Adjusting the image in the original screen.

[||C|-|E||]

It is actually ready now 

[Bryce]

You seem to be really enjoying yourself there I suppose it's interesting as a "non-electronics person" to see how all the different magnets and coils effect the picture in different ways. As long as you are careful it's not difficult. Glad you were able to tune the picture to exaactly how you want it.
Yup, I forgot to mention in my step-by-step, that the metal of the screwdriver effects the adjustment. I use a ceramic screwdriver for stuff like this, but it's easy to compensate for the effect of a normal screwdriver, so there's no need to go and buy a special one just for a once off job.

Bryce.

[||C|-|E||]

It was cool but stressing, at least at the beginning  But now everything is much better, it actually looks very nice. There are two things that are still there, though. The first is certain amount of dirt I caused with my screwdriver. I removed most of it, but some remains in the upper right corner. I can make it disappear if I put a small neodymium magnet on top of the screen, but it does not seem a really elegant long term solution. I guess that I should consider to demagnetize it, but I do not have a degaussing coil here and they are a bit expensive  . When I received the screen that corner was already not completely perfect, but a bit darker than the rest, now it is yellowish. The second is that the screen could benefit of a very very slight correction of the dynamic convergence. This is almost not noticeable and I have seen the corners of almost all CRTs with a little bit of this problem, but still. I will not probably try it, it was there at the beginning and it seems very difficult to correct without messing with another region of the image. I know a guy that did it with an arcade screen using wedges and tape, but it took him a very long time...

[||C|-|E||]

Good news! I found that my uncle has at home (in Spain) a huge amount of NOS convergence yoke strips and a set of ceramic screwdrivers that he is not using anymore. So, I will take those with me and see if I manage to obtain a perfect image. In only need to:

a) Demagnetize the bloody thing, because that little tinting in the corner makes me nervous (although I could try to correct everything with a little magnet in the proper place, because that works very well)
b) Adjust a little bit the dynamic convergence with the strips (or at least try)
c) Ideally, I would adjust the H-size by a few pixels as well, but I do not find a resistor to do this, as in the case of the V-size, that was very easy. Is there anything like that or is it necessary to move the yoke? In that case I will let it as it is now.

[Gryzor]

I was afraid we weren't going to hear back from you

[Bryce]

H-Size isn't usually adjustable, it's controlled by the LA7800 and some fixed value parts. You can only really change it by changing the frequency of the H-Sync pulses.

Bryce.

[||C|-|E||]

It is fine then . It is just a question of few píxels. In the past this would not be noticeble because of the screen border. Nowadays, in the era of the overscan, is when you see everything .

@Gryzor. The first day you try to adjust something you never die, it is only when you feel more condifent that you die electrocuted in the most horrible way .

[1024MAK]

c) Ideally, I would adjust the H-size by a few pixels as well, but I do not find a resistor to do this, as in the case of the V-size, that was very easy. Is there anything like that or is it necessary to move the yoke? In that case I will let it as it is now.

For a few pixels, I'd leave it alone. For TV pictures on TVs, the idea is to overscan the image so there are no unused areas. For computer use, you may want a slight border ;-)

Mark

[||C|-|E||]

I will let it be then  . Let´s see if I manage to solve the rest of the things with the convergence strips. I will try to degauss it properly with a coil first (since I do not like the idea of letting a magnetic Pikachu o top of the screen forever) and then I will try with them. I guess that it will take a decent dose of patience, but it is fine. I prefer this approach than trying something risky that would probably screw the things up (like trying to adjust the purity and convergence from scratch completely unscrewing the yoke). With my lack of experience this would a recipe for disaster, so I think that is safer not to mess with the things much. For instance, yesterday I was trying to adjust the purity with the purity magnets but it is very easy to fix the problematic corner just to see that you are creating another issue somewhere else. At the end, I almost let them like they were from factory, but the difference was enough to improve the image.

A few years ago there was workshop in every corner able to do these kind of things, now they are very difficult to find and repairs are very expensive, either that or they tell you to throw the screen away 

[Dr Tiger Ninestein]

I know this isn't cpc related but I thought I'd ask here as this thread seems somewhat relevant.


My ntsc snes pushed my picture out to the left on my crt. Foolishly I messed around in the service mode without recording my original settings and now my picture is slightly wavy on either edge of the screen


Does anyone know which setting I need to adjust? I've spent ages tinkering with it now but none of the settings seem to straighten it up.

[Dr Tiger Ninestein]

By the way, I have no idea why every photo I post ends up upside down

[gerald]

By the way, I have no idea why every photo I post ends up upside down

If you're using a phone, just turn it. The Exif data says to turn the picture 180 deg, but the thumbnail does not.

[Dr Tiger Ninestein]

If you're using a phone, just turn it. The Exif data says to turn the picture 180 deg, but the thumbnail does not.

I'm using an iPad. I've tried turning it before but just keep getting the same result

[1024MAK]

With an iPad, up is with the volume buttons on the top...

Or you can use the picture editer to rotate the picture.

My brain is a bit fuzzy today (so my head has an head ache, so may be wrong here), but do your settings have "pin cushion" in the settings?

Mark

[Bryce]

That's not as simple as a pin-cushion problem, there's a definite "wave" in there. Did you mess with some refresh rate setting?

Bryce.

[Dr Tiger Ninestein]

1024MAK. Nope, not that I can see.


Bryce. No I don't think so. Here's a list of the settings in the service menu that I played around with.


      Red HWB
      B&W HWB
      Blue HWB
      Green HWB
      Ver size
      Ver breadth
      Pin ampl
      Par tilt
      V linear
      Corn corr
      Vcen Ew
      V position
      H centre
     
These are the only settings in there, but none of them seem to effect the wave at all. To be honest it's not that noticeable a lot of the time but on certain screens such as when using the super gameboy or when there are straight lines on either side of the screen its obviously really noticeable.

[Bryce]

Just a guess here, but I'd bet on it being a conbination of V Breadth and posibbly V Linear.

Bryce.

[Dr Tiger Ninestein]

Ok cheers Bryce. I'll have a play around with those two and see if it makes a difference.

[||C|-|E||]

I actually finished solving all the problems with the screen today! The solution was a combination of things that involved fully recapping the board of the monitor and re-adjusting the yoke, but now it looks basically like a new monitor, so I am very happy. I would like to thank Bryce for all the support, without him it would have been completely impossible to tackle this issue and, moreover, he was very patient with me these days that I was bombarding him with private messages (I am truly sorry  ). I took some pictures if somebody is interested to see them, although I guess that describing the whole process has only limited interest because it is quite dangerous.

[robcfg]

I think that because it's a dangerous procedure, better have it well documented.

[Gryzor]

I've been itching to mark this topic as Solved

[||C|-|E||]

I think that because it's a dangerous procedure, better have it well documented.

I can upload some pics and describe what I did then, just bear in mind that I am not an expert in the field at all and definitely not the most qualified person to explain how CRTs work or are repaired 

[Bryce]

I actually finished solving all the problems with the screen today! The solution was a combination of things that involved fully recapping the board of the monitor and re-adjusting the yoke, but now it looks basically like a new monitor, so I am very happy. I would like to thank Bryce for all the support, without him it would have been completely impossible to tackle this issue and, moreover, he was very patient with me these days that I was bombarding him with private messages (I am truly sorry  ). I took some pictures if somebody is interested to see them, although I guess that describing the whole process has only limited interest because it is quite dangerous.

I don't mind being bombarded with questions. It's a difficult and dangerous project, especially as a first major electronics project. I'd prefer to be answering lots of questions rather than asking the question "Why doesn't ||C|-|E|| log into the forum any more?"
Really glad that everything went so well.

Bryce.

[chinnyhill10]

I am not an expert in the field at all and definitely not the most qualified person to explain how CRTs work or are repaired 

I was told of a story yesterday where a Commodore monitor was making a buzzing crackling noise. When opened by a qualified engineer for inspection sparks were flying around the outside of the tube enclosure. The entire thing was a high voltage death trap and was scrapped.


CRT's are dangerous. Just because someone on here has been unwise enough to open theirs, doesn't mean anyone else should be encouraged


Just because you see someone going and playing in the middle of the road, doesn't mean you should. I fear documenting it will encourage idiots to try their hand at a risky procedure.


Lecture over.

[Bryce]

I was told of a story yesterday where a Commodore monitor was making a buzzing crackling noise. When opened by a qualified engineer for inspection sparks were flying around the outside of the tube enclosure. The entire thing was a high voltage death trap and was scrapped.

CRT's are dangerous. Just because someone on here has been unwise enough to open theirs, doesn't mean anyone else should be encouraged

Just because you see someone going and playing in the middle of the road, doesn't mean you should. I fear documenting it will encourage idiots to try their hand at a risky procedure.

Lecture over.

Very wise words. I would also not be in favour of documenting CRT repairs, for fear that my advice could be filling graveyards.

The story about the flying sparks is real and can actually happen quite often with monitors this old. It happens when the insulation of the HT lead to the CRT (that big red wire with the "suction cup" on the side of the tube) has become brittle and cracked. The high voltage will then jump out of the lead across to the nearest grounded metal (or you if you happen to put yourself in the wrong place). It looks spectacular, but it's extremely dangerous.

Bryce.