N64 RGB Mod - Poor quality image

Discussion in 'Modding and Hacking - Consoles and Electronics' started by fathertime, Jul 16, 2011.

  1. marqs

    marqs Member

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    Notice that using Csync instead of cvideo results in the picture position shifted a bit left. Some TVs (CRT & flat) have the option to center the picture, some don't. I think one easy way to obtain Csync would be to just disconnect the subcarrier input (pin 8) from ENC-NUS, which would result in sync only on Cvideo line. Haven't tested that though.
     
  2. Bad_Ad84

    Bad_Ad84 The Tick

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    sync splitter using cvideo doesnt help, so that might not work.

    luma has no shifted picture on anything ive tested it on
     
  3. hugocraft

    hugocraft Rising Member

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    Dumb question but the part above I would connect PIN7 to PIN9 with just one 75ohm resistor and cut cut the composite video sync trace under PIN9?

    Asking because I don't get how you connect those 2 pins in series if just using 1 resistor to connect them.
     
    Last edited: Jan 24, 2013
  4. Bad_Ad84

    Bad_Ad84 The Tick

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    1 end of the resistor to pin 7 and the other to pin 9.

    I dont know why he has said in series, if you are linking pin 7 to 9 - there is no series or parallel, its just linking them together.
     
  5. hugocraft

    hugocraft Rising Member

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    okay thanks, I was just double checking!

    I got theTHS7314 in so just need to get (4) 75ohm Resistors (1) 0.1uF Capacitor and start moding! mmmonkey says he uses Kynar wire but after googling around I think its safe to just use ethernet wiring since I have a ton of it, its small, and I can easily color code it. Good or bad idea?
     
  6. Bad_Ad84

    Bad_Ad84 The Tick

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    See no issues with that
     
  7. hugocraft

    hugocraft Rising Member

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    I got the .1uf cap but at radio shack the closest I could find to a 75ohm resistor was a 68ohm 1/2watt. I was thinking 1/4w is what is called for but will the 68ohm 1/2watt ones work okay?
     
  8. Bad_Ad84

    Bad_Ad84 The Tick

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    I dont even use a resistor, I just link them.

    Edit:

    For clarity, I am talking about the pin 7 - 9 part. You do require the resistors from the amp on the RGB lines.
     
    Last edited: Jan 29, 2013
  9. hugocraft

    hugocraft Rising Member

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  10. Bad_Ad84

    Bad_Ad84 The Tick

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    You need the 3 off the amp, the one between 7 and 9 I dont believe is even required - but thats what the op did. I never used a resistor and its worked fine.
     
  11. Calpis

    Calpis Champion of the Forum

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    If you don't put in a series output resistor the signal level is twice what it should be (so you should use a unity gain amplifier instead) and there is no source termination. Source termination is important for damping signal reflections that come from inevitable impedance mismatch.
     
  12. Bad_Ad84

    Bad_Ad84 The Tick

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    Which are you talking about? Luma?

    On a NTSC console luma is directly output to the TV from the N64 with nothing in the cable. a PAL N64 has a resistor to ground (which is in the PAL rgb cable anyway on the composite/sync line).

    RGB lines I said need resistors.

    Though I use the PAL cable (with 75ohm resistor to ground on composite video, which with this mod is actually luma for sync) on NTSC consoles too and that works fine. Like I said, I dont think the one in series is even required for luma
     
    Last edited: Jan 29, 2013
  13. Calpis

    Calpis Champion of the Forum

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    (AFAIK) PAL cables have shunt resistors, not series, so the voltage is still twice what it should be, but now the amplifier has twice the loading. THS amplifiers have gain, so you really shouldn't use them that way. They are designed for bog-standard series source/parallel load termination which (AFAIK) PAL cables don't provide. (AFAIK) PAL SNES are designed specifically for the cable which is why the RGB signals have a special buffer circuit instead of directly using the amplified RGB output from the RGB encoder. (It was another form of lockout.)
     
    Last edited: Jan 29, 2013
  14. Bad_Ad84

    Bad_Ad84 The Tick

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    I think we are talking about different things....

    Luma (the pin 7 to 9 mod) doesnt go via the THS at all. It goes straight down the composite video line and is used for sync - which is the one I said doesnt need the resistor (ntsc consoles have luma straight to the TV, nothing in the cable - so its "as designed").

    The RGB lines, I said need resistors in series, but also to ground at the cable end - else the image is over saturated with just the ones in series.

    I dont know what you are replying to, as its not something I have said... the only resistor I said he didnt need was on the connecting luma to composite video (after cutting the trace to composite video).


    Edit:

    Despite this being a different amp, with the resistor in series after the amp and the resistors to ground in the PAL cable, you end up with something like this:

    [​IMG]

    But with just the 3 RGB lines
     
    Last edited: Jan 29, 2013
  15. Calpis

    Calpis Champion of the Forum

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    He said he could only find 68 ohm series termination resistors, you replied to that post saying you don't use them. He replied it's probably OK to use none of them. So not paying close attention to the thread I dunno what to think...

    Anyways for the N64 mod it's wrong to have shunt 75 ohm resistors to GND anywhere. If you need them to bring the level down... Something isn't right.

    Edit: even the mmmonkey site says to use the GC SCART cable (which shouldn't have the shunt resistors).
     
    Last edited: Jan 29, 2013
  16. Bad_Ad84

    Bad_Ad84 The Tick

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    Was just the Luma one (pin 7 to 9) I said wasnt needed, I said the other 3 from the amp are required.


    Edit:

    Reading back I can see why you read it like that, but the reply where I said I didnt use a resistor was while we were discussing the pin 7 -9 part (they were quick replies back and forth). But reading it after the fact, I can see why it looks like that.

    I will edit that part for clarity and google/archival sake.


    Edit2:

    Does have caps though, so that might be why. But to be fair, it wasnt something I mentioned in this thread initially - just the pin 7 -9 thing.
     
    Last edited: Jan 29, 2013
  17. Calpis

    Calpis Champion of the Forum

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    I realize this is irrelevant at this point but

    This diagram reinforces what I said. The 75 R to GND you're referring to is actually the TV's termination resistor on the far side of the transmission line (coax cable). There is no 75 R to GND at the jack.
    The PAL SNES is the only device with a 75 R at the jack because it purposefully uses a screwed up termination topology. Hopefully this clears it up:

    [​IMG]
     
    Last edited: Jan 29, 2013
  18. Bad_Ad84

    Bad_Ad84 The Tick

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    Well, like you said - something obviously isnt correct with your first diagram - as the image is not correct, its over saturated when done like that.

    I will test a GC cable (the difference being no shunt resistors, but caps in series instead) and see if that improves things.

    I do appreciate your explanation though - video and analog is confusing as an amateur.

    Edit:

    To be fair, I now own a scope - so I could just check it.
     
    Last edited: Jan 29, 2013
  19. hugocraft

    hugocraft Rising Member

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    I'm using an NTSC n64 and the RGB mod is done and picture looks great. I used 68 ohm resistors coming out of the ths chip and another resistor to connect pins 7 and 9 after cutting the trace from 7

    Not the prettiest mod but I'm sure I can do a much better job on the next one. Also I have sticky clear tape on both sides of the mod covering it all and I cut away some the metal shielding since the resistors stick out to that area on the edge. You can't see where I cut the trace since its under a wire.

    View attachment 5556

    I got the N64 w/grey controller off craigslist so with parts I have $30 invested in an RGB n64 w/controller! YAY!
     
    Last edited: Jan 29, 2013
  20. IceMaN30

    IceMaN30 Member

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    First off his thread has helped me immensely in getting my NTSC N64 rgb mod working. Thanks to all of the contributors!!

    Second I am a little confused on a couple of things. So far I have an NUS-CPU-04 with the THS7314 amp installed and it looks much better than composite on my Samsung LCD. The only problem is that I'm getting a moire pattern on certain colors/games. It looks terrible in StarFox but not so bad in Mario Kart. Also I'm getting some dancing lines (sorry for the poor choice of words, I'd be happy to post some pics) along the edges text or colors in general. Since I have a Sammy TV I understand that I should get the Sync from Luma and not composite video as it is currently set up. I am a little confused on one thing though. On some posts it says in order to get Luma Sync I neeed to cut the trace on 7 and others the trace on 9.

    I understand it that trace 9 needs to be cut but I just wanted to double check before I start hacking away.

    Thanks again!
     

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