube, but purity is usually a two hand job with those as well.

Lawrence.
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Old 26th Mar 2019, 10:33 pm   #43
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Default Re: PIL - Colour fringing

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Originally Posted by 19Seventy7 View Post
if I could take up Julie's offer of the BASIC programme, please? I'd be grateful as I could use "Beeb Emulator" to programme it in and I'll get a suitable adaptor/cable to connect my PC to the TV.
The idea was to use an actual 1980s computer which will plug straight into the RF input of the set. If you're going to use a PC with some kind of VGA to composite converter and a modulator or VCR, then you could probably do a better job natively on the PC with some graphics editor or other, then set it going in a slideshow on full screen with a really long delay and use the arrow keys to select a picture ..... but anyway, I just banged this out in Beebem:
Code:
   10MODE4
   20M%=3
   30S%=64
   40IF M%AND1 PROCHB
   50IF M%AND2 PROCVB
   60K$=GET$
   70IFK$>="0"ANDK$<="7" VDU19,1,ASCK$AND7;0;:GOTO60
   80IFK$="H" M%=1
   90IFK$="V" M%=2
  100IFK$=" " M%=3
  110CLS
  120GOTO40
  130DEFPROCHB
  140FORY%=0TO1023STEPS%
  150MOVE0,Y%:DRAW1279,Y%
  160NEXTY%
  170MOVE0,1023:DRAW1279,1023
  180ENDPROC
  190DEFPROCVB
  200FORX%=0TO1279STEPS%
  210MOVEX%,0:DRAWX%,1023
  220NEXTX%
  230MOVE1279,0:DRAW1279,1023
  240ENDPROC
Instructions:

Press number keys to select colours: usual BBC colour numbers, i.e. 1=red 2=green 3=yellow 4=blue 5=magenta 6=cyan 7=white. Press H for just horizontal bars, V for just vertical bars, space for full grid, Escape when done.

I hereby relinquish all copyright in this code and dedicate it to the Public Domain.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
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Old 26th Mar 2019, 11:34 pm   #44
Lucien Nunes
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Default Re: PIL - Colour fringing

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Would it be possible, if you had the time and patience to do so, but get an almost perfect convergence, if not perfect?
Not necessarily. As Sideband says:

Quote:
There was also a degree of 'acceptable error' which applied to any domestic TV.
Unlike an LCD where geometry, purity and convergence are inherently perfect and unchanging, CRT dynamic convergence (especially) involves a lot of compromises and variables, any of which might be impossible to get right on any particular specimen of tube. Domestic TV CRTs, yokes and the circuitry driving them were made to meet a specification and this always allowed wider tolerance on corner convergence because it's both harder to achieve, and least noticeable. That's also why the ident is in the corner.

I used to look after a fleet of professional video monitors that often needed CRT adjustment / replacement as they had a hard life travelling the world. One factor that you learn with experience is strategy. When to carry on tweaking multipoles, when to backtrack and start again with the DY position because the convergence is screwing up the purity, when to stop poking around with permalloys and accept that the tube is a less than perfect example that simply can't be got any better, and when to accept that the result is in-spec and the law of diminishing returns is about to deprive you of a tea-break unless you put the back on and send it on its way.
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Old 27th Mar 2019, 1:15 pm   #45
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Default Re: PIL - Colour fringing

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Originally Posted by merlinmaxwell View Post
Quote:
I was thinking about wearing gloves
Could lead to a false sense of security (and less dexterity), dry floor, left hand in pocket (jam it in) and caution is better. Do it standing up too, if by very remote chance you get a shock you will fall down breaking the circuit.
Hi,
I wouldn't let my guard down if wearing gloves, I know that there's still risks even with gloves, but they'd be there as an extra safety line. I'd need to stand up too, the TV would have to get moved to the kitchen counter or the dining table as it's stand is too low down.

Quote:
You'll have a job adjusting the yoke or it's rings with one hand, generally a two hands job with power on, static convergence and blue lateral can be done with one hand with a delta tube, but purity is usually a two hand job with those as well.
Will the purity get "knocked" when adjusting the DY? It's very clear, I can't notice any blotching so that can be left alone if possible. I suppose i'll see either way what's happening.

Quote:
The idea was to use an actual 1980s computer which will plug straight into the RF input of the set. If you're going to use a PC with some kind of VGA to composite converter and a modulator or VCR, then you could probably do a better job natively on the PC with some graphics editor or other, then set it going in a slideshow on full screen with a really long delay and use the arrow keys to select a picture ..... but anyway, I just banged this out in Beebem:

Hi, I never thought of that! I don't have a 1980s computer, so of course couldn't but I have got beebem. I did once try getting my Xbox to show a grid pattern, but failed to get a full screen grid.

Thanks for that code, anyway! I might still end up using it if I can't get a proper grid elsewhere.

Quote:
Unlike an LCD where geometry, purity and convergence are inherently perfect and unchanging, CRT dynamic convergence (especially) involves a lot of compromises and variables, any of which might be impossible to get right on any particular specimen of tube. Domestic TV CRTs, yokes and the circuitry driving them were made to meet a specification and this always allowed wider tolerance on corner convergence because it's both harder to achieve, and least noticeable. That's also why the ident is in the corner.
That's quite understandable, I just thought if it relied on precise positioning of the DY, then the convergence could be just as precise. Maybe not. This is just me being a little OCD, but I completely understand that CRTs aren't as precise as LCDs.

Of course my set could be like you say, can't get any better. Hopefully it can, as it could potentially straighten out the wonky picture.

Fingers crossed some improvement can be made

Thank you all for your help! I really appreciate it!
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Old 27th Mar 2019, 1:47 pm   #46
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Default Re: PIL - Colour fringing

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Originally Posted by 19Seventy7 View Post
Will the purity get "knocked" when adjusting the DY?
Only you can answer that.

Make sure you use a decent mirror and that both you and the set are comfortable.

Good luck whicheverways.

Lawrence.
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Old 27th Mar 2019, 2:10 pm   #47
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Default Re: PIL - Colour fringing

Fair enough

Will do, I've got a pretty big mirror I can use which should do the job.

Thanks
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Old 27th Mar 2019, 7:26 pm   #48
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Default Re: PIL - Colour fringing

Could you not just use the test card DVD available in the stickies? Assuming you have the means to burn a disc you could play this on a DVD player via a VCR into the aerial socket.

Does the BBC computer allow writing to the edges of the screen? I know other 8 bit computers had a fairly large border that couldn't be written to.
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Old 27th Mar 2019, 9:43 pm   #49
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Default Re: PIL - Colour fringing

Hi,

I have just looked into them and could possibly try. I've been looking for ages for some blank DVDs but cannot find any anywhere. I could get them online, but I don't want to spend money which I don't really have on a pack of DVDs, and just use one or two. I might have a wire somewhere to connect my PC to my VCR to use the Beebem, which is why I went with the BASIC idea.

Thanks
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