Atari SC1224

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qq1975b
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Atari SC1224

Post by qq1975b » Wed May 20, 2020 8:02 pm

Hi,

I have an Atari SC1224 where I cannot adjust the vertical size properly. It wasn't centered so I opened it and regulated R626 as said in the service manual. It reached its top but there is still a black zone on the top part. Is there any way to solve this? I mean, I would like the image to fill all the screen. When I play some demos that use overscan there is always this black zone on the top and I would like to be able to remove it. My SC1224 is a Goldstar one.

Thank you.
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derkom
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Re: Atari SC1224

Post by derkom » Wed May 20, 2020 9:32 pm

qq1975b wrote:
Wed May 20, 2020 8:02 pm
I have an Atari SC1224 where I cannot adjust the vertical size properly. It wasn't centered so I opened it and regulated R626 as said in the service manual. It reached its top but there is still a black zone on the top part. Is there any way to solve this? I mean, I would like the image to fill all the screen. When I play some demos that use overscan there is always this black zone on the top and I would like to be able to remove it. My SC1224 is a Goldstar one.
Vertical size is adjusted via R616, which you should be able to access at the back of the monitor, without opening the case.

Screenshot 2020-05-20 at 23.31.56.jpg
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qq1975b
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Re: Atari SC1224

Post by qq1975b » Thu May 21, 2020 7:34 am

Hi, thank you for the comment.
I know and I did it but then the screen grows on both sides: top and down. I can make the top to look ok but the down goes down the visual screen, so I lose part of what I should be seeing. And I can't make it more centered because the centering screen regulator it is at its top.

Or maybe the problem are the capacitors of the monitor?

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Re: Atari SC1224

Post by exxos » Thu May 21, 2020 9:27 am

I know nothing about those monitors, but sounds like you need a vertical location adjust not vertical size ?
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derkom
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Re: Atari SC1224

Post by derkom » Thu May 21, 2020 9:29 am

If you're unable to centre it with the centring control, then something is clearly out of spec. If the caps haven't been replaced, it's not a bad idea. I replaced all the electrolytic caps in my SC1435 last year and saw a nice improvement in clarity. (Didn't have any centring problems though.)

Looking over the service manual for the SC1224, it looks like all the "CE" caps are polarised, which is helpful. The 1435 has one NP cap whose exact replacement is stocked only by Console5 in the US, so that one was a bit expensive. Do pay attention as you look at the actual device to ensure that you're not accidentally replacing a NP cap with a polarised one, or you will get some extra, very brief excitement when you turn it on.

If you go this route, the assumption is that you know what you're doing and won't kill yourself. :) The unit *probably* has a bleed resistor in the flyback, but don't take my word for it. Safely discharge the tube before doing any work regardless.
exxos wrote:
Thu May 21, 2020 9:27 am
I know nothing about those monitors, but sounds like you need a vertical location adjust not vertical size ?
He adjusted that, and hit the end. That's what R626 is.

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Re: Atari SC1224

Post by exxos » Thu May 21, 2020 9:46 am

I've not looked at the schematic, but in old stuff there used to be a dedicated chip for generating the frame. I've seen corrosion on resistors and burnt resistors causing odd issues like that. Indeed caps also a factor.
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qq1975b
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Re: Atari SC1224

Post by qq1975b » Thu May 21, 2020 11:29 am

Here there is the service manual. I don't know if it would be good to replace other parts, besides the caps, related to the vertical centering.

https://docs.dev-docs.org/htm/search.php?find=_F

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Re: Atari SC1224

Post by derkom » Thu May 21, 2020 12:50 pm

qq1975b wrote:
Thu May 21, 2020 11:29 am
Here there is the service manual. I don't know if it would be good to replace other parts, besides the caps, related to the vertical centering.
As @exxos noted, there are a couple of ICs involved in building the picture as well, but since they're unique to these (and some similar) monitors, if it were me, I'd start with the electrolytic caps and see where I am after doing that. They're going to need replacement anyway, and they're all easily and inexpensively acquired from a good parts supplier.

Other parts that tend to go on these monitors are the flyback transformer and the horizontal deflection transistor, but your problem doesn't show any symptoms of those issues, so again I wouldn't bother with these. The deflection transistor (2SD1453) is actually a pretty simple and inexpensive replacement, and you might consider proactively replacing it sometime, but not now. No sense risking introducing more problems when trying to solve one problem.

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Steve
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Re: Atari SC1224

Post by Steve » Thu May 21, 2020 1:37 pm

Might be worth asking Sanford's advice also as he recently fully serviced his sc1224:

viewtopic.php?f=35&t=1529
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qq1975b
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Re: Atari SC1224

Post by qq1975b » Thu May 21, 2020 3:29 pm

Ok, I will do that.

By the way, these transistors are 2SD1453 compatible?

https://www.mouser.es/Semiconductors/Di ... u6Z1z0w0x4

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