Longhorn Engineer

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.

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!

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.

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.

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

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.

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

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.

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.

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

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

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

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

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

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

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.

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).

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.

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

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

Let me know if you have any issues.

Same with the 7800 mod.

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.

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 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. 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. 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.