Any solution for the colour bleed caused by the composite mod?

[+save2600]

I think my biggest issue right now is that vertical line in Ms Pacman during audio

 

 

...that happens on an early 4-switch 2600 of mine too, only my system has not been modded. Can't say I recall any other game wigging out like that, so must be something nasty in that particular sound in Ms. Pac-Man that invokes the vertical line of agitation.

[rednakes1]

 

 

...that happens on an early 4-switch 2600 of mine too, only my system has not been modded. Can't say I recall any other game wigging out like that, so must be something nasty in that particular sound in Ms. Pac-Man that invokes the vertical line of agitation.

 

 

Hmm I didn't notice the problem when it was unmodded (I play a lot of Ms Pacman), but perhaps it was masked by the RF static. You may be right and it may be one of the original components not acting well..

Edited November 3, 2016 by rednakes1

[+save2600]

Not a huge deal, but would be nice to find what component is to blame for this. The line comes and goes during certain sequences is all. Certain tones, screen mode or something. For example: while eating ghost monsters and at the start of a level after "dying".

[rednakes1]

Not a huge deal, but would be nice to find what component is to blame for this. The line comes and goes during certain sequences is all. Certain tones, screen mode or something. For example: while eating ghost monsters and at the start of a level after "dying".

 

 

Possibly the reason is the amount of volume coming out of the Atari, which is causing interference in the game? I am suspecting this could be the reason, because today I tried my Colecovision Expansion Module 1 with my Atari games, and then compared the same games on the Atari 2600 4-Switch. The Coleco had no issue issue with Ms. Pacman, and the volume in comparison was noticeably louder on the Atari 2600. Possibly the amount of audio amplification is causing interference somehow in Ms. Pacman.

 

So my question is, how do we adjust the audio amplification? I'm guessing R206 could be replaced with a bigger resistor?? No idea...

 

 

As an aside, my Coleco Expansion Module 1 looks great after the A/V mod on the Colecovision. Sharper than the video with the Atari mod, which looks a bit too soft. However the Coleco also shows the colour bleed with Jr. Pacman, so maybe it's not too big a deal then.

Edited November 4, 2016 by rednakes1

[rednakes1]

Okay so here's what I've done in the last little while. No improvements yet but I thought I'd share:

 

 

The colour bleed is worse than I thought; I guess when I compare it to my Colecovision Expansion Module 1 it is more obvious. Text is not sharp, graphics are a bit blurry too as a result.

 

- removing C215 increases the jailbar effect noticeably (this cap is one of the last components that feeds into the Video Out line)

 

- Removed the big ugly RF box finally - no effect as expected, but just wanted to make sure

 

- Colour bleed makes games like Radar Lock look really bad, blurry and almost unplayable (compared to how it looks on the Flashback 2, it makes me sad!)

 

- Regarding the sound interference issue in Ms Pacman, disconnecting the wire for Audio Out from the main board still doesn't prevent the vertical line when sound is supposed to be played. Tested on both Harmony Cartridge and original cartridge, same issue.

 

- Added a 75 Ohm resistor to bridge Video Out to Ground, but it made no difference to colours or brightness or the Ms Pacman issue (it's recommended for impedance matching, and used in some schematics)

 

I wonder if there's anything else I should look at, such as the three Luma lines from the TIA?

[ApolloBoy]

Honestly I would ditch that mod and get one of the mod boards here. I've tried the simple composite mod on a few systems (a 2600 Jr., a Vader and a 7800), and I never had consistent or satisfactory results with any of them.

[RevEng]

Does the mod have a decoupling capacitor? If not, try adding one.

[rednakes1]

Does the mod have a decoupling capacitor? If not, try adding one.

No I didn't use a capacitor. What amount should I use and where should I put it? I'm attaching a schematic of the AV mod, which I got from another post.

[rednakes1]

Honestly I would ditch that mod and get one of the mod boards here. I've tried the simple composite mod on a few systems (a 2600 Jr., a Vader and a 7800), and I never had consistent or satisfactory results with any of them.

Yeah I could try that but I don't want to throw more money at this little project right now. I want to see if I can get anything out of the one I bought, and try to understand what's going wrong so that another mod in the future doesn't show the same symptoms. Thanks for your input though.

Edited November 6, 2016 by rednakes1

[RevEng]

Picking a value for decoupling caps is a bit of an art, but 0.1 uf is typical starting point. Stick it across the GND and +5V. It's used to isolate noise from the local circuit, and could help with the Ms Pac audio bleeding into the video.

I'm not expecting any real change with the chroma issue... usually 2600 chroma artifacts are a matter of chroma being ahead of luma, or visa versa. Here it looks like the chroma frequency response is somehow being smeared, with green delayed after red.

Also, does it look like that on all of your TVs? [edit - I see you mentioned that earlier. Nevermind]

[rednakes1]

Picking a value for decoupling caps is a bit of an art, but 0.1 uf is typical starting point. Stick it across the GND and +5V. It's used to isolate noise from the local circuit, and could help with the Ms Pac audio bleeding into the video.

I'm not expecting any real change with the chroma issue... usually 2600 chroma artifacts are a matter of chroma being ahead of luma, or visa versa. Here it looks like the chroma frequency response is somehow being smeared, with green delayed after red.Also, does it look like that on all of your TVs? [edit - I see you mentioned that earlier. Nevermind]

The lowest cap I have is 1uF, which I reused from the RF connector board. I used it to bridge the 5V and Ground going into the video mod board, but it didn't seem to have any effect.

 

I haven't tried any other TVs. I actually tried connecting to one of my LCDs but somehow it didn't detect the AV connection. For now it's on my CRT TV which hasn't been giving problems on other AV devices (Colecovision, Atari FB2, PS2).

 

I haven't been up to speed on Luma/Chroma, how could I resolve the potential issue you mentioned?

Edited November 6, 2016 by rednakes1

[RevEng]

The lowest cap I have is 1uF, which I reused from the RF connector board. I used it to bridge the 5V and Ground going into the video mod board, but it didn't seem to have any effect.

Ok. The Ms Pac effect sounds like the audio is getting into the video signal, at least in part. I thought it might be through power/ground, but maybe not.

 

TBH I'm not sure about the chroma smear. I would have suggested trying impedance matching, since that might cause reflections that look like smearing, but you say you tried that.

 

Some troubleshooting of this sort of mod can be found on this page. I prefer the approach on that page - to lift chroma and luma as directly as possible, rather than tapping the joined signal on the console. Anyway, give that a read and see if there's any inspiration.

[hizzy]

Is the vintagegamingandmore mod the same as the Ben Heck mod?

[rednakes1]

Ok. The Ms Pac effect sounds like the audio is getting into the video signal, at least in part. I thought it might be through power/ground, but maybe not.TBH I'm not sure about the chroma smear. I would have suggested trying impedance matching, since that might cause reflections that look like smearing, but you say you tried that.Some troubleshooting of this sort of mod can be found on this page. I prefer the approach on that page - to lift chroma and luma as directly as possible, rather than tapping the joined signal on the console. Anyway, give that a read and see if there's any inspiration.

Thanks, it did give me some insight but it's a little too involved as I don't have all the parts on me (high resistor values and pots). It's also for PAL but mine is NTSC, so I don't know if things will be different.

 

However, I saw this thread as well:

http://assemblergames.com/l/threads/composite-atari-2600.48162/page-2

 

See the last post with the 15K resistor from R222 as well as the transistor at Q202 being reused. I'm actually going to prototype it on a breadboard and test it out when I have time. I took off R222 from my Atari and it had no effect on the current issue, so I will reuse it.

 

There is also a 100 Ohm resistor on the RF connector board that can be reused for this.

[rednakes1]

Is the vintagegamingandmore mod the same as the Ben Heck mod?

 

No this is Ben Heck's mod for the 4-switch:

http://benheck.com/classic/Question2.htm

[rednakes1]

Okay, so here's what I did just now on a breadboard, based on the schematic I linked 2 posts up. I hooked it up, and to my surprise, it actually showed an image. See the attachment for the version I made; I just tweaked the resistor values. (EDIT: I forgot to write that Audio also has a Ground on its jack, so don't forget to do that.) I used 120 Ohms instead of 100 Ohms, as it looked better, and I used 68 Ohms instead of 75 Ohms because that's all I had.

 

Here are the changes I had to do on my 4-switch Rev 13 board:

 

- Remove Q201 (or Q202) - this transistor will be reused for this mod

- Remove R222 - will be reused for this mod

- Remove RF circuit board and de-solder the pins from the holes

- Remove R209

- Remove C215 - if you keep it on the board you won't get a noticeable jailbar effect, but ghosting will be very bad

 

 

Some observations:

 

1) Colours are very vibrant with these resistor values. Looks great. If I remove either of the 120 or 68 Ohm resistors (or reduce the resistor value), the colours will come out very dull.

 

2) In Ms Pacman, the audio distortion effect (vertical line down the middle) still happens, but only once in a while. It's very random, in some sessions it shows up when you die, and in other sessions it doesn't show up at all. I tried moving wires around on the breadboard so that there wouldn't be any touching, but it was again still randomly happening.

 

3) The jailbar effect is caused by removing C215, but I had to do it, because otherwise the colours go dull and you see *major* ghosting: some colours such as pink or white leave a long ugly streak to the right of the graphic. But otherwise, with C215 the image would have looked smoother and with not much jailbars. So there's the trade-off. Currently the images look a bit pixelly; you can see the dots.

 

4) There's still bleeding of colours as before. Quick test: Just start up Adventure and look at the number "1". It has a shadow in a different colour, when it shouldn't have any shadow.

 

 

Currently I'm not entirely happy with this version as the images are not as clear due to removal of C215. But it's more colourful, and the Ms Pacman issue is not frequent. Other people may have better luck with their Atari. Plus you can save money if you decide to use it.

 

I wish I could add some samples of the games, but I have to shut down and go to bed.

Edited November 7, 2016 by rednakes1

[rednakes1]

So I spent some more time on this tonight. I'm not quitting! LOL

 

This time I decided to try another method. I wanted to get a cleaner picture, so I had to get the video directly from the TIA rather than through a bunch of intermediate components like my other methods were doing. So to start, I went with a simple one - Ben Heck's original mod (Rev 1), which is linked here for the 4-switch 2600:

 

http://benheck.com/classic/Question2.htm

 

 

 

 

I used the following values, as I didn't have potentiometers or 22 Ohm resistors:

 

TIA Pin 5 (Luma 1) connected to 480 Ohms*

TIA Pin 7 (Luma 2) connected to 68 Ohms

TIA Pin 8 (Luma 0) connected to 1000 Ohms

 

*Actually i have no idea what Luma 1 does, because when I removed it from my circuit it had exactly no effect. I even increased/decreased the resistor values and there was no difference.

 

I combined the above lines to Chroma (junction of R210/C210) and Sync (Pin 2) to get a composite signal to Video Out. No 5V source is required, so I'm assuming it won't work with all TVs if the signal is that weak. But it worked on my 13" CRT.

 

Anyways the results:

 

1) Colours are still bleeding

2) Jailbars (vertical banding) are still showing up

3) Fixed the Ms. Pacman sound interference issue. Woohoo!

 

 

I still want to fix #1 and #2. For the jailbars, probably I need a capacitor somewhere. Something like how C215 does for the other mods? I did try a 1uF capacitor between Video Out and Ground, but that made no difference.

 

I think tomorrow I'll go to the electronics store and pick up some more components to try a more involved approach. I'll try the link @RevEng gave me above, and use the resistor ladder + transistor amplifier method.

 

Or, if there's any other advice to fix up the mod that I just did, that would be appreciated!

 

 

 

 

 

[RevEng]

I used the following values, as I didn't have potentiometers or 22 Ohm resistors:

 

TIA Pin 5 (Luma 1) connected to 480 Ohms*

TIA Pin 7 (Luma 2) connected to 68 Ohms

TIA Pin 8 (Luma 0) connected to 1000 Ohms

 

*Actually i have no idea what Luma 1 does, because when I removed it from my circuit it had exactly no effect. I even increased/decreased the resistor values and there was no difference.

Each luma line represents 1 bit of luminance, so the 3 luma lines provide up to 8 shades of luminance for any displayed color on the screen. You may not have seen a difference without luma1 in whatever game you tested with, but the color shades displayed were likely not the intended ones. If you view a game that does the classic colorbars effect, or even just color cycling (like the chalice in Adventure) the color changes won't be smooth, making the difference easier to see.

 

The luma resistor ladder is a digital-to-analog converter. The actual values don't matter very much, but the relative values do. Each luma resistor should be half the resistance of the previous one. If you don't follow that rule then the luminance values will be messed up - subtly wrong if you're close to the correct ratio, less subtly if you're way off.

[alex_79]

If you have an "Air-Sea Battle" cart, start the game with RESET and flip the TV TYPE switch to "B/W".
The sky in the game will show all 8 shades of luma from black to white.
If there are less than 8 shades, or if they are not in the right order , then something is wrong with your mod (less than 8 shades might also be the result of a bad TIA).

Edited November 8, 2016 by alex_79

[rednakes1]

If you have an "Air-Sea Battle" cart, start the game with RESET and flip the TV TYPE switch to "B/W".

The sky in the game will show all 8 shades of luma from black to white.

If there are less than 8 shades, or if they are not in the right order , then something is wrong with your mod (less than 8 shades might also be the result of a bad TIA).

 

Air-Sea Battle (1977) (Atari).png

Thanks for the tip. I am probably setting the values wrong or my TIA is not good.

 

EDIT: Never mind, I noticed my Pin 5 was tied to 120 Ohms rather than 480. My mistake. The shades look better now.

Edited November 8, 2016 by rednakes1

[rednakes1]

Each luma line represents 1 bit of luminance, so the 3 luma lines provide up to 8 shades of luminance for any displayed color on the screen. You may not have seen a difference without luma1 in whatever game you tested with, but the color shades displayed were likely not the intended ones. If you view a game that does the classic colorbars effect, or even just color cycling (like the chalice in Adventure) the color changes won't be smooth, making the difference easier to see.The luma resistor ladder is a digital-to-analog converter. The actual values don't matter very much, but the relative values do. Each luma resistor should be half the resistance of the previous one. If you don't follow that rule then the luminance values will be messed up - subtly wrong if you're close to the correct ratio, less subtly if you're way off.

Don't you need a specific minimum value for the resistor ladder?

 

Also, could potentially a replacement TIA fix my bleeding issues?

[RevEng]

Don't you need a specific minimum value for the resistor ladder?

Also, could potentially a replacement TIA fix my bleeding issues?

The minimum value depends on how strong the combined Luma signal should be compared to the sync and chroma levels. Use the values in the mod I linked to earlier as a starting point.

 

I don't think it's likely that a bad TIA is causing the chroma smear, though anything is possible. Since you've only tested on one TV, it may be it's chroma detection circuit is ringing from a too strong chroma signal. Or it may be bad caps in 2600 colorburst generation. Not sure what else it might be, as you're now lifting chroma straight from the TIA COL pin.

[Papa]

I thought that something else controlled these offset lines when the mod is done. A pot before modding. I just went back to original RF (yet another CRT to test on) and was pleasantly surprised at how nice everything looked when there is little to no interference. Our problem with modding (and this created effects not dissimilar to yours) ended up being immediately fixed by reverting to original power supplies. These new ones mess my systems up.

[rednakes1]

I thought that something else controlled these offset lines when the mod is done. A pot before modding. I just went back to original RF (yet another CRT to test on) and was pleasantly surprised at how nice everything looked when there is little to no interference. Our problem with modding (and this created effects not dissimilar to yours) ended up being immediately fixed by reverting to original power supplies. These new ones mess my systems up.

 

You mean the color pot that adjusts the tint after the mod is wired up? Yeah I've done that.

 

I am using an Atari power supply; I did try a cheap one from eBay but I kept getting a horizontal rolling static.

[rednakes1]

I've managed to reduce some of the colour bleeding and a little of the jailbar effect to the Ben Heck mod I had been trying. It has also added a bit of colour vibrancy. See the attached image for the Before and After, it's from the menu of my Harmony Cartridge being displayed on my CRT TV.

 

All I did was use a 1000pF capacitor which I took from the disconnected RF connector board, labeled "102" (I originally thought it was 0.1uF but it's actually 0.001 uF). I used it to bridge together the Video Out line to Ground. I did try 0.1uF instead but it caused the picture to get corrupted into white streaks on black background.

 

This seems similar in implementation to the C215 (150pF?) capacitor on the motherboard that helps smoothen the picture in the 2-resistor + 1 transistor mod which I had originally tried in this thread. I believe that capacitor also goes to ground and then feeds into the Video Out line.