Author Topic: Adjusting the image in the original screen.  (Read 5120 times)

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Offline ||C|-|E||

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Adjusting the image in the original screen.
« on: 15:02, 17 March 16 »
Hello!
I know that lately I am bothering you a bit too much with all my hardware "problems", sorry, this is what happens when you buy stuff from e-bay from time to time  :picard2: Luckily, I did not experience any serious issues, just minor things that needed to be adjusted.

Now is time for the screen. I received it a few days ago along with a working 464 Plus and I am actually very happy with it. I was carefully cleaning the unit and it works very well. Sound is good, color is bright and image is crisp. However, there is a BUT, and in this case is the geometry of the image. It turns out that the image is apparently slightly rotated counterclockwise. However, if you check more carefully, the "rotation" mostly affects the top right corner. So, some of the electrons are actually traveling a bit longer than they should. I have a big speaker next to the screen, and the first thing I tried was to remove it, but it did not help. Now I remember that I also have a subwoofer below table that I did not touch, I will try this today. But, in any case, assuming that it is the screen itself, could you tell me if there is a proper way to adjust the geometry a little bit? or, in case I need to check something in particular inside could you point me to it? I have quite a lot of experience with audio amplifiers, but not with CRTs, I never liked to mess with them so much for obvious reasons  :D

This morning I took a picture for you to see. If you check carefully, the image is a bit bent toward the upper right corner (sorry for all the stuff that appears around)

[attachimg=1]

Any help be much appreciated!!



« Last Edit: 15:24, 17 March 16 by ||C|-|E|| »

Offline Grim

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Re: Adjusting the image in the original screen.
« Reply #1 on: 16:02, 17 March 16 »
I'm not sure if there is anything in the monitor to adjust that (I think not, but if there is, there's a good change it should be indicated in the service manual). While cleaning it up, did you moved somehow the internal speakers? But from the picture, I think it is Prophet's nanosuit trying to absorb the electron beam :)

Offline ||C|-|E||

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Re: Adjusting the image in the original screen.
« Reply #2 on: 16:21, 17 March 16 »
Hahahaha, no, I did not move the magnets. Maybe it is actually Prophet, who knows! Checking the service manual of the other models of Amstrad screens I found that there are some knobs inside that could be probably used, but I never tried to adjust anything like that. That is why I am curious to see is somebody did it in before  :)

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #3 on: 16:44, 17 March 16 »
A little "rule of thumb" I learnt back when I was fixing TVs regularly: Only symetrical problems (such as pin-cushioning) can be fixed with adjustments, if it's non-symetrical it's usually some component that's failing or has failed.
In your case it could be a convergence problem (colours not lining up properly) or there's a similar issue where the top left border gets slightly dragged to the left (there's a name for this, which I can't remember at the moment). Both of these issues can be due to several things, but in a device this old, my first bet would be capacitors dried out and dying.

If you can display a squared grid on the screen and post a picture of that, it would be easier to analyse the problem.

Bryce.

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Re: Adjusting the image in the original screen.
« Reply #4 on: 16:52, 17 March 16 »
Thank you Bryce! I will display the square grid then  :) Replacing the capacitors should not be more difficult than usual if this is necessary. I will just try not to end like a fried chicken  :picard: . One thing I noticed is that there is not convergence problem as such, all the colors are displayed very properly (at least judging by eye), is just the slight deformation.
« Last Edit: 16:53, 17 March 16 by ||C|-|E|| »

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #5 on: 17:27, 17 March 16 »
It's difficult to tell from the picture you posted, but I think the whole picture is equally rotated. If this is the case, then it's just an adjustment. However, the point of adjustment is very near the scary voltages, so you need to be careful if you do this. The process is even described in the CM14 service manual.

Bryce.

Offline ||C|-|E||

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Re: Adjusting the image in the original screen.
« Reply #6 on: 17:49, 17 March 16 »
The picture is a bit rotated as a whole, yes. I will display a grid tonight and then we can check if, besides the general rotation there is something else. I am a bit scare to do the adjustment but oh well...

Offline ZbyniuR

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Re: Adjusting the image in the original screen.
« Reply #7 on: 23:59, 17 March 16 »
Don't be pussy, just open it and try tuning every yellow screw till you find right and make it perfect.
You will be proud of yourself.
Big mirror will be helpfull. :)
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Offline 1024MAK

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Re: Adjusting the image in the original screen.
« Reply #8 on: 01:01, 18 March 16 »
From the picture you posted, it looks like the defection yoke has moved slightly. It is held in position with the aid of three wedges. See section 3-4 Dynamic Convergence on page 44 of the service manual (Service Manual Amstrad Plus).

Mark
Looking forward to summer in Somerset :-)

Offline ||C|-|E||

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Re: Adjusting the image in the original screen.
« Reply #9 on: 02:29, 18 March 16 »
I made a little set of tests to better diagnose the problem, but I think that the most informative one is this grid.

[attachimg=1]

It really seems that is a problem of general rotation, yes. I also prepared some more texts that display color bars and the convergence is, at least by eye, perfect. This screen is super-bright too, I have to keep the brightness at around 75%, otherwise is just too much for me  :)

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #10 on: 14:19, 18 March 16 »
Don't be pussy, just open it and try tuning every yellow screw till you find right and make it perfect.
You will be proud of yourself.
Big mirror will be helpfull. :)

The rotation isn't done by any of those "yellow screws" you speak of. Re-aligning the rotation involves loosening the deflection coil and turning it slightly (as 1024MAK mentioned). The screen with grid looks like your main problem is just rotation. It's relatively easy to do, but be extremely careful when doing anything inside a CRT that's turned on!
There may be a tiny bit of barrel distortion too, but that might just be the curve of the screen.

Bryce.

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Re: Adjusting the image in the original screen.
« Reply #11 on: 14:41, 18 March 16 »
Thank you Bryce!

I do not know if I will adjust it or live it the slight rotation. I mean, I know that it is not that difficult in theory but on the other hand I do not like the idea of messing with it at all, particularly when it is on. Although I have the manual I lack a step by step tutorial and I am not familiar with CRT screens.  On the bright side, I think that the barrel thingy I is just the curvature of the screen, nothing to worry about. I am sure that if I managed to find one of those technicians that used to repair TVs at home in the past it would be very easy for him to solve this.

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #12 on: 15:36, 18 March 16 »
I can understand your apprehension. Here's a step by step of what needs to be done anyway. This picture isn't from a CM14, but similar enough that everything will look pretty identical if you open your CM14.
So... We're looking at the rear end of a CRT. The green connector to the left will have a small PCB connected to it, kind of floating in the air, probably with 6 or 8 wires coming from it. Don't touch this PCB, it probably won't kill you, but it will hurt like hell. The deflection coil is the big copper windings you can see in the middle of the red circle. They are mounted on that big piece of white plastic. So what do you need to do? This coil (and it's plastic mounting) has rotated very slightly, which is why your picture has also rotated. It's held in place with rubber wedges at the screen end and usually just a single screw / pipe-clamp at the other end. Firstly, it may already be loose, so gently check whether you can rotate it back to the correct position before doing anything. If it doesn't move, you'll need to slightly loosen the screw I've circled in purple and then adjust it as required. When you're happy with the rotation of the picture, you just need to tighten the screw again. Be careful not to misalign the coil again when tightening the screw. DON'T TIGHTEN THE SCREW TOO MUCH OR THE TUBE WILL CRACK!!! Just enough to hold the coil in place. If you use a pair of insulated gloves (even kitchen "washing-up gloves" are enough) you can pretty much touch anything in that area. The only really scary bit that you need to avoid is a big red wire that goes to what looks like a plunger on the back of the screen. Don't go near this, even with the gloves. That's the HT line and carries several thousand volts, even when the TV is turned off and unplugged!

Bryce.

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Re: Adjusting the image in the original screen.
« Reply #13 on: 15:47, 18 March 16 »
Thank you so much, Bryce! Well, with this tutorial I think that I will be able to give it a try!  :D I understand that I do all the adjustments with the screen disconnected and then I check turning it on if everything is OK right? That way, if something goes wrong, "only" the capacitors will discharge  :-X . We should have proper gloves for this in the lab, we do not use CRTs but I am constantly working with electrophoresis chambers and I run my gels at 200V and 1A most of the time. Since this is enough to give you quite a shock and our chambers are physically open (with the liquid easily splashing when you move them) we have special disposable gloves. I will take a few with me today  :)

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #14 on: 15:56, 18 March 16 »
As long as the gloves are insulated and thick enough that a sharp point can't pierce them you are fine.

Regarding when to power it. I would recommend the following order: With the monitor turned off, open it up and position it where you can easily move around it and have good access to the areas of the tube you need. Check whether the coil moves, if not loosen the screw. Now power up the monitor and adjust the coil to the correct position (with gloves on). Tighten the screw again and unplug the monitor. Now you can close the case again and enjoy a straightened picture :)

200V (DC I presume) 1A - This is enough to send you to the fairies!

Bryce.

Edit: You may find that there are two screws on the neck of the tube. If so, you only need to loosen the one closest to the coil, the other screw shouldn't be touched.
 

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Re: Adjusting the image in the original screen.
« Reply #15 on: 16:13, 18 March 16 »
Thank you Bryce!! So, yes, our power supplies deliver those 200V and 1A when we are working with them in a ordinary way. I some cases, with huge chambers, I have set them to 400V and 2.5 A. We need to do this in a cold room, of course, otherwise the chambers tend to melt.  BTW, the wires that conduct the electricity in the chambers are made of platinum and I recently scrapped one. If you need some extra high quality conductive wire, I have a some here. It is crazily good, we use these wires immersed in solutions with high salt concentration and they never ever get rusty  :D

About the screen, I will open it and put it back in the little plastic stand I use. It seems very appropriate because I have plenty of space around to maneuver  :)

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #16 on: 16:20, 18 March 16 »
Let us know how it goes.

Bryce.

Offline khaz

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Re: Adjusting the image in the original screen.
« Reply #17 on: 19:18, 18 March 16 »
Some scary stuff in this thread. I have a couple of CRT I need to adjust by opening them, but I'm deathly afraid of doing so.
I'm considering buying these gloves Insulated 12kv High Voltage Electrical Insulating Gloves For Electricians HK |, but I'm not sure I'd be even able to move my fingers in them!



Related to the topic: the 240p test suite is a great set of tools to fine tune a CRT and measure metrics like display / input lag, etc. 240p test suite - XRGB wiki. You need one of the supported consoles (so many, the Wii being the best due to 240p/480i/480p support), but it's open source so maybe it can be ported to the CPC too?

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Re: Adjusting the image in the original screen.
« Reply #18 on: 19:33, 18 March 16 »
Let us know how it goes.

Bryce.

Sure, I will keep you all up to date  :) . One question, what´s the best part to grab and rotate? The white plastic? The black area between the copper coils? I guess that the white plastic, close to the rubber, is the best option, but just in case  :)

About the tests, the static ones are easy to port to the CPC, or they should be. In my case I just followed a dirty approach: using the visualizer I modified to check the graphics of our adventure I prepared some graphs in the PC and I converted them to SCR format. This works reasonably well.

Offline Bryce

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Re: Adjusting the image in the original screen.
« Reply #19 on: 22:58, 18 March 16 »
The way I do it: Don't loosen the screw much, so that it's still relatively difficult to turn the coil. Then set a screwdriver on one of the plastic ridges (there's usually several) and gently tap the top of the screwdriver with another screwdriver. It's much easier to fine tune it this way.

Bryce.

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Re: Adjusting the image in the original screen.
« Reply #20 on: 21:32, 19 March 16 »
Thank you!

I am at it right now! It is not extremely difficult, indeed, but tedious. It is easy to rotate it too little or too much and it tends to go back to the original position  :) However, the adjustment works! I hope to have it finished later today!  :)

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Re: Adjusting the image in the original screen.
« Reply #21 on: 22:31, 19 March 16 »
Of course, now I moved the magnets adjusting the other thing... very nice to make all the colors converge again, Jesus  :picard2:

I found that the technician that did the adjustment 30 years ago, or so, marked all the correct positions at that time, Good bless that guy, everything is back to the correct place  :-\ The pics I took helped as well  :-X

Edit: Now I also found that I had not moved the magnets, it was, of course, the iron of the screwdriver when close to the electron beam causing the problem and magnetizing the screen  :picard:

 
« Last Edit: 01:29, 20 March 16 by ||C|-|E|| »

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Re: Adjusting the image in the original screen.
« Reply #22 on: 23:46, 19 March 16 »
OK, the image is straight now :) The only problem is that, because of me coming and going with the screwdriver now the top right corner is magnetized and I see a with of a yellow staining in that region. Maybe I will have to degauss the screen, although it should go away over time, right?

Edit again: I demagnetized it with a small magnet, it worked wonders  :D
« Last Edit: 01:28, 20 March 16 by ||C|-|E|| »

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Re: Adjusting the image in the original screen.
« Reply #23 on: 03:47, 20 March 16 »
Adjusting the V-size now... that was completely wrong as well  :-X

Offline seanb

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Re: Adjusting the image in the original screen.
« Reply #24 on: 04:08, 20 March 16 »
Keep at it.
You'll get there one day.

Never give up.
Thou shall not question Captain Wrong!