No colour from 32X S-video mod

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  • #26043
    Mock
    Participant

    A bit of background first… TL:DR at the end…

    It’s been a bit of a struggle getting clean signals from all my consoles into the Retrotink, my beloved Joytech AV Control Center 2 puts out some voltage over all outputs even when the source input is different, rendering it incompatible because it plays havoc with the mixed inputs on the retrotink.
    Now I’ve finally got clean inputs by removing the Joytech and having 3 separate manual unpowered switches instead – one exclusively for s-video, one for composite, and one for component.

    Another painful sacrifice to get the ‘Tink working with the cleanest picture was removing my PVM from the video chain, because it weakens the signals too much for the Retrotink, only managing to pass ugly and flaky images through. Still, these sacrifices are worth it to get clean lag-free 240p/480i handling for the big TV! 🙂

    The ultimate setup I’ve come up with is:
    Console -> Video Switch -> Retrotink 2X -> HDMI to VGA converter -> Kramer VP-720DS Scaling to 720p/1440×1080 (no lag added in VGA/DVI upscaling) -> VGA Scanline Generator -> VGA to HDMI converter -> HDMI switch -> Receiver -> TV.
    Some rough earlier tests involving the PVM mixed into the chain show only 1 frame of video lag, which can be attributed to my Vizio D50-D1. Excellent!

    ————————-

    So, I’ve encountered and worked around many flaws over the past few days to get to a working setup – however, one console is still proving to be a nightmare – my s-video modded 32X!

    I get a sharp full colour signal when I hook it up to my Kramer VP-720DS Presentation Scaler directly, which is how I currently have it setup, but the Kramer adds FIVE FRAMES of lag on S-video input (yuck!), or a cheapo amazon S-video to HDMI converter (force stretched to 16:9, yuck!).
    I get a sharp black/white picture when I hook it up to an Extron IN1508 Presentation Scaler, or the Retrotink 2X – whether directly to their inputs, or through a switch.

    The mod I’ve done is this one: http://retrotimegames.com/page12.html
    The luma signal is amplified through a transistor in the mod, but chroma is not, feeding directly from pin 3 on the 32x video encoder. I feel like if I amplified the chroma signal in the same way as luma, then it might work, this is based on the assumption that the Extron/Retrotink simply don’t have enough chroma to work with – but I don’t know enough about these things to be sure.

    I’m capable of following instructions to install a mod like this, but I don’t understand the intricacies of these signals enough to be able to make my own changes.

    TL:DR – will amplifying the chroma signal on my 32x S-video mod fix my problem of a black/white image being outputted from the Retrotink? or is there some other solution I’m not thinking of? I’d like a more-learned opinion before busting out the soldering iron again, because the mod works perfectly when the Retrotink is not involved.

    #26045
    nmalinoski
    Participant

    I get a sharp black/white picture when I hook it up to an Extron IN1508 Presentation Scaler, or the Retrotink 2X – whether directly to their inputs, or through a switch.

    Knowing that composite over S-Video is, stupidly and unfortunately, a thing, and that the IN1508 will only interpret luma from composite over S-Video, resulting in a black-and-white image, it sounds like chroma isn’t connected.

    So, if the IN1508 isn’t showing color, and your VP-720DS (Does this say whether it’s receiving CVBS or YC?) and el cheapo converter are showing color, it sounds to me like composite is being sent, not YC.

    Please post photos of your mod work so they can be inspected and compared to the instructions you linked. In the meantime, I’d doublecheck my work, particularly around where the instructions say to remove that resistor and replace it with a switch.

    #26049
    Mock
    Participant

    Been messing around a bit with the breadboard, slapping an 82ohm or 120ohm resistor (don’t have a 75) on the chroma out from pin 3 gets me colour – but it is way off on the retrotink, the Sega logo is red, if I adjust the hue control on the Kramer is MAX, the colour is almost correct, maybe just a little washed out from the slightly high resistance? However, can’t blame Kramer, I get the same result plugging in the Retrotink to the TV directly.

    Colour into the PVM is perfect under the same conditions and goes to black/white when chroma is disconnected.

    R45 is gone, but I never put in the switch. S-video for life. 🙂

    To be extra sure the PVM wasn’t seeing colour information from composite over luma, I disconnected the chroma line, and fed the s-video out from the console into an s-video-RCA adapter into the PVM on the composite input. Perfect black and white on the shared s-video/composite input 1, nothing except some occasional flickery lines on input 2, which is composite only.

    Something odd perhaps: So I can now get horrible colour on Retrotink on the Y/C input, but if I cycle through all the inputs back to Y/C, colour is lost again until I restart the console.

    edit: Actually the colour shift is not consistent, every time I power on the Genesis a new shift appears. There are 3 far, one where I set hue to 32, another where hue is 80, and the aforementioned one where the max value is needed. Gotta get this chroma signal in spec I think.

    edit 2: Another thing is note is that the picture from the retrotink LOOKS like composite with lots of colour bleed and interference when I do this, while the same output directly into the Kramer is super sharp. Hmm.

    #26053
    Mock
    Participant

    Exact same output, top into Kramer directly, bottom to Retrotink.

    edit: images removed

    Okay, turns out there was a bootleg crossed S-video cable I was using in the chain, this is now gone, so I now have a sharp image with the colour shifts.

    Edit 2: This is where I’m at now. Re-built the circuit a bit nicer than before, no resistor on Chroma and now I can reliably get colour-shifted video thru the ‘tink. Here’s the shift…

    SMPTE test colours in 240p test suite. S-video fed through the PVM first, then out to the video chain. I put back the Joytech switch back in the S-video path because the cheap manual switch was dumping S-video signal out of all the empty composite holes – as long as the Joytech only has S-video cords and audio plugged in it actually does work.

    PVM displays correctly, then the retrotink has a spasm with it. Tried changing the Kramer input from RGB to YUV but that is not the fix either.

    #26071
    James-F
    Participant

    The Sega Genesis and 32x use a simplistic resonance bandpass filter around 3.58MHz for Chroma, which changes phase and far from proper BT.470 specification.
    Some NTSC decoders can’t lock to that grossly out-of-spec terrible chroma signal and get hue shifts or no color at all.
    Sony’s NTSC decoders in their TVs/PVM/BVM are more tolerable for this bad chroma signal, but other equipment may not be.

    Please consider using HD Retrovision cables if you are in the US or the new console Component cables from retrogamingcables.co.uk if you are from Europe.

    https://www.hdretrovision.com/genesis
    https://www.retrogamingcables.co.uk/Component-YPbPr-240p

    #26075
    Mock
    Participant

    Thanks for the definitive explanation, when I was toying with the idea of amplifying colour I stumbled across some info detailing that the phase could be wrong. Very nearly ordered a Kramer VM-9YC so I could fiddle around with C-phase, but if I’m going to spend $80 (CAD) on something the Retrovision cables are a much safer bet.

    I would have pulled the trigger already if they were in stock. 🙂

    Will the HD Retrovision cable require R45 (composite) to be reconnected for sync, or any other reason?

    edit: Sorry, I have a bad habit of answering my own questions! Why on earth can’t they use CSYNC on pin 5? Meh…
    From HD Retrovision FAQ

    Do your cables use CSYNC to avoid the noise from composite video?

    The SNES/Genesis YPbPr cables do not use CSYNC. However, through the custom design of our cable and its circuitry inside we are able to extract sync from composite video without introducing noise. The two main reasons for this are (1) we are not driving a full video load, and (2) composite video is only traveling over a short distance before being terminated.

    So I need pin 4 on the multi-av out to work at least in some capacity. R45 on the 32X schematic is not directly in the path of pin 4, but completes a little circuit betweeen YOUT and YIN back into the video encoder. Obviously there is already good sync coming out of that pin 6 to R45, so I would suppose the video encoder will want it back to complete the composite signal…unless VOUT already gets sync through the encoder by some other internal routing (doubtful).

    I guess I’ll pre-order the cables and find out this summer!

    edit 2: Yes, the encoder does require that circuit for a complete composite signal, it goes back in for Y/C mix.

    However, do the retrovision cables really require the composite colour information too? Seems I could just short pin 6 directly to CE12, and disconnect pin 20 by a switch or by simply lifting the pin. I would imagine there is the potential for less interference from the ultimately unused colour signal if it’s not passed on to the HD cable. Or I can reconnect R45 and nerf the colour circuit by getting rid of C76 (easier and better method).
    Am I crazy?

    #26363
    mikechi2
    Participant

    Hi Mock, sorry I actually had someone send me their 32x. I could not figure out what was going on and it seems to be a fundamental issue between the 32x’s color encoder and range of tolerance on the 2X’s video ADC. I think the easiest option, by far is to use SCART->Component, the HDRV or wait for RGC’s component option,

    #26365
    Mock
    Participant

    Cool, thanks for getting the hardware and looking into it, much appreciated!

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