Pixel positions offset differently by color channels.

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Mendel
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Pixel positions offset differently by color channels.

Postby Mendel » March 7th, 2017, 9:08 pm

I have this issue on my new astro city monitor that different color channels of same pixels on my monitor are placed such that not all color channels seem to land on same pixel positions. Worst is the blue color that seems to be offset by several pixels.

Let me be clear, its not just that the colors bleed out to neighbouring pixels, they actually seem to start at wrong position.

Image
(color bars on Street Fighter 2: ce test mode)



Note where the left edge of the blue color bars is. My theory is that the left edge of every color bar should be aligned. (seems to be like that on emulators at least)

This leads to partial blue ghost images particularly of small text and sprites and makes the image not so pleasant to watch.

Is there anything that could be done about such an issue?

I can seem to decrease the effect a little by adjusting the blue gain pot under the control panel, well at least it reduces the bleeding... but then there is clearly wrong color balance (not enough blue).
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 7th, 2017, 9:43 pm

it's convergence. If the middle of the screen is affected, it's static convergence (adjusted by convergence rings on the back of the tube). If it's the corners and/or edges, it's dynamic convergence. Dynamic is most easily adjusted by adding convergence strips on the back of the tube.

That's the high-level explanation. I suggest researching and learning about all of these things then determining how to best solve the issue, in practice. :penser:
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Re: Pixel positions offset differently by color channels.

Postby grantspain » March 8th, 2017, 12:03 am

to prove it is convergence you could do with displaying a grid pattern
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 3:42 am

Well, here goes

Image

I think it is both on corners and middle of the screen... maybe ever so slightly worse towards the edges of the screen.
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 8th, 2017, 4:24 am

Definitely convergence. Start with static. Check out some youtube videos on adjusting static convergence, and what each set of rings does. Static convergence alone may get you to a much better place that you are happy with. Some warnings - adjusting convergence is done with the cab on. The monitor has high voltage. There should be some good warnings in any video you watch - heed them. Adjustment can be done safely with necessary precautions taken. Warning 2 - it can be a tedious process, so come with lots of patience. Recommendation 1 - mark the starting position of the rings before making any adjustments. Take a sharpie and draw a straight line across all the rings. That way if things go sideways (not literally), you can start over. Recommendation 2 - setup a mirror in front of the cab so you can more easily adjust and see what you're doing without leaning around the edge of the cab. Most importantly this allows you to focus on working safely.

Good luck with it!
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 7:40 am

I cant see any such rings that I should adjust.

I am scared. Im not even sure it is safe to touch that metal thing.

Image

What do you reckon would happen if I took those middle two screws off? Is it just a safety block or is it actually attached to and holding something important on the other side?

Yeah the convergence is pretty bad but I bet dying would be worse still.
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 8th, 2017, 7:44 am

Mendel wrote:I cant see any such rings that I should adjust.

I am scared. Im not even sure it is safe to touch that metal thing.

Image

What do you reckon would happen if I took those middle two screws off? Is it just a safety block or is it actually attached to and holding something important on the other side?

Yeah the convergence is pretty bad but I bet dying would be worse still.

:lol: yeah you're right. It's sppears protective only but I would defer to someone who's more familiar with those cabs on how to safely remove. Probably just wear some rubber gloves while removing, then you will have access to discharge the tube safely and proceed. But again, hoping someone more knowledgeable will chime in.
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 7:57 am

ummhh... discharging the tube doesnt sound like something plausible if the adjusting is supposed to be done while the monitor is on :)

I think I will give a call to some local electronics maintenance service to see if they still have people who are at least familiar with crts of any kind.

Any recommendation on other games that have a nice color pattern/test screen to help with adjustment if and when I get some help to do it? (I could fire up mame to use a rom of some game or the other to help with adjusting.)
Last edited by Mendel on March 8th, 2017, 8:49 am, edited 2 times in total.
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Re: Pixel positions offset differently by color channels.

Postby crunchywasp » March 8th, 2017, 8:14 am

That metal thing's just a shield/cover and is easy to remove without disturbing anything - it's not attached to the tube or chassis.

If you do decide to remove it, do it with the power off in case it makes contact with anything when you're taking it off. I find the easiest way to remove it is to take out the 2 screws that fix the cover to the bar, leave the cover to support itself where it is, then take out the screws that hold the bar on the monitor frame, take out the bar while holding the cover, then free the cover. You'll be able to get to the back of the tube and the chassis then.
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 8:44 am

well, I decided to give it a shot and seems like the screws in the middle have rusted in or something as they are in place VERY firmly. I even put some weight on it and pushed the screws and tried to turn them but all I managed to do was to slightly erode the end bits of the screws. crap. The two screws on the sides seem to turn easily.

edit: but I was able to remove the screws on the sides and with a bit of fiddling around the cover came off while still attached to the bar. I feel like it scratched something on the way off though. I hope I didnt break anything...
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 8:58 am

I think I can see the target between the tube and some pcb now

Image
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 10:01 am

So based on a youtube video I thought the middle ring would be for red and blue convergence adjusting.

So I was supposed to be able to turn the things both together and separately to fine tune (theres two plastic bits on each ring). So I suppose on the middle ring one of those plastic bits is for red and one was for blue.

My method of adjusting was to have one hand behind my back and another hand with a rubber glove holding a thin screwdriver with plastic end bit on my hand and sharp metal bit towards the adjustment rings.

First problem was, I was unable to turn the blue without the red following it, they seemed a bit stuck.

So, I thought I would sort of place the screwdriver between the plastic bits and turn it a little to detach the plastic bits from each other, so I could follow with tuning the red and the blue individually.

Result is such a simple and utter failure.

Image


Well, I didnt get electrocuted but the picture isn´t any better either. Now I suppose this will be impossible to adjust going forward.
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 8th, 2017, 3:01 pm

Mendel wrote:ummhh... discharging the tube doesnt sound like something plausible if the adjusting is supposed to be done while the monitor is on

Yeah you're right. Not applicable here, sorry about that. :oops:

Anyway, I assume that's one of the ring tabs? Not the end of the world but as youve found, they can sometimes get brittle with age and are meant to only travel in a linear direction (not to be twisted or bent).

You can use anything non conductive that gives you enough leverage to move what's left of the ring but obviously exercise caution so there's no further damage. Also, if you move the other good ring of that pair, it should move both together.

There are plastic crt/tv adjustment tools that you can get. A fellow by the name of Bob Roberts used to sell them here in the states but he has recently had health issues and is no longer in the business. The local big box electronics store also has them. Don't know what you've got near you, but might be worth looking for a set. Especially if ever needing to adjust horizontal width. That cannot be adjusted without the correct plastic tool.

But, back to the main subject. Unless the damaged ring is completely broken through and wont turn and only gets worse when you try to adjust, then you should be able to keep going at it. And sgain, it can be tedious. Lots of trial and error. I've had good success on the 2 monitors that I spent about 30 mins each, adjusting static convergence. Not a perfect result on either, but much better than before adjusting.
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Re: Pixel positions offset differently by color channels.

Postby nem » March 8th, 2017, 3:58 pm

Trying to adjust the rings from the NAC back door will end in disaster.

Pull out the monitor.

With an x-acto knife separate the rings from each other.

Pull all the monitor wiring out from the PCB door, try to get as much length on them as possible.

Connect monitor outside the cab.

Spend 10 minutes to get convergence looking nice. Spend the next two hours trying to get it perfect.

Also, there aren't separate rings for colors, it doesn't work that way. Technically, the second two rings should adjust vertical lines, and the third set horizontal, but honestly, I don't think it works quite that way either.

EDIT: oops, corrected a mistake
Last edited by nem on March 8th, 2017, 5:30 pm, edited 1 time in total.
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 8th, 2017, 5:27 pm

nem wrote:Spend 10 minutes to get convergence looking nice. Spend the next two hours trying to get it perfect.

:lol: exactly

The rings are:

1st set - purity - closest to tube
2nd set - red/blue - middle set
3rd set - red/blue relative to green - closest to neck board

Sometimes, however, these are reversed - purity is closest to neck board and red/blue is closest to tube.

Purity can probably be ignored. If you have the ability to generate a white screen, you can check for any coloration/discoloration anywhere within the white. If you find it, then turn down the blue and green pots, so you have only red showing. Adjust purity to get a uniform red.

For the other two, use a cross hatch pattern.

For red/blue - separating the rings will move the beams horizontally (side to side), so
for that adjustment, you must look at the vertical lines of the crosshatch
to see the effect. Holding and moving both rings together moves the beams
vertically. To see that effect, you need to watch the horizontal lines at
the center of the screen.

For red/blue relative to green -this set sets the convergence of MAGENTA (RED+BLUE) AND
GREEN. AS before, Looking at the center of the screen, separating the rings
allows for horizontal beam movement (observe vertical lines) and rotating
both rings together moves the beams vertically (observe horizontal lines).
All slot-mask picture tubes use a variation of this setup procedure.

Some good informational sources, which you may have already found. A bit of reading, but good to understand the concepts while attacking it:
https://www.repairfaq.org/samnew/tvfaq/tvcrtcona.htm

http://www.arcaderepairtips.com/2010/08 ... nce-rings/

http://personalpages.tds.net/~rcarlsen/ ... nverge.txt
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 8th, 2017, 8:58 pm

NoAffinity wrote:You can use anything non conductive that gives you enough leverage to move what's left of the ring but obviously exercise caution so there's no further damage. Also, if you move the other good ring of that pair, it should move both together.


Moving them together is possible, yes. but trying to keep one half of the "ring-pair" in place" while moving the other half now seems impossible at least with the backdoor method and using screwdriver and one hand only.
I am not going to use two hands cause then I would have a chance of being part of an electric diagram, which Im not looking forward to. Also to add to the challenge my hands have a tendency to shake...

The bit where I pull out the monitor is also something Im not confident in doing. The scenario where I do this myself is over. I gave up.

I might still try to call someone to come help with it though.

Thank you all for your help and tips though, much appreciated!
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 8th, 2017, 9:11 pm

Sorry it didn't go well, mate. Unfortunately in this hobby, there are often "unforeseens". Hopefully someone local can help you out and get it dialed in.
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Re: Pixel positions offset differently by color channels.

Postby Mendel » March 10th, 2017, 10:21 am

So I found a local electronics repair companyt that has been there for a while and they have a guy who is basically oldskool crt tv repairman.

He would likely be able to help.

However, in preparation for that, I would prefer to have some kind of better test screen pattern. Do you know of any game that has a good test screen, (better than white crosshatch or the color things in sf2)

I suppose a test screen like in this video could be ideal: https://www.youtube.com/watch?v=nxOvYVcN1fc&t=305s

But do you happen to know if that is from some game test screen or something else entirely?
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Re: Pixel positions offset differently by color channels.

Postby NoAffinity » March 10th, 2017, 6:26 pm

All of the NBA Jam and Mortal Kombat -era Midway games have a good test menu with multiple screens. You can look at any of the PCB game manuals to see what the list of available screens are.

What is shown in that video is craftymech's Test Pattern Generator. It's a pretty awesome tool. I've got one, and have cables for the standard monitors you find in American cabs (Ninentdo, WG, Hantarex). However, I looked at the Nanao in my Aero City, and I think it is unique from those. Going to try to check the Nintendo cable, and see if it will fit, this weekend.

But, without taking that too far into the weeds, the 90's midway boards have good screens if that's something you can get your hands on. Heck, if all you want it for is the test screens, see if you can find a Super High Impact board. There is zero demand for that game, they sell cheap. You don't even need the cables, daughter board(s) or anything else, just the main board.

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