Going from composite mod to s-video mod

[tajume80]

I recently modded my ntsc 7800 to composite. I wasn't pleased with the results (it seems that the mod I bought via eBay was really bad, or I'm just spoiled by RGB ).

 

I just bought a s-video mod, and now it seems that I have to solder back the missing resistors I took off the motherboard. The thing is that I don't have the parts anymore.

 

So the question is: can anyone help me and tell me what resistors I need (the parts I need are marked in the picture)ohms etc. (I took the picture from the instructions of the composite mod)

Edited February 18, 2019 by tajume80

[+-^CrossBow^-]

Which s-video mod do you have? Because the two I use only attach to the resistor ladder just below the ones you have marked and so they could essentially remain off the board. The switch isn't needed at all for the s-video mods I use either. Unless you got the LHE mod? That would likely still require all of these components and the switch changed to be the TIA colorburst kill switch.

 

The cap is a .1uf poly. Standard stuff the one next to it is the same exact type. I would have to research the value of the resistor you marked on the left side. But the one on the right of the audio adjust coil is 18k. That you will need for proper Tia and Pokey audio balance on the volume.

[tajume80]

I bought the Magic Knight version.

[+-^CrossBow^-]

Ah....Excellent! No...I don't believe you need to put that upper resistor back in. But you do need to replace the small poly cap and the R6 resistor with an 18K 1/4watt. I keep them on hand because I've reversed several LHE and other composite mods on 7800 to bring them back to stock for UAV and Magic Knight kit installs.

[tajume80]

Ah....Excellent! No...I don't believe you need to put that upper resistor back in. But you do need to replace the small poly cap and the R6 resistor with an 18K 1/4watt. I keep them on hand because I've reversed several LHE and other composite mods on 7800 to bring them back to stock for UAV and Magic Knight kit installs.

Great! Thanks for the info!

 

Just to be sure (I'm quite new to modding, and in Atari equipment in general) in the picture below I've crossed out things I don't need to replace, if I understood correctly. So now I need 18K 1/4 watt and the poly cap.

[+-^CrossBow^-]

You have the resistors backwards. The one you have with an X is the one I was advising you replace. But...since you are using the magic knight board, you don't have to replace that since you tap the audio from the south end of those resistors. Basically you are bypassing them at that point if memory serves.

 

But having said that, Magic Knight's resistor values on his boards on the audio input lines are incorrect. I've manually changed out the resistor coming off R5 (Green/Red wire I think) to 18k on my actual Magic Knight PCBs that I have and when I populate the bare PCBs I received from him, I corrected it on those as well.

 

I will double check all of this tonight if I'm able and report back.

Edited February 19, 2019 by -^Cro§Bow^-

[tajume80]

Ok! I was suspecting that I've must understood some part wrong. I understood that the 'pokey audio' part under the channel switcher must be replaced.

 

But anyway, I modified the picture and I hope that I understood correctly this time

Edited February 19, 2019 by tajume80

[+-^CrossBow^-]

No..like this..

 

[tajume80]

No..like this..

 

corrected.jpg

Ok, now I get it! Thanks!

 

It seems that I got mixed up when coming to resistors and capacitors...all new stuff to me

[tajume80]

I just bought the 18k 1/4 watt resistor.

 

Another question: what is the correct voltage for the .1uf? 50V or 100V? Or something else?

[+-^CrossBow^-]

That is only for audio so anything over 16v is fine. I believe I use .1uf 16v on those poly caps that I have in stock.

[tajume80]

That is only for audio so anything over 16v is fine. I believe I use .1uf 16v on those poly caps that I have in stock.

Great! Thanks!

[tajume80]

I'm just installing the mod to a ntsc model. Do I need to solder the rf box back to the motherboard?

[+-^CrossBow^-]

Not if you don't plan to use RF any more no.

[tajume80]

Not if you don't plan to use RF any more no.

Ok, good to know.

 

I'm having a problem with the mod at the moment. I only get wildly scrolling black & white picture out of the mod. That's why I was wondering about the rf: "does it need it to sync the picture" etc.

[+-^CrossBow^-]

You need to adjust the Luma pot to get it dialed in. The MK boards I recently sold that I populated, I already adjusted to my AV setup here so that hopefully the new owners don't have to adjust it as much.

 

You will also get this result if you have the chroma and luma backwards. And if you don't have grounds on everything. Keep in mind the MK board doesn't include ground attachments so you have to do that on your own to ground points along the PCB.

 

NM the install guide you are in Finland so it won't do you much good.

Magic_Knight_NTSC_Installation_A7800.pdf

Edited March 7, 2019 by -^Cro§Bow^-

[tajume80]

You need to adjust the Luma pot to get it dialed in. The MK boards I recently sold that I populated, I already adjusted to my AV setup here so that hopefully the new owners don't have to adjust it as much.

 

You will also get this result if you have the chroma and luma backwards. And if you don't have grounds on everything. Keep in mind the MK board doesn't include ground attachments so you have to do that on your own to ground points along the PCB.

 

NM the install guide you are in Finland so it won't do you much good.

Thank you very much!

 

Your manual helped a lot and I took the +5V from different spot, and that helped! The picture quality is excellent, especially when compared to composite. I tried the s-video mod with Commodore 1084S and with 65" oled tv via framemaister. Both 2600 and 7800 games looked awesome!