SOLVED: Vertical Banding, Atari 800XL (<=RevC) @ sVideo.

[BillC]

I noticed that there was still a second composite connection at c175; wonder if this neede to be disconnected too.

C174/C175/C176 all connect to ground, so this shouldn't be a source of any feedback unless the ground connection is bad.

[+bob1200xl]

I would guess that you have some sort of cable/monitor problem. 800s, in general, have really good video. Somewhere in the monitor/TV or the cable the color signal is leaking into the luminance.

 

What kind of cable do you have? Are all the plugs separate? (meter them...)

 

Plug the LUMA cord into the COMPOSITE jack. Any color at all? Better not be.

 

What kind of monitor/TV do you have? If you plug in a s-video plug, does it disconnect COMPOSITE?

 

 

The 'bands' are just the color signal showing up on the LUMA signal. In COMPOSITE mode, the TV filters them out, which limits the video resolution to less than 3.5mhz. In s-video mode, there is no need for a filter (since there is no color signal on the LUMA signal), which gives you a much better resolution.

 

It's not the 800...

 

Bob

[crash]

The exact same banding is seen with the 800, 130XE, and 7800 (8-bit domain s-video board). The 7800 uses just an s-video cable, while the computers have a monitor to s-video cable, composite, audio cable. The same thing occurs on both of my televisions. I constructed the cable many years ago, and the lines are separate; I ordered a new cable that I can test soon, but I doubt this will resolve the problem due to the 7800. I didn't have this problem with older televisions/monitors, but it occurs on an LCD and plasma tv. I will have to try some of the things you suggest when I get home. If there is color on the Luma line, what do I do?

 

I'm happy to disable the composite video and RF modulators on all of these, because I will never use them again.

 

Thanks!

[+bob1200xl]

Analyze what you are saying: it worked on older displays - it does not work (has bands) on many different Atari sources. The thing that has changed is the display.

 

I can create bands on my Viewsonic by only inserting the CHROMA plug part-way, leaving the signal un-grounded. This makes color clock bands on the LUMA from bad signal on the CHROMA. The TV is doing this, not the Atari. If I insert the CHROMA plug properly, I get a clean display.

 

Try disconnecting both the modulator and COMPOSITE links. Just lift the resistors at one end.

 

I can't recommend hacking up your 800 just to make it work on a couple of quirky TVs, however.

 

Bob

[Faicuai]

I honesly differ a bit from the "it's the monitor, not the Atari" conclusion.

 

However, and before arguing qualitatively on the subject, I will try to find sometime (maybe this weekend, I hope) to hook-up my Fluke Scopemeter (capable or tracing NTSC signal, per-scan-line) and measure/graph LUMA response on a solid-color screen (displayed at low, mid and hi luma-values), directly from the video-port.

 

Once I get these measures, I will post here the Scope's graph. The Scopemeter won't lie: if there is contamination on Luma signal, it will SHOW UP at the "roof" part of highest voltage-level graph, for any given brightness level. However, if that "roof" of the graph shows up as serrated / garbled, there will be Luma/Y signal contamination, right from the Atari, beyond the shadow of doubt.

 

This will be true because (coincidentally) the banding pattern we are exploring appears as a VERTICAL pattern crossing from top-top-bottom each scan-line, while the scan-line response itself is traced HORIZONTALLY, thus any disturbance invariably showing on the Scan-Line graph of the Scopemeter, if it exists there.

 

As a reference, I have seen this exact same output from a reference signal (DVD, solid-color screen, multiple brightness levels, on sVideo) and, in all cases, the Luma/Y signal appear beautifully clean and flat, at the top (highest-voltage level).

 

We'll see who's who, then.

[flashjazzcat]

I'm with Bob here to a large extent. Got so many monitors here and get drastically different results with many of them. You can expend a lot of time and energy (and I have) tailoring an A8's video output to look good on one monitor, only to plug it into a 1084S one day and find the picture's ruined on the older display. Been there and done it, as I say.

[+Stephen]

I honesly differ a bit from the "it's the monitor, not the Atari" conclusion.

 

However, and before arguing qualitatively on the subject, I will try to find sometime (maybe this weekend, I hope) to hook-up my Fluke Scopemeter (capable or tracing NTSC signal, per-scan-line) and measure/graph LUMA response on a solid-color screen (displayed at low, mid and hi luma-values), directly from the video-port.

 

Once I get these measures, I will post here the Scope's graph. The Scopemeter won't lie: if there is contamination on Luma signal, it will SHOW UP at the "roof" part of highest voltage-level graph, for any given brightness level. However, if that "roof" of the graph shows up as serrated / garbled, there will be Luma/Y signal contamination, right from the Atari, beyond the shadow of doubt.

 

This will be true because (coincidentally) the banding pattern we are exploring appears as a VERTICAL pattern crossing from top-top-bottom each scan-line, while the scan-line response itself is traced HORIZONTALLY, thus any disturbance invariably showing on the Scan-Line graph of the Scopemeter, if it exists there.

 

As a reference, I have seen this exact same output from a reference signal (DVD, solid-color screen, multiple brightness levels, on sVideo) and, in all cases, the Luma/Y signal appear beautifully clean and flat, at the top (highest-voltage level).

 

We'll see who's who, then.

Excellent - it will be interesting to see just how out of spec the signal really is.

[crash]

Analyze what you are saying: it worked on older displays - it does not work (has bands) on many different Atari sources. The thing that has changed is the display. I can't recommend hacking up your 800 just to make it work on a couple of quirky TVs, however.

 

My concern is that the S-Video signal from these older devices is incompatible with modern devices. I have a Pioneer TV and a Samsung TV, which are pretty mainstream brands. The fact that the initial poster had the exact same banding pattern that was resolved by a modification to the Atari tells me that there is something going on that may not be specific to my TVs. While it could be the cables, I had not been paying much attention to that possibility since it occurs with two factory made S-Video cables and one home-made monitor cable. It has seemed that the problem was in the signal itself.

 

Also worth mentioning, is that the banding still occurs whether I run the S-Video directly to the TVs, or first through the receiver, through a VCR, or through an S-Video amplifier with various adjustments, and combinations of these. The other thing that gives me reason to question the S-Video signal, is that when running it through the receiver, it is very difficult to get any picture at all. The built-in i/p converter/scaler does not recognize the S-Video signal, or the picture turns on an off, or the screen flashes white static with most settings. The documentation for the receiver states the following (at least three times:

 

"When a non-standard video signal from a game machine or some other source is input, the video conversion function might not operate."

 

This seems to be a known issue. I had mentioned before that when I did a google image search for some of the terms, I kept getting Atari pictures. I tried a few combinations of those searches, and came up with the following discussions that seem to describe various Atari users experiencing the same problems on differing models of television and computer. This seems to be a widespread problem. At least a few places mention modifications to the S-Video cable that can resolve this, although it will take me some time to go through all of these threads to look for a consensus.

 

http://www.realdos.net/UltraVideo%20xe.html

http://atariage.com/forums/topic/145007-perfect-all-in-one-monitor-for-ataris-and-pcs/

http://atariage.com/forums/topic/175101-800xl-video-issues/

http://atariage.com/forums/topic/206988-can-anyone-in-the-us-to-a-vbxe-install-for-me/

http://atariage.com/forums/topic/159964-43-pal-lcd-tvs-for-the-atari-8/

http://atariage.com/forums/topic/116010-8bit-on-vga-with-s-video/?hl=Chroma+resistor

http://atariage.com/forums/topic/190802-lcd-tv-for-atari-8-bit/page-2

http://atariage.com/forums/topic/206988-can-anyone-in-the-us-to-a-vbxe-install-for-me/

http://atariage.com/forums/topic/161962-xegs-monitor-port/

http://atariage.com/forums/blog/341/entry-7686-nasty-a8-output-on-modern-lcd-tv/

http://atariage.com/forums/topic/155245-vertical-lines-on-many-xe-computers/

http://atariage.com/forums/topic/144522-lcd-tv-choice/page-2

http://atariage.com/forums/topic/194052-old-ataris-on-modern-tvs/

http://atariage.com/forums/topic/175101-800xl-video-issues/

http://atariage.com/forums/topic/116010-8bit-on-vga-with-s-video/page-2

http://atariage.com/forums/topic/215864-weird-color-s-video-on-a-stock-800xl/

http://atariage.com/forums/topic/178089-kjmann-s-video-upgrade/

http://atariage.com/forums/topic/157888-ultravideo-10-xe/

http://atariage.com/forums/topic/178156-remove-rf-modulator/

http://atariage.com/forums/topic/188545-600xl-video-upgradekjmann-v20-s-video/?do=findComment&comment=2694838

 

Thanks!

[crash]

This will be true because (coincidentally) the banding pattern we are exploring appears as a VERTICAL pattern crossing from top-top-bottom each scan-line, while the scan-line response itself is traced HORIZONTALLY, thus any disturbance invariably showing on the Scan-Line graph of the Scopemeter, if it exists there.

 

In case this gives any insight, a few of the threads describe the vertical bands as "clock lines". I will be most appreciative of your willingness to look into this with your scopemeter.

 

Thanks!

[crash]

I'm with Bob here to a large extent. Got so many monitors here and get drastically different results with many of them. You can expend a lot of time and energy (and I have) tailoring an A8's video output to look good on one monitor, only to plug it into a 1084S one day and find the picture's ruined on the older display. Been there and done it, as I say.

 

I can tell you that the last thing I want to do is modify my original Atari 800. I would not be willing to do this if the modifications were only effective for one TV or monitor, but if there is something that can be done to eliminate this problem for all displays, then I think it is worth doing. I don't see myself going back to a 12 inch composite crt.

 

Thanks!

[+bob1200xl]

The Atari definitely has non-standard video. But, old analog TVs and monitors didn't really care and produce a good display.

 

The banding that is caused by color clock on the LUMA line shows up on all displays, analog and digital. You can resolve that issue by disconnecting the CHROMA feed to the COMPOSITE circuits, as Faicuai states in the beginning of this thread. He also states, however, that he was not able to resolve banding on an 800 with this procedure.

 

Some digital monitors or TVs work fine, some do not. We just have to live with that. Unless you want to add a VBXE-type hack.

 

On your cables: there are no 'factory' s-video cables for the Atari. How do you convert from the 5-pin DIN on your 800 to a s-video connector? I make a little box with RCA sockets for the LUMA and CHROMA from the Atari and wire the two cables in a s-video cable to the RCA sockets. I do not wire the returns together. I don't know if this matters or not...

 

This whole video thing is a ball of snakes. You will find lots of fixes and lots of opinions - bottom line is that there aren't any good answers.

 

Bob

 

 

 

 

My concern is that the S-Video signal from these older devices is incompatible with modern devices. I have a Pioneer TV and a Samsung TV, which are pretty mainstream brands. The fact that the initial poster had the exact same banding pattern that was resolved by a modification to the Atari tells me that there is something going on that may not be specific to my TVs. While it could be the cables, I had not been paying much attention to that possibility since it occurs with two factory made S-Video cables and one home-made monitor cable. It has seemed that the problem was in the signal itself.

 

Also worth mentioning, is that the banding still occurs whether I run the S-Video directly to the TVs, or first through the receiver, through a VCR, or through an S-Video amplifier with various adjustments, and combinations of these. The other thing that gives me reason to question the S-Video signal, is that when running it through the receiver, it is very difficult to get any picture at all. The built-in i/p converter/scaler does not recognize the S-Video signal, or the picture turns on an off, or the screen flashes white static with most settings. The documentation for the receiver states the following (at least three times:

 

"When a non-standard video signal from a game machine or some other source is input, the video conversion function might not operate."

 

This seems to be a known issue. I had mentioned before that when I did a google image search for some of the terms, I kept getting Atari pictures. I tried a few combinations of those searches, and came up with the following discussions that seem to describe various Atari users experiencing the same problems on differing models of television and computer. This seems to be a widespread problem. At least a few places mention modifications to the S-Video cable that can resolve this, although it will take me some time to go through all of these threads to look for a consensus.

 

http://www.realdos.net/UltraVideo%20xe.html

http://atariage.com/forums/topic/145007-perfect-all-in-one-monitor-for-ataris-and-pcs/
http://atariage.com/forums/topic/175101-800xl-video-issues/
http://atariage.com/forums/topic/206988-can-anyone-in-the-us-to-a-vbxe-install-for-me/
http://atariage.com/forums/topic/159964-43-pal-lcd-tvs-for-the-atari-8/
http://atariage.com/forums/topic/116010-8bit-on-vga-with-s-video/?hl=Chroma+resistor
http://atariage.com/forums/topic/190802-lcd-tv-for-atari-8-bit/page-2
http://atariage.com/forums/topic/206988-can-anyone-in-the-us-to-a-vbxe-install-for-me/
http://atariage.com/forums/topic/161962-xegs-monitor-port/
http://atariage.com/forums/blog/341/entry-7686-nasty-a8-output-on-modern-lcd-tv/
http://atariage.com/forums/topic/155245-vertical-lines-on-many-xe-computers/
http://atariage.com/forums/topic/144522-lcd-tv-choice/page-2
http://atariage.com/forums/topic/194052-old-ataris-on-modern-tvs/
http://atariage.com/forums/topic/175101-800xl-video-issues/
http://atariage.com/forums/topic/116010-8bit-on-vga-with-s-video/page-2
http://atariage.com/forums/topic/215864-weird-color-s-video-on-a-stock-800xl/
http://atariage.com/forums/topic/178089-kjmann-s-video-upgrade/
http://atariage.com/forums/topic/157888-ultravideo-10-xe/
http://atariage.com/forums/topic/178156-remove-rf-modulator/
http://atariage.com/forums/topic/188545-600xl-video-upgradekjmann-v20-s-video/?do=findComment&comment=2694838

 

Thanks!

[crash]

With regard to the factory s-video cables, I was referring to regular s-video cables I've tried with the 7800 which has the same vertical banding. The monitor to s-video cable I have is homemade, although I ordered one online that should be here soon. I didn't know about the monitor to rca cable, and will have to get one of those for testing. I see that B&C offers both items, the monitor port to chroma/luma cable, and the chroma/luma to s-video adapter.

 

Thanks

[Faicuai]

Ok. So here's what I did:

1. I fired up one 800XL, as well as my Incognito-800
2. Loaded a custom basic program (where I can set separate LUMA and CHROMA values for whole-screen)
3. Setup my Fluke 99B-SeriesII Scopemeter, set to Video(NTSC, Positive, ScanLine=40) trigger.
4. Sampled signals from both Atari's VIDEO port (both machine have sVideo output enabled).

 

Here are the results, per machine:

 

I. Reference unit, ATARI 800-XL (NTSC, RevC-HongKong, socketed, ALPS-keyboard, C54 in-line switch):

 

(actual C54 in-line switch / scope-trace with C54=OFF (=>no on-screen banding) / scope trace with C54=ON (=>on-screen banding):

 

 

NOTES:

• Notice above the overall signal amplitude: approx. ~1.78v Peak-to-Peak, Max=~2.38v, Min=~0.7v (certainly higher than sVideo typical specs).
• Notice the SERRATED / teeth-like top-line of the ChromaON signal trace (that line shows what is happening to Luma values INSIDE of ScanLine 40, itself, after enabling Chroma-combination point in C54-circuit). On my basic program, Luma was set to MAX (value=15) and Chroma cycled through any of the 15 possible values, as well.

 

II. Target unit, ATARI 800 (NTSC, USA, ~1982, R189 @ 220Ohm, NO in-circuit isolation of any Y/C combining points):

 

On the Incognito-800, we play with enabling chroma output via SOFTWARE: from my Basic program, I took signal-trace sample with LUMA=15, CHROMA=0 (first image), and then I cycled chroma through ANY values, and traced-again (second image):

 

 

Below are ZOOM samples on the Scan-Line trace, so effects can be seen better:

 

 

NOTES:

• Notice signal amplitude: approx. ~3.80v Peak-to-Peak (!!!), Max=~3.90v, Min=~0.18v (TOTALLY out of boundaries of sVideo typical specs, even with 220 Ohm R189!).
• Due to the much higher voltage-levels, I turned the Scopemeter's Glitch-On feature, so we could better distinguish the relatively smaller variations at top-level of Scan-Line trace.
• Plenty of banding with shown on the 800's output. And it is clear that the LUMA signal is CONTAMINATED right from the get-go.
• I honestly can't complain for a 1979 machine to output banding on its Luma-channel, considering that I do not recall consumer Y/C video interfaces being available, back then. It is a blessing, already, that we can extract such signal easily and with minimal or no mods, right from the original physical config. of the 800.

 

All-in-all, and after researching for quite some time on this subject (trying to fix my own problems), I have noticed and overall lack of technical / objective analysis of the Atari's video circuitry and output itself. SURE you will find plenty of personal / empirical / subjective recipes, fixes, etc., but very little factual data that helps identifying (better) potential root-causes.

 

Just my 0.02c, though.

[crash]

Is it possible to sample back through the Luma circuit with your scope to find the point where the contamination first appears, or something to that effect? I'm a novice, but it seems to me that the problems may be with a video circuit that is attempting to output three types of video (composite, C/L, and RF), and that these are not completely isolated aka discrete, so there may be crosstalk or contamination. Does your working modification from the initial post disable one or more of the other output types?

 

Thanks

[crash]

Plug the LUMA cord into the COMPOSITE jack. Any color at all? Better not be.

 

Hi,

 

My cable is wired from the 5-pin monitor directly to S-Video, but as a test I connected an RCA cable to Pins 1-Luma and 2-Ground and connected the RCA to a composite video input. Assuming that this corresponds to what you suggest... there IS color with only these two connected. Next, I went back to the monitor cable, and disconnected only the Chroma wire, then plugged the S-Video cable back in. Here, I get no color, but, the vertical banding is still present even in grayscale. Does this mean that the interference/contamination is on the Luma signal?

 

Thanks

Edited September 16, 2013 by crash

[+bob1200xl]

Yes, it does. The LUMA circuit has color information from the CHROMA circuit present.

 

Did you try disconnecting both CHROMA paths at the same time? (one to COMPOSITE and one to the modulator)

 

Bob

[crash]

Would this be both R202 (Chroma/composite link) and R206 (Chroma/RF modulator link)? I only tried the first one so far.

 

Looking at the schematic, there is a connection between Luma, Mod, and Composite lines at R200. Could that be a problem?

Thanks!

[+bob1200xl]

R200 is in the LUMA circuit. Lift one side of R202 and R206 at the same time and try it.

 

Try turning down your Sharpness control on your TV.

 

The issue isn't in the 800. The problem lies in the TV converting the analog video to digital video. Normally, you would normalize the video signal in order to compensate for different voltage swings. You then place the sync tip at 0v and look for the 'back porch' where the color burst should be. Next comes the video black level which should be .3v or some such. White LUMA should be 1.0v, I think.

 

Anyway, the Atari doesn't meet specs for video. Some TVs and monitors can't even set up for an Atari and you get a black screen. Others work just fine. Some give you banding, probably as a result of too much 'normalization' and overly aggressive video processing.

 

On the Viewsonic that I tried, no banding was evident unless I only inserted the RCA plug tip into the socket, leaving the shield/ground/return open circuit. This probably upset the normalization circuits because the reference levels were floating and the return path was forced into some other part of the circuits. As a result, I got banding. Push the plug in all the way and it looked fine.

 

Anyway, try R202 and R206. That may lower the CHROMA level so that banding will not be an issue. Or, try cutting down on sharpness - that just amplifies the color clock noise.

 

Bob

[crash]

Disconnecting both has no effect. Adjusting the sharpness controls all the way to zero has no apparent effect. When I referred to R200, I was wondering if it would help to disconnect the Luma circuit from the others. I have indicated on the schematic below with a blue line where I was thinking of:

 

Edited September 17, 2013 by crash

[Faicuai]

Disconnecting both has no effect. Adjusting the sharpness controls all the way to zero has no apparent effect. When I referred to R200, I was wondering if it would help to disconnect the Luma circuit from the others. I have indicated on the schematic below with a blue line where I was thinking of:

 

Video3.jpg

 

YES, complete isolation of LUMA would be ideal.

 

Then display Luma-only signal (on sVideo input of your screen), and check for banding. If no banding, then proceed to carefully enable each Chroma combination point, one-by-one while LOOKING at your screen, until you get banding (at this point is where you should install a switch for sVideo or Composite/RF output, similar to what I installed on my 800XL, above).

 

NOW, if you get banding on a bare-bones Luma signal, then the culprit is [the 800's unlawful video-signal levels] combined with how [YOUR screen handles it].

 

Solution: either normalize response/levels of 800's signal, or get yourself an DVDO iScan HD or HD+ video processor (there's one one on eBay now, running for $50 bucks). The latter will output a crisp and beautiful DVI signal that you can pre-process on-board the iScan and its slew of fine-tuning options. It will also spare your 800 from any further butchering, and you will never look back.

 

Enjoy!

[crash]

Just for the sake of it, I also disconnected C163 and R200, also with no effect.

 

Where is the earliest point in the Luma circuit that I can test?

 

Thanks!

[BillC]

As long as R202/R206 are disconnected there shouldn't be any Chroma signal present to pass through R200 to contaminate Luma, the only other connections to the Chroma signal are C174/R204 to ground. The only other possibility I can think of is that common pads for C174/C176 have become disconnected from ground(broker trace/bad solder joint?) and the Chroma signal is able to feed through both of them instead of to ground. There is no resistor on this path to reduce the Chroma signal either.

Would this be both R202 (Chroma/composite link) and R206 (Chroma/RF modulator link)? I only tried the first one so far.

 

Looking at the schematic, there is a connection between Luma, Mod, and Composite lines at R200. Could that be a problem?

Thanks!

[crash]

Okay, I tested C174/R204 to ground, both of which are good. I disconnected C174/C176 because why not, and there was no change. I'm baffled.

 

It looks like Luma is completely isolated at this point, but maybe I'm wrong. Here is a schematic indicating the disconnections in blue:

 

 

I tried tracing the Luma circuit backwards and tapping in a few places, but anything before R189 makes the screen too bright to see anything including potential vertical bands.

 

Finally, with all of these components disconnected, I again tried the test of connecting the Luma pin and ground to an RCA plug into the composite video port. It is still in color! For whatever reason, the Luma line seems to be mixed with color and I haven't been able to de-couple this.

 

Considering the possibility that the problem may be completely unrelated to what I've been assuming... I was looking at some other discussions that suggest this banding is due to cycling voltage fluctuations. Does that give any insight? These are the comments from different threads:

 

"After Building my S-Video Upgrade kits (version 1.0), I started tinkering with this issue. What I found is that the Culprit behind the lines showing up is the lack of full voltage to one of the transistors in the original Atari video circuit. With this in mind I built the S-Video Upgrade Version 2.0, Which actually has it's own transistor on board and bypasses the original Atari luma circuit altogether. because of this I had to require the version 2.0 board to be powered (so It gets +5 from a spot near the power switch inside the Atari). but, It Definitely solved the problem. =)"

 

"This "vertical banding" is a result of "voltage reducing" when the DMA is done-> the brightness gets lower during those events."

 

Thanks!

[+bob1200xl]

Bands from DMA look different than the color clock bands. You don't have DMA 'noise'.

 

I would guess that lifting R200 would break the LUMA circuit because R200 is in the emitter resistor pair. Since it does not, there is either another path or you have the wrong R200.

 

Even if there are no paths for CHROMA to reach the LUMA circuits you can still get color clocks impressed on ground. That's a little tougher to fix.

 

Bob

[crash]

Hi,

 

I'm pretty sure it is the correct R200, since the open pad is connected to R189. Don't know about other paths. Maybe I need a diode somewhere?

 

Any idea how I'm still getting color over Luma?