easier 7800 Composite video mod

[puppetmark]

I'm also getting really tire of pulling the metal sheilding off the mobo, and replacing it every time. what a pain in the ass that is.

 

Just toss it. Once you get it modded, you don't really have any need for it anymore. I actually did this with some of my other systems and they work just fine.

 

Is this true? puppetmark?

 

I suppose it makes sens the metal sheilding was to prevent interference from getting in the the RF... anyone?

 

The metal sheilding on all Atari systems was designed to work both ways. It keeps out RF interference as well as keeps the RF it generates from interfering with TV, radio, ect. It was required to pass FCC testing. Now, with that said, if the modulators are not active, I don't see any reason why it can't be discarded. actually, I run my 130XE, XEGM, and 500ST all with out the top sheild and they all have working modulators ( even though I dont use them). I keep the bottom sheilds on because I think it helps make the boards more rigid especially the larger ones like the 520ST.

 

The RF modulator can be removed from the 7800 if it is not going to be used anymore but Underball is right, it can be a challenge to get out. You will need something like a 45 watt soldering iron to melt the large solder contacts that goto the RF modulator's casing. Another possibility might me a cut-off wheel on a dremmel tool and a steady hand.

 

BTW, the 130XE / 65XE uses the modulator to help generate the composite video signals, so it can't be removed. That is the only Atari system I know of that is like that. -Just an interesting side note.

[pepax]

Also, if my other 7800 has no expansion port, I will try to build a Svideo output from the port signals.

An "easier 7800 S-Video mod", (preferrably PAL ), that would be so nice!

I'm about to get a French (SCART-equipped) 7800 and I've been told that even the composite video looks better than this French RGB stuff... I wonder if it's really so bad.

[+Mitch]

Also, if my other 7800 has no expansion port, I will try to build a Svideo output from the port signals.

An "easier 7800 S-Video mod", (preferrably PAL ), that would be so nice!

I'm about to get a French (SCART-equipped) 7800 and I've been told that even the composite video looks better than this French RGB stuff... I wonder if it's really so bad.

 

I'm not sure who told you that, maybe someone with a bad unit. Both of my SCART 7800s have very excellent picture quality.

There's nothing like playing Combat in glorious RGB.

 

Mitch

[ApolloBoy]

OK, I finally got around to doing the mod today and I've followed the instructions to the letter (except that I used shielded cable instead of jacks and I got 5V from the RF modulator), but I've got a rather serious problem in terms of video quality. The audio is crystal clear, but the video has very bad artifacting, worse than a Sega Genesis. I don't know what's causing it, and the video amp circuit I built is solid. What could be causing this?

 

Edited July 21, 2008 by ApolloBoy

[puppetmark]

OK, I finally got around to doing the mod today and I've followed the instructions to the letter (except that I used shielded cable instead of jacks and I got 5V from the RF modulator), but I've got a rather serious problem in terms of video quality. The audio is crystal clear, but the video has very bad artifacting, worse than a Sega Genesis. I don't know what's causing it, and the video amp circuit I built is solid. What could be causing this?

 

Hmmm. I am not sure. It looks like a convergence problem. I need a little more info.

1.Which version of 7800 do you have?

2. Where did you pick up the video signal?

3. Did you disconnect the RF modulator.

4. Are you using a CRT or Flat panel TV?

[ApolloBoy]

Hmmm. I am not sure. It looks like a convergence problem. I need a little more info.

1.Which version of 7800 do you have?

2. Where did you pick up the video signal?

3. Did you disconnect the RF modulator.

4. Are you using a CRT or Flat panel TV?

 

1: I have the third version (no expansion port and no indentation)

2: I picked up the signal from the expansion port, as shown in the instructions.

3: The RF modulator is disconnected, although I'm picking up 5V from one of the modulator pins.

4: I'm using an LCD computer monitor hooked up to a TV tuner box. I tried a flat panel CRT and got the same problem.

Edited July 21, 2008 by ApolloBoy

[Underball]

4: I'm using an LCD computer monitor hooked up to a TV tuner box. I tried a flat panel CRT and got the same problem.

I'd be willing to bet this is the problem. TV tuner boxes tend to overscan and over-draw the image in many cases to fill in teh gaps with interlaced sources like composite video.

[ApolloBoy]

4: I'm using an LCD computer monitor hooked up to a TV tuner box. I tried a flat panel CRT and got the same problem.

I'd be willing to bet this is the problem. TV tuner boxes tend to overscan and over-draw the image in many cases to fill in teh gaps with interlaced sources like composite video.

 

Yes but as I said before, I also tried the 7800 on a flatscreen CRT and got the exact same result. The artifacting is so bad that small or white-colored text is practically unreadable.

Edited July 21, 2008 by ApolloBoy

[Underball]

4: I'm using an LCD computer monitor hooked up to a TV tuner box. I tried a flat panel CRT and got the same problem.

I'd be willing to bet this is the problem. TV tuner boxes tend to overscan and over-draw the image in many cases to fill in teh gaps with interlaced sources like composite video.

 

Yes but as I said before, I also tried the 7800 on a flatscreen CRT and got the exact same result. The artifacting is so bad that small or white-colored text is practically unreadable.

bad soldering? Try getting the video off the prong for the RF instead.

[ApolloBoy]

Try getting the video off the prong for the RF instead.

 

That might actually work, I think. This is a bit OT, but when I tried getting 5V off the expansion port, I got something like 3V, which caused the picture to roll. Perhaps the video from the expansion port isn't strong enough to give a good signal.

[puppetmark]

Try getting the video off the prong for the RF instead.

 

That might actually work, I think. This is a bit OT, but when I tried getting 5V off the expansion port, I got something like 3V, which caused the picture to roll. Perhaps the video from the expansion port isn't strong enough to give a good signal.

 

This is very puzzling. I am sorry you are having this issue. I get 5V from the expansion port but I think picking up the video signal at the RF modulator is a good suggestion. The amp in the mod is just an emitter-follower amp and really only amplifies what it "sees". Did you have artifacting isues before you instaled the mod? It may have been hard to tell through the RF. Does this happen with 2600 and 7800 games? Did you try to adjust the color Potentiometer. turning it very slightly might help.

[Underball]

I found when doing mine that trying to solder to the expansion port spots on the mobo was extremely difficult. I have a "version 3" no expansion post/no hole in case as well. This is because they are just unused spots on the board. Flat, smooth. Cutting away the board connected to the back of the RF box, and soldering to the cut off pins from where the RF unit connected to the Mobo was much easier, as there was something sticking up, something tactile to solder to.

[ApolloBoy]

This is very puzzling. I am sorry you are having this issue. I get 5V from the expansion port but I think picking up the video signal at the RF modulator is a good suggestion. The amp in the mod is just an emitter-follower amp and really only amplifies what it "sees". Did you have artifacting isues before you instaled the mod? It may have been hard to tell through the RF. Does this happen with 2600 and 7800 games? Did you try to adjust the color Potentiometer. turning it very slightly might help.

 

No, I didn't really have any artifacting issues with RF. I tried a 2600 game when I was testing the mod and got the same issue, though not quite as bad. I tried adjusting the color pot, but it didn't help.

[puppetmark]

No, I didn't really have any artifacting issues with RF. I tried a 2600 game when I was testing the mod and got the same issue, though not quite as bad. I tried adjusting the color pot, but it didn't help.

 

Did you double check and make sure you removed the correct resistors R3? There really is not much to the color circuit on the 7800. The color signals come from the TIA amd MARIA chips and pass through a resistor and then a coil (L1). After that it joins the luma output via C8 (47pf). Maybe one of the luma resistors (R10 to R15) are way out of tollerence. My only other suggestion would be to replace R11 with a 100K potentiometer and see if that can help. I will try and duplicate the problem. I tried this mod on two different 7800s, 2 different monitors and 3 different TVs without seing any artifacting. Differerent monitors / TVs seem to display brighter than others and the brightness and contrast may need to be adjusted.

Edited July 22, 2008 by puppetmark

[Almost Rice]

My only other suggestion would be to replace R11 with a 100K potentiometer and see if that can help.

 

Funny you should mention that.

 

I was going to just change R11 to a 47K resistor, but Metalguy66 just gave me 2 100K pots. instead. So, I was put on a perf board and I copied the same video circuit on this board, but with the input connections all one side and output on the other. He also put a capacitor on the audio pot. For the 2nd pot., I used your audio circuit instead of mine. I still had the halo problem. I found it to be a fine dust on the TV screen. The halo is still there on the Commodore 1702, but much more tolerable. I should have measured the pot, but I already closed it. I will get it next time I adjust the R11 value for the Commodore monitor.

 

So I got to enjoy a clear game of Robotron last night.

 

I think it cleaned up real well

The board is attached by the ground, +5V, and video signal connections at the RF. The top is now the video circuit and the 2 pots below and I believe that is a .01 uF cap. at the bottom. Red wires are audio in and out. Tan is POKEY sound. Browns are to R11.

[Phantom]

OK since I am all thumbs and have been banned by the State of NJ

to ever again attempt to use a soldering iron! I cant do this.

So if anyone is in NJ/PA/CT/NY/DE or NE in general where I can ship this up and back reasonably cheap, would someone mod my 7800 for me? I could offer trade or a fee. LMK if so and what you would want in return. I am told this is cheap in parts and quick to do but again I suck at soldering or any of this technical stuff.

So please LMK if anyone is interested and see my FS/FT thread if you want to get a trade for it which I would prefer as money is always tight for me and I could ship the trade with my console to you.

This is a want of mine for sometime now...

so hopefully someone can do this for me?

Please PM me if so.

Thanks -Ant

Edited July 23, 2008 by Phantom

[puppetmark]

My only other suggestion would be to replace R11 with a 100K potentiometer and see if that can help.

 

Funny you should mention that.

 

I was going to just change R11 to a 47K resistor, but Metalguy66 just gave me 2 100K pots. instead. So, I was put on a perf board and I copied the same video circuit on this board, but with the input connections all one side and output on the other. He also put a capacitor on the audio pot. For the 2nd pot., I used your audio circuit instead of mine. I still had the halo problem. I found it to be a fine dust on the TV screen. The halo is still there on the Commodore 1702, but much more tolerable. I should have measured the pot, but I already closed it. I will get it next time I adjust the R11 value for the Commodore monitor.

 

So I got to enjoy a clear game of Robotron last night.

 

I think it cleaned up real well

The board is attached by the ground, +5V, and video signal connections at the RF. The top is now the video circuit and the 2 pots below and I believe that is a .01 uF cap. at the bottom. Red wires are audio in and out. Tan is POKEY sound. Browns are to R11.

 

Nice job! I will take a closer look at the luma line R11 is attached too. I guess it could be creeping into the color signal. Maybe an adjustable pot is the answer. Maybe there is a better value that will work with a wide range of monitors / TVs. Anyway, I like what you did.

Edited July 23, 2008 by puppetmark

[Underball]

So replacing R11 with a 100k potentiometer and adjusting it will remove halos/ghosting?

 

Take a look at the track on Pole Position II and tell me if you still get the hard ghosting there. It's not terrible, but it's definitely noticeable.

[puppetmark]

So replacing R11 with a 100k potentiometer and adjusting it will remove halos/ghosting?

 

Take a look at the track on Pole Position II and tell me if you still get the hard ghosting there. It's not terrible, but it's definitely noticeable.

 

I don't know yet, maybe. I need to look into it further. It could be one of the other luma lines also. The B&W part of a video signal should not touch the color section but it sure seems like it is, so I think its not the mod that is at fault but the way the color and luma signals are combined in the 7800. I haven't noticed the problem as much as some others on this thread but maybe my eyes aren't as good.

[Almost Rice]

So replacing R11 with a 100k potentiometer and adjusting it will remove halos/ghosting?

 

Take a look at the track on Pole Position II and tell me if you still get the hard ghosting there. It's not terrible, but it's definitely noticeable.

 

Mine looks good, but it did not remove all of the halo. I had to clean my TV screen to get that. Give you screen a good wipe to make sure there is no dust.

[ApolloBoy]

Hate to bump an old topic, but I managed to get around to fixing my mod recently. I've taken the video circuit from the expansion port and soldered it to the video pin from the RF modulator. There's been no difference at all and now I'm looking at replacing R11 with a 100K pot as puppetmark suggested. Puppetmark, have you been able to duplicate my problem? I'm just hoping that I can get this fixed somehow...

[Math You]

*deleted*

Edited September 17, 2008 by Math You

[pepax]

Bear in mind that the composite signal uses the French SECAM system so you'll need a multi-standard TV if composite is your only option. The RGB signal should work with PAL or SECAM tv's.

Fortunately I'm not stuck with the composite video. I didn't even realize it was there. What I had in mind was a composite video mod of the stock PAL machine.

The RGB video is nice....... on a classic CRT TV. For some reason, it's a lot worse on my LCD with a TV tuner.

[mimo]

Bear in mind that the composite signal uses the French SECAM system so you'll need a multi-standard TV if composite is your only option. The RGB signal should work with PAL or SECAM tv's.

Fortunately I'm not stuck with the composite video. I didn't even realize it was there. What I had in mind was a composite video mod of the stock PAL machine.

The RGB video is nice....... on a classic CRT TV. For some reason, it's a lot worse on my LCD with a TV tuner.

Just found that out on my SECAM Colecovision, it really does not like my LCD tv despite the spec for the TV stating that it accepts SECAM and RGB (and a lot of other stuff)

Long live the CRT television

[puppetmark]

Hate to bump an old topic, but I managed to get around to fixing my mod recently. I've taken the video circuit from the expansion port and soldered it to the video pin from the RF modulator. There's been no difference at all and now I'm looking at replacing R11 with a 100K pot as puppetmark suggested. Puppetmark, have you been able to duplicate my problem? I'm just hoping that I can get this fixed somehow...

 

I haven't been able to duplicate the problem. I tried once without success, then I got busy with work. I will try again in the next few of days. I think the pots are the best option.