N64 RGB Mod - Poor quality image

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

  1. Bad_Ad84

    Bad_Ad84 The Tick

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    Cut 9, connect to 7
     
  2. IceMaN30

    IceMaN30 Member

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    Thanks for the conformation Bad_Ad. I proceeded to cut the trace on 9 and link it to 7 with a 100ohm resistor and now I'm getting no signal to my TV. I'm going to try to link them directly without a resistor like you mentioned earlier but I'm wondering how likely is it that my TV doesn't like the sync from luma? If linking it directly doesn't work I'll try to link c-sync to pin 9 from via of 'R16' and see how that works.
     
  3. Patrick

    Patrick Rising Member

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    I did the same mod on my french N64, but when I play US games (via Everdrive) the image shifted to the left. The same thing happens when I switch the TV mode to M-PAL or NTSC.

    Does somebody have solution for this ?
     
  4. FireAza

    FireAza Shake! Shake!

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    I'm guessing that's because NTSC games run at a lower resolution than PAL, so your N64, which outputs in PAL, is getting messed up when trying to output an NTSC source.
     
  5. ShadowZero

    ShadowZero Spirited Member

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    Does this refer to the image being dark or to the x-pattern issue?
     
  6. retronerd

    retronerd Spirited Member

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    I have done this mod but i got the net effect on my lcd tv so i cut trace 9 and bridged it to 7. i accidently cut the left audio trace. is there an alternative left audio spot so can repair the left audio line?
     
    Last edited: Sep 12, 2013
  7. retronerd

    retronerd Spirited Member

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    Nevermind, i was figuering it out:)
     
  8. robneal81

    robneal81 Site Supporter 2015

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    I'm sorry if this is a stupid question, but I'm a bit confused. I have an NTSC N64 that's RGB-modded and works perfect on my Sony PVM. I'm switching to a display that can't accept composite video as sync, so I was hoping to get csync. I tried attaching pin 18 of the VDC-NUS chip to pin 3 of the multi-out, but that didn't make a difference (I'm testing with two different cables: One that gets sync from composite video, the other that gets sync from pin 3).

    My motherboard revision is NUS-CPU-04. Is there another way to get csync directly from the console, or do I have to build a sync stripper into it?

    Thanks.
     
  9. Bad_Ad84

    Bad_Ad84 The Tick

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    If you solder it to pin 3, but do not change the cable - the cable will still be using pin 9 (composite video). You need a cable that uses pin 3 or cut pin 3 and solder the wire to that.
     
  10. robneal81

    robneal81 Site Supporter 2015

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    Solder what to pin 3?
     
  11. robneal81

    robneal81 Site Supporter 2015

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    I just want to be clear: I'm currently using an N64 that's had the R-G-B pins wired from the VDC-NUS chip, through an amp, to their proper pins on the multi-out. I use a SNES RGB cable that gets sync from the composite video pin. This setup works perfect on my Sony PVM, but I'm switching to an NEC XM29.

    My NEC XM29 is very sensitive to sync: It will NOT accept composite video as sync (for RGBs) and it even has issues with my SMS and Genesis...even though I'm using cables that get sync from the csync pin, not composite video.

    I was able to get csync from my RGB-modded SNES mini...that worked perfect and was simple: I just wired the csync pin from the S-RGB chip to pin 3 on the multi-out (and then switched RGB cables to one that gets sync from the "sync" pin (pin 3), not composite video (pin 9). I was hoping to do something similar with my N64; I had read that pin 18 from the VDC-NUS chip is csync, so I tried wiring it, but it did nothing at all.

    Is there any way I can get csync from this "NUS-CPU-04" N64? If not, I can take the composite video from pin 9, run it through an LM1881 (a sync stripper) and wire the output to pin 3...that would DEFINITELY work, but I'd really rather avoid doing it.
     
  12. robneal81

    robneal81 Site Supporter 2015

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    I'm sorry for all the posts, but it gets weirder: I have a 2nd RGB-modded N64, this one is an NUS-CPU-03. Pin 3 is unmodified, I only wired R-G-B...but if I use an RGB cable that gets sync from pin 3, it works fine on my PVM....but not the XM29.


    Could it be that this NUS-CPU-03 N64 has csync pre-wired to pin 3, but it's "dirty" sync, just like with my Genesis and SMS?


    I hope this is all making sense. Please let me know if I need to clear anything up...and thanks to anyone who can help!
     
  13. APE

    APE Site Supporter 2015

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    C-SYNC is supposed to be pure sync that is also pre-buffered, at least on the 03 models. The 04 the signal is present but the circuitry to buffer and connect it to the AV connector is missing. It shouldn't be "dirty" either.

    I just looked at a basic spec sheet of the XM29 and I'm not seeing any dedicated RGB+SYNC input or SCART, etc. How exactly are you hooking up your various consoles to it?
     
  14. robneal81

    robneal81 Site Supporter 2015

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    Console to SCART switch. SCART switch output to VGA input (which accept both VGA and RGB), via a cable I made. So far, it works perfect with the SNES Mini, RGB-modded NES, Sega Saturn (cable pulls from sync, not composite video) and Dreamcast. It's just the N64 and Genesis that are giving me trouble.

    Sync compatibility seems to be a common problem with the XM29 and I've seen people on shumps forums complain of the same issue with Genesis. It's not just the XM29, there are some switches (non-SCART) that are equally as sensitive to composite video used as sync. I can get around it with a sync stripper...but I'm hoping for an easier (and lazier) solution.
     
    Last edited: Nov 1, 2013
  15. Calpis

    Calpis Champion of the Forum

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    In practice whenever you need a RGB amplifier you'll also need a sync driver--a fourth amplifier channel (for TV level sync) or resistive network circuit (for logic level sync).

    The N64's DAC provides a logic level sync, which can only be expected to drive a modest logic load, definitely not a TV input. Your options are to stick a 680 ohm resistor in series with the DAC signal, which attenuates the signal to the desired TV level at the input, and reduces the the current the DAC must supply (4.4 mA vs 44 mA!). Without question the DAC cannot handle 44 mA, but most likely it'll also struggle with 4.4 mA. A better solution is to buffer the signal with a high-drive CMOS buffer and an impedance matched resistor network for optimal transmission. The simplest resistor network is a resistive divider of 300 ohms series, 100 ohms shunt to ground. (This will require a buffer that can source >10 mA--Ioh in the datasheet will be -10 mA or higher.)
     
    Last edited: Nov 1, 2013
  16. APE

    APE Site Supporter 2015

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    Sounds like once again we're merely getting lucky that the inputs on our displays are so tolerant of what we're feeding them.
     
  17. Calpis

    Calpis Champion of the Forum

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    When you wire the logic output directly the TV's sync detector probably doesn't care, you're just giving it a huge signal which in most cases makes its job easier as long as it's a dedicated sync input and not a video input. The DAC on the other hand won't appreciate being forced into sourcing a constant 44 mA considering that's 100+ logic loads. Plus not only is it being asked to drive such a heavy resistive load, but the coax cable itself represents a ton of capacitance and without output resistance as a buffer the capacitance is effectively shorted to the output on signal transitions. Total chip abuse.
     
  18. robneal81

    robneal81 Site Supporter 2015

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    Calpis, I very much appreciate your responses, but it went way over my head. I'm going to just assume I need to build a sync stripper into my N64...
     
  19. Calpis

    Calpis Champion of the Forum

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    A sync stripper will do nothing but give you a logic level sync, which is what you already have from the DAC. When people wire a LM1881 directly to their TV they're doing the exact same (wrong) thing.
     
  20. robneal81

    robneal81 Site Supporter 2015

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    Right, you don't just wire the LM1881, you need a small circuit: http://www.mmmonkey.co.uk/composite-sync-stripper-lm1881/

    Essentially, that's what a sync strike is...and if I route my systems through my sync strike, it works perfect through the XM29.
     

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