the_crayon_king Posted January 29, 2017 Share Posted January 29, 2017 (edited) So I am trying to make a definitive way of dealing with the N64's lack of csync on certain NS1 revisions. What I think I know so far: My NUS encoder is putting out 3.36v I want to buffer the sync through a THS7374 which has a 300mv level shift (on top of the 6db [2x] gain. CS75 should be -286.00mV (I think) I should be shooting for 600mv coming out of the 7374 which will be divided by resistors to 300mv That means I need the input sync to be 150mv (300mv/2=150mv[level shift])150mv(sync)+150mv(shift)=300x2(6db gain)=600mv That would mean I'd need a voltage divider at the input. Right now I have 1.6k in series with 75ohm to ground Not sure how correct any of this stuff is. Every time I think I know whats up I miss something so let me know pls I also wonder if you could feed the TTL sync from the NUS chip directly into the sync for your TV. Visual: Edited January 29, 2017 by the_crayon_king Quote Link to comment Share on other sites More sharing options...
the_crayon_king Posted January 29, 2017 Author Share Posted January 29, 2017 So I found a N64 laying around that was already RGB modified but lacking the C-sync components described below. Anyway passing un-buffered C-sync direct from the NUS chip worked fine; dunno why I have never heard of anyone doing it before. It looks like the missing components should buffer 3.3v C-sync down to 2.3V. IDK if its right but refer to: http://i.imgur.com/WTMtHfg.png and http://tinyurl.com/zrlj2bl TTL sync's high level needs to be 2v-5v; 2.3v is a narrow margin. I wonder if that is why N64's native C-sync is known to be wonky. I would guess that there is 75ohms to ground on the sync end of the scart cable but without series resistor there is no voltage lost. I think that issues may arise over longer cables or perhaps there may be some impedance issues but it looked fine on my TV. For reference I am using retro_console_accessories C# scart cable. This stuff is all for a new N64 RGB board revision I have been working on: https://easyeda.com/hotdog6394/N64_THS_7374-h30K6sOa8 As with all my boards feel free to print and use for personal use, mod services, whatever; just not resale, Print at 0.6-0.8 Ill have to make another revision for hand soldering this specific board is for machine assembly but should be possible by hand. Quote Link to comment Share on other sites More sharing options...
the_crayon_king Posted February 6, 2017 Author Share Posted February 6, 2017 (edited) I built the above circuit and got about a 150mv shift as the sync pulse (which is not what I expected but it did work on my setup). Sync direct out of the NUS encoder looks like a 3v p-p shift and all the references I can find say sync should be a -0.3v shift. The top on this next picture is the Typical TTL to Non TTL solution but it isn't the same as CS#75 which is what I am shooting for. I am trying to find more info on sync and what it needs to be but this is a good enough approximation for now. I did notice a bunch of extra noise on the Csync waveform after buffering with the THS7374 I suspect it might be line noise that is much more aparent looking at the buffered (smaller) signal vs the TTL (unbuffered/larger) signal. Notes: The 75 ohm resistor on the topmost would be the termination resistor for the TTL>NON-TTL The 75 on the bottom-right would also be a termination resistor. The other 75ohm on the bottom left is just for dividing. So this should be a better solution http://tinyurl.com/h7pa4ow: Edited February 6, 2017 by the_crayon_king Quote Link to comment Share on other sites More sharing options...
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