vertical lines on many XE computers

[flashjazzcat]

Haven't really been able to improve the 130XE picture any further. I'll be able to finish it if anyone can suggest the causes of this effect:

 

 

I may be a perfectionist, but the vertical geometric distortion depending on the luminance of adjacent pixels isn't present on the 800XL.

[flashjazzcat]

It occurs to me that the diode is a kludge: Ironically, the 800XL chroma signal is perfect for a modern TV at source. I may try higher resistor values on the XE.

[flashjazzcat]

Found some interesting reading here about the peculiarities of the XE video circuit. The XE only uses one transistor on the colour circuit, and leaves it the the RF modulator to cancel out the "DC offset" which the XL has a dedicated transistor for. I was wondering if this DC offset might be causing the problems with the vertical lines/grain/noise from a stock 130XE. I tried adding a transistor in front of L5 in the circuit (instead of the diode at R205). Effects were appreciable but imperfect. Signal was very clean, but colour fields tended to bleed in the black margin area of the screen (vertical blue lines above and below the playfield, and a thick purple stripe down the right hand side). The blue GR.0 screen was in itself quite acceptable. I'm at a loss as to a way to further modify the signal to get rid of the interference.

[Rybags]

Build your own seperate video circuit which uses it's own power supply? ie - it's own wall-wart, so you get a minimum of electrical interference coming from other parts of the machine.

[flashjazzcat]

Build your own seperate video circuit which uses it's own power supply? ie - it's own wall-wart, so you get a minimum of electrical interference coming from other parts of the machine.

That would be the ideal solution. A self-contained unit - basically a copy of the 800XL circuit which could be hooked up to GTIA at one end and the s-video pins at the other. I know people have divergent experiences of the various Atari models, but for my money the 800XL circuit appears superior to the XE's simplified circuit. Once the luma and chroma are isolated on the XL, the picture looks stunning. Not so with the XE. Of course, all TVs are going to give different results. I just love the fact that the XL needs to diodes to cancel out crap. I've been able to mix and match parts of the Supervideo mod, with the knowledge that all it's doing is refining the picture: none of the components have to deal with noise or grain.

[Jacques]

flashjazzcat: your modifications of 800XL (not XLF) look very promising. I'm dealing with some problems on 800XL S-video, too - basically with some artifacting in the chroma channel (LUMA is crystal clear after disconnecting R54 and R56).

1. Could You please let me know which place exactly You have taken the CHROMA signal from to put into monitor port's PIN5?

2. And beside from removal of the block of resistors/condensators (your photo) have you changed sth regarding LUMA signal which is by default connected to monitor port's PIN1?

3. Do You really have no colourful artifacts in HIRES B/W screen, like in the Sysinfo screen, because I'm still having them, even though LUMA itself is crystal clear and CHROMA is taken almost directly from the GTIA's COLOR signal (only through resistor and condensator added by me).

 

Your explanation on the above points would be great appreciated, hopefully I can have it sorted out on 800XL, too!

[dmlloyd]

The color signal is AC at (nominally) 3.58MHz or so. So you can use a capacitor (e.g. 10uF should be more than enough) with the "-" side pointing at the s-video jack to isolate the chroma signal if you think it's a problem. Most monitors will do their own isolation though, from what I've seen anyway.

 

To Jacques: I don't think that the GTIA's chroma output has enough "juice" to fully drive the chroma signal. You need, at a minimum, some simple amplifier circuit, like this one: http://www.retrocomputing.net/parts/atari/130xe/docs/sv130-20.gif (this is for the XE, not the XL, and mainly for illustration; the chroma amplifier is the bottom right-hand circuit starting at R201. You can leave off L6 if you want as well.)

 

If you have colorful artifacts in hires modes, this means that the luma circuit is affecting the chroma circuit in some way, period. Possible causes can be AC noise between the amplifier circuits (notice in the above link the 10uF capacitor below R116 - this will eliminate much of the noise going into and out of the luma circuit; also notice the large 220uF capacitor which provides AC bypass for the whole video circuit, another noise-reducing measure). Or there might be an interconnect for the composite video that you missed somewhere.

[Jacques]

Thanks dmlloyd But that's why I need to know the rest of flashjazzcat's mod apart from removing those elements, especially the places which he's taken LUMA and CHROMA afterwards.

 

P.S.

And yes, GTIA's COLOR signal has enough "juice" to fully drive the chroma signal, just used 2K resistor and 1uF condensator on the way out, as advised here by Jer (Jerzy Sobola): http://atariarea.krap.pl/forum/viewtopic.php?id=7419 However while the LUMA is crystal clear when I remove CHROMA signal from monitor PIN5, then when both are connected (PIN 1 LUMA, PIN5 CHROMA) I'm getting artifacts on HIRES B/W screen. That's why I need exact clarification on flashjazzcat's modification for 800XL to do just about the same (if he's not having any artifacts).

Edited January 4, 2010 by Jacques

[flashjazzcat]

Sorry - been re-wiring my SIO2SD/XM301 tonight (still can't get the blasted power LED to light). Wife says time's up on the computer tonight () so I promise I'll take the lid off the 800XL in the morning, take pics, and do a quick write up. I really need to inspect it myself to explain it properly. However - the main thing about it is that both the RF box and ALL components forming a join between luma and chroma have been disconnected. Those two steps alone transformed the picture - believe me. The rest is just finessing... proper write up tomorrow. Hope that's OK.

Edited January 4, 2010 by flashjazzcat

[Jacques]

Sure, thanks! Waiting patiently...

[flashjazzcat]

Here you go - top item on the projects page. Direct link here. I call it "UltraVideo"! Edited January 5, 2010 by flashjazzcat

[Jacques]

Thank you very much flashjazzcat!

 

Two final questions:

 

1) could You please let me know where do you exactly take the CHROMA signal from after this mod, which is later connected to monitor connector's PIN 5 (CHROMA is not connected in there on older XLs)?

2) Do You really have no artifacts on HIRES B/W screen, like the Sysinfo program?

[Ransom]

Thank you for sharing your findings, Jon!

[flashjazzcat]

Thank you very much flashjazzcat!

 

Two final questions:

 

1) could You please let me know where do you exactly take the CHROMA signal from after this mod, which is later connected to monitor connector's PIN 5 (CHROMA is not connected in there on older XLs)?

2) Do You really have no artifacts on HIRES B/W screen, like the Sysinfo program?

 

1) My apologies: I should have covered that in the guide. You need a 100ohm resistor (brown-black-brown-gold) attached to the junction of R67 and R68. Hook up a wire between the resistor and the chroma pin. It's normal practice to do this on the underside of the board. It's explained in step 8 of the original SuperVideo guide here. I'll update my guide to include it.

 

2) Artifacts are absolutely banished by this mod. See here:

 

[Jacques]

Great! And again, thank You very much! I just needed the confirmation for the CHROMA source as I tried several things (including original Supervideo mod and also taking CHROMA from GTIA directly) by myself in order to get perfect s-video signal from my 800XL. Now I'll follow your footsteps on this subject

Edited January 5, 2010 by Jacques

[Jacques]

Hi again, and especially flashjazzcat, as the s-video output quality is after this mod is still not satisfying in my 800XL, so hopefully someone could help - it would be greatly appreciated

 

I've done on my 800XL (+1MB RAM, QMEG 4.04, stereo) the following things concerning s-video/ultra mod:

 

1) disconnected RF modulator

2) removed elements R56 up to R68

3) R53 and R66 replaced with 75 Ohm resistors

4) R116 value is now 10 Ohm (shouldn't matter)

5) taken the CHROMA signal from the R67 & R68 junction through a 100 Ohm resistor and leaded into monitor's PIN5.

 

SO now, my video circuit is looking like this:

 

 

 

However the quality of the S-VIDEO picture is still mess, I have vertical bars and plenty of colourful artifacts, visible mainly on the white graphics.

Can anyone help to find a reason? Please take a look at the below screenshots:

 

 

 

HEEEEELP!

 

P.S. The strange thing is, that if I take CHROMA directly from GTIA's COLOR signal through the 1uF capacitor and 2K resistor, I'm getting much better video than above (almost no bars, but still some artifacting, but much less). But I'd like to get it to work the way it's working for flashjazzcat.

[Jacques]

Hi again, and especially flashjazzcat, as my s-video output quality after I made this mod is still not satisfying in my 800XL, so hopefully someone could help - it would be greatly appreciated

 

I've done on my 800XL (+1MB RAM, QMEG 4.04, stereo) the following things concerning s-video/ultra mod:

 

1) disconnected RF modulator

2) removed elements R56 up to R68

3) R53 and R66 replaced with 75 Ohm resistors

4) R116 value is now 10 Ohm (shouldn't matter)

5) taken the CHROMA signal from the R67 & R68 junction through a 100 Ohm resistor and leaded into monitor's PIN5.

 

So now, my video circuit is looking like this:

 

 

However the quality of the S-VIDEO picture is still mess, I have vertical bars and plenty of colourful artifacts, visible mainly on the white graphics.

Can anyone help to find a reason? Please take a look at the below screenshots:

 

 

 

 

HEEEEELP!

 

P.S. The strange thing is, that if I take CHROMA directly from GTIA's COLOR signal through the 1uF capacitor and 2K resistor, I'm getting much better video than above (almost no bars, but still some artifacting, but much less). But I'd like to get it to work the way it's working for flashjazzcat.

Edited January 6, 2010 by Jacques

[flashjazzcat]

What kind of cable are you using? If it has a diode in it, chances are it's the cause of the artifacting. It certainly was in my case.

[Jacques]

It's almost clean S-video cable. It only has a diode put by me on the CHROMA line. But I already tried with the diode removed (the diode is used to get rid of zig-zag effect on the unmodified 130XE s-video connection) and the artifacting did still occur for 800XL. The strange thing is also that with CHROMA taken from GTIA directly (thorugh capacitor + resistor as mentioned above) instead of R67+R68, there's almost no vertical banding and the artifacting is smaller. Hmmm... My mainboard is 800XL (not XLF) rev. D. There must be still sth wrong in the video circuit...

[Rybags]

Try running on Luma only - disconnect chroma on your cable temporarily. At least that might help work out what's causing the problem.

[Jacques]

With CHROMA disconnected the LUMA is almost perfect - no artifacts, no vertical bars.

[flashjazzcat]

With CHROMA disconnected the LUMA is almost perfect - no artifacts, no vertical bars.

That's a good place to begin. I'm totally puzzled as to why you're getting artifacts. There should be no link remaining between the two circuits. Maybe the mod as I did it isn't optimal for your CRT monitor with regard to vertical bars.

[Jacques]

I'm using 17" Samsung LCD-TV monitor and it's s-video connector. And with this, both vertical bars and so intensive artifacts appear. While from unmodified 130XE's s-video there are no colorful artifacts at all using the same cable and monitor.

 

Please also note that if I take the CHROMA (COLOR) signal from GTIA's directly (details in one of my very previous posts) the vertical bars are almost unnoticable and there's less artifacting (but still present).

Edited January 7, 2010 by Jacques

[Rybags]

Just because a monitor or capture device has S-Video input, doesn't necessarily mean it gets processed as such.

 

Every chance the signal is recombined and processed the same as composite.

[Jacques]

Just because a monitor or capture device has S-Video input, doesn't necessarily mean it gets processed as such.

 

Every chance the signal is recombined and processed the same as composite.

 

It IS processed as S-VIDEO. There's no artifacting from 130XE's S-video, period. Plus the vertical bars also indicate there is a problem. And the problem IS on that XL, not anywhere else I also indicated several times that the problem is on the video circuit as it looks worse when CHROMA is taken from R67&R68 junction (after the mod) than from the GTIA's COLOR signal directly. So no cable and no monitor is the reason. Somehow there's still a problem in my 800XL with this mod, so just believe me and please let's focus on video circuit, as I excluded all potential external reasons of the problem.

 

Strange, btw...

Edited January 7, 2010 by Jacques