[Atari A/V mod update]

Got my replacement board, and soldered it together yesterday... Same problem: black and white video on the 7800, and either scrambled or black screen on the 2600 side. I want to say that Joe Martowicz has been tremendously helpful in troubleshooting this with me. Don't know the relationship between Martowicz and LHE, but I still believe it's a great design. Hoping I can get it fully functional soon!

 

I'm tempted to modify my original 1984 Warner Communications model, but I don't want to start clipping things just yet. I did completely remove the RF modulator box, so I'm hoping that doesn't affect anything.

 

 

Can you post some high resolution shots of the connections you made?

 

I just sell PCBs to Joe but I am the one that designed the mod.

[Atari A/V mod update]

2. With all 7800 games, I get no color at all. Just black and white images:

 

 

 

I have no idea how to troubleshoot this one. By the way, the same symptoms happen with both S-Video and Composite outputs.

 

Any thoughts at all would be greatly appreciated.

 

EDIT: I have another 2600-related issue. I popped in Asteroids and the characters seem to jump around...almost like it's a vertical-hold issue, but I've got it hooked up to an HDTV. Thoughts?

 

I had the black and white issue when I got mine as well. I ended up having to touch up the soldering on one of the chips per LH's suggestion. It was the really tiny chip. I needed to reflow the solder. With my lousy hand steadiness, it was quite the chore.

 

Hi all,

 

I just purchased and installed my LHE video mod for the Atari 7800. Picture in the 7800 mode is clear albeit in black and white over S-video and composite. 2600 mode is scrambled and also in black and white. I've tried this on both my Westinghouse W4207 and a Dell FPD on both channels. I've done a pretty rigorous search on how to resolve this issue, but these posts are the closest I've come.

 

I've checked all my connections—especially to pin 9 (chroma)—and even replaced a few wires. In 2600 mode, I adjusted the lower potentiometer and this helped the V-Hold, but the image is still off-center and black and white.

 

Can anyone help me with this issue? I'm dying to play my ProSys in full color!

 

Thanks!

 

Sounds like the tiny chip in the bottom right corner is not working correctly. That chip passes the chroma signal.

 

Thanks LHE! I found that post several pages back, and I do believe that's the problem. Since I purchased mine from electronicsentimentalities, I e-mailed him, and he's going to replace the board.

 

I did attempt to reflow the solder on the little guy, but it just wasn't happening.

 

Cheers to a fantastic design! Even in b/w it is remarkably crisp and sharp!

 

No problem!

[Atari A/V mod update]

2. With all 7800 games, I get no color at all. Just black and white images:

 

 

 

I have no idea how to troubleshoot this one. By the way, the same symptoms happen with both S-Video and Composite outputs.

 

Any thoughts at all would be greatly appreciated.

 

EDIT: I have another 2600-related issue. I popped in Asteroids and the characters seem to jump around...almost like it's a vertical-hold issue, but I've got it hooked up to an HDTV. Thoughts?

 

I had the black and white issue when I got mine as well. I ended up having to touch up the soldering on one of the chips per LH's suggestion. It was the really tiny chip. I needed to reflow the solder. With my lousy hand steadiness, it was quite the chore.

 

Hi all,

 

I just purchased and installed my LHE video mod for the Atari 7800. Picture in the 7800 mode is clear albeit in black and white over S-video and composite. 2600 mode is scrambled and also in black and white. I've tried this on both my Westinghouse W4207 and a Dell FPD on both channels. I've done a pretty rigorous search on how to resolve this issue, but these posts are the closest I've come.

 

I've checked all my connections—especially to pin 9 (chroma)—and even replaced a few wires. In 2600 mode, I adjusted the lower potentiometer and this helped the V-Hold, but the image is still off-center and black and white.

 

Can anyone help me with this issue? I'm dying to play my ProSys in full color!

 

Thanks!

 

Sounds like the tiny chip in the bottom right corner is not working correctly. That chip passes the chroma signal.

[Current Video Mods (2600)]

Don't order from the LHE directly, i placed my order last November and i'm still waiting!

 

Just to update this, i have since received the mod so hopefully Longhorn is now uptodate.

Awesome picture quality on S-video btw

 

I am but I am not taking direct orders right now. I am selling bulk PCBs to people that want to sell mods however. I want to get back to selling them but I do not have time to assemble all those orders.

[Sega Genesis is overheating]

The fact that it still works until hot leads me to think it's something that simple. Possibly even a cracked solder joint. While I'm sure it can happen, I've never seen a failed Sega Genesis or SMS, but I have seen owners fail their Sega.

 

Wouldn't surprise me if a connection on the cart slot got cracked.

[Atari A/V mod update]

It is all designed and ready to go but I need to test it and finish up the PCB.

 

If you get me the schematic I'll give it a go, and let you know how it works. Nice to have 3rd party verification?

 

Will once I make sure it doesnt blow up TVs or 5200's

 

You have something against fireworks?

 

I don't mind but I am sure people don't want there houses going down in a blaze of Atari glory.

[Atari A/V mod update]

It is all designed and ready to go but I need to test it and finish up the PCB.

 

If you get me the schematic I'll give it a go, and let you know how it works. Nice to have 3rd party verification?

 

Will once I make sure it doesnt blow up TVs or 5200's

[Atari A/V mod update]

At the risk of being flamed are there still plans for an updated 5200 A/V mod?

 

Why would any one flame you?

 

And Yes there is a 5200 design but I am more focused on getting every one who has already ordered a mod out the door before even thinking about working on a new design. It is all designed and ready to go but I need to test it and finish up the PCB.

[Atari A/V mod update]

DigiKey has them in-stock. 1500 exactly, so maybe they recently got a reel of 2500 and sold 1000 of them to a customer.

I just ordered a small quantity of them...I'll repost when I know if it goes through or not. I wonder where they got 2500 of them?

 

In December Fairchild (manufacture of the FMS6400) placed the FMS6400 on "last orders" then moved it to discontinued. I bet the 1500 chips where from an order then.

[Atari A/V mod update]

DigiKey has them in-stock. 1500 exactly, so maybe they recently got a reel of 2500 and sold 1000 of them to a customer.

 

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=96763678&uq=634339569467237059

 

Should last quite awhile.

[Atari A/V mod update]

Quick question... Parker uses 22AWG wire in this mod, is there any reason that 24AWG wouldn't work?

 

22AWG is used cause I can get 10 conductor wire (multi colors) for really cheap. 24AWG should be fine.

 

Parker

[Atari A/V mod update]

I would see what video options your TV has and try tweaking them. Or try adding the RF shielding back on. Your install looks correct.

 

Parker

[Let's design a new video mod]

The 2N3904 adds about a 22ns delay in the signal. Try buffering the COL signal as well.

 

Parker

[Let's design a new video mod]

The 10uF cap near the FMS6400 chip needs to be ceramic. Electrolytic caps won't be fast enough to do the job.

[Atari A/V mod update]

Did you twist the red wire (ground) and the composite wire (yellow) together? Also could you email me some photos of the install along with with the lines on the TV? I am assuming your using a stock Atari power supply and a good composite cable.

 

Parker

[Let's design a new video mod]

The 100uF cap was specified in the original CD4050 mod (which dates back to the mid-90's) and its purpose was never questioned.

 

Also, my purpose with this mod is to make something simple, possible to build by hand, but still with very high quality output.

 

So maybe it will be possible to produce a mod that uses 3x the parts, costs $100 and gives almost unnoticeably better output, but I'd guess you'd be one of the few to buy one.

 

I used the 100uF cap because that is the normal capacitor rating for your power rail in something the size of the video mod. Its convention if anything. You can never know what kind of power that 7805 that is 30 years old is putting out.

[Let's design a new video mod]

I discovered that I had a bad connection somewhere in my build. Perhaps more than one. But now I now have a very excellent s-video output. Colors are great. There's no bleeding whatsoever. The only problems I see are a slight vertical banding and composite is bit darker than s-video. I've not installed the pots yet, but I'll play with those soon.

 

Check to see what the vertical banding is in by disconnecting the Chroma or Luma. Vertical banding is usually caused by a over amped chroma line or the luma not being buffered (lack of 2n3904 could cause this).

[Atari A/V mod update]

Ugh broke the shell of my Jr. drilling with the Forstner bits.

 

You have to let the bit do the cutting and make sure to go evenly through the plastic. Even with specially purposed drill bits the plastic used on Ataris is very brittle and even more so that they are several decades old now.

 

Since I have switched to Forstner bits I have yet to crack an Atari case. Best part about them is that they don't chip the plastic on exit either.

[Let's design a new video mod]

I don't know if this is a factor or not, but on some 2600s the longhorn mod seems to have an overly bright display. My 4 switcher is also one of them.

 

That was before I switched to the higher resistor values for the DAC resistor ladder. It has been fixed in the newer versions of the board.

 

Parker

[Atari A/V mod update]

Also finished a mod for a friend on a 4 switch, it has the color bleed problem mentioned long ago, was that ever corrected or is it still out there. If I remember correctly it was a delay with the luma signal?

 

Thanks in advance.

 

The mod doesn't completely eliminate the bleed. batari on the other thread passed the color through the 74HC4050 and got it to work. It is never going to be perfect due to the nature of composite and s-video signals (color phase) but batari got pretty close.

 

Parker

[Atari A/V mod update]

Thank you.

 

Let me know if you have any issues.

[Atari A/V mod update]

I'm thinking only Parker can answer this question, and he probably won't since he probably hates my guts, but I'll ask anyway.

 

On the 2600 mod with the new FMS64xx chip Parker says to not install 3 of the 75Ohm resisters. Is this the case for the 7800 board as well, or do I assemble it just as instructed?

 

Same with the 7800 mod.

[Let's design a new video mod]

The FMS6400 requires a 75ohm input impedance and a .1uf ceramic capacitor. If you look at the schematic theres a 75 ohm in series and one pulling it to ground. This sets up the input impedance. The 2n3904 does add gain to the luma signal.

I am looking at the datasheet now, and there are no resistors at input, only the 0.1 uF caps, and I see nothing at all about required input impedance. At output, there is only the series resistor, and the resistor to ground appears to be after a 75 ohm coaxial cable (which I assume means an impedance matching resistor in the television itself.) It's not clear from the diagram alone, but looking in other datasheets for other video chips and other video circuits, this seems to be correct.

 

Read the application information on the datasheet. The Luma input needs to be driven by a low impedance source or a 75ohm terminated line. The 2n3904 causes a really high impedance on the luma line so the 75ohm resistors where necessary in this case.

 

If you remove the 2n3904 from the design as is it will produce a noticeably darker image on the TV. Its mainly for increasing the current load for the luma. The DAC portion pretty much sucks all the current out of the luma signal. If you got a CD4050 that could source more current you might be able to do away with it.

[Let's design a new video mod]

LHE didn't follow the CD4050 verbatim. He changed the size of resistors in the D/A resistor ladder at LUM0-2, which I think aren't critical, but the resistors at LUM1 needs to be twice the value of LUM0, and LUM2 is 2x LUM1. The size seems to only affect output current, not voltage. For now, I'll keep these as they are and experiment with sizes if the output current matters.

 

The original values in that mod are to low and close together. The top 3 luma levels blend together so the contrast of your image goes down

 

There are some design decisions that I don't understand about the the LHE mod. The CD4050 mod has two transistors and his has one. He used the emitter-follower transistor for Luma but used the same method on the six-switch schematic of combining COL and BLK for Chroma, then he added the 75 ohm resistor on both with series capacitors. One problem here is the Luma will have correct 75 ohm impedance due to the transistor but Chroma will not (due to the 600 and 1k resistors.) It's possible that his video chip doesn't care about the input impedance and only the series caps would be needed. If this is the case, and I suspect it is, there is no need for the transistor at Luma, or the various resistors around it.

 

The FMS6400 requires a 75ohm input impedance and a .1uf ceramic capacitor. If you look at the schematic theres a 75 ohm in series and one pulling it to ground. This sets up the input impedance. The 2n3904 does add gain to the luma signal.

 

Another thing I don't understand is why he buffered BLK, but still used the same method of combining the signals as the 6-switch. One issue is that TIA outputs are open-drain but the CD4050 is not. This could mean that you can't just copy the method of combining BLK and COL from the six-switch schematics, as when BLK is high, it will tend to pull up the signal with a CD4050 but the TIA would not. So either a diode should have been added here (similar to the one on the buffered Sync signal) or BLK should not have been buffered.

 

It is buffered to attempt to keep it more in synced with the luma signal. This signal is basically means "off screen" when the electron beam in a TV comes back across. Its not really needed but some TVs have a much better picture quality with it. Mainly older tube TVs.

 

Also, if everything else is buffered, you might as well buffer COL as well. I read a post where someone asked why this wasn't done, and I think LHE said it was an analog signal, but it is not - it is actually a digital signal, but delayed so it will be out of phase as the phase of the signal determines the color. I read some comments on the video mod thread about the propagation delay of the buffer being an issue, so maybe combining the BLK and COL signals first then buffering them would be the best idea. This of course would rely on fairly even propagation delay at the CD4050 which probably isn't completely accurate but probably better than not buffering at all.

 

You can't buffer the COL signal as IT IS analog. Buffers work by reading the value and propagating that through a gate. Running the COL signal through a buffer would basically be sampling the signal every 20ns or so and assigning it a high or low value depending on the voltage level of it.

 

editt// passing the COL through the buffer would probably do strange things to the phase.

[Atari A/V mod update]

Parker, been emailing you for a month so again i'm resorting to trying to contact you here. Are you getting me emails at all?

Same here. Still no product.

 

They are coming don't you worry. It took a long time to source a good number of those FMS6410 chips.