Megadrive VA0 RGB bypass

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Viewing 15 posts - 1 through 15 (of 16 total)
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  • #23311
    renovigo
    Participant

    Hello there,

    I’m encountering some troubles installing an rgb bypass from Voultar for the megadrive.

    I’ve installed it on a early VA0 japanese megadrive (the one with a little pcb on it), trying to follow the diy installation guide on the videogame perfection website. As this japanese motherboard is made differently, I had to guess where things were corresponding toward the motherboard we see on the site (I think it’s a VA4). For example, the CXA1145 is up and down, I had to deal things in reverse (RGB outputs pins and Csync pin are located in the opposite way).

    It doesn’t work.

    I don’t know if somebody already tried and succed installing the Voultar’s RGB bypass on a VA0 japanese megadrive, but some clues could be good.

    Thanks !

    R

    #23312
    BuckoA51
    Keymaster

    it would help if you describe what doesn’t work exactly, no picture at all or what?

    #23317
    renovigo
    Participant

    Hi,

    Ok so here’s the story :

    I mounted the bypass amp on a VA0 japanese motherboard, so it was a little tricky at the start as it’s a little bit different than the VA4 I used to deal with. I wanted to try on this one because the picture was not good (big big jailbars).

    I first lifted the RGB and CSYNC pins on the 315-5313, in order to isolate completely the signals, and also cut traces on the solder side (the back) which lead to the CXA1145, to be sure. From here I mounted the amp just as discribed on the VDP guide.

    Image is shaking a lot, like CSYNC is not working.

    So I lifted back down the CSYNC pin with the wire still connected on the amp.

    I got an image here, but worse than before, with all kind of interferences, massive jailbars, and red seems to be over charged (like sonic’s skin spent too much time under the sun).

    After trying hasardous manipulations, the CSYNC pin of the 315-5313 broke. I thought all was lost but I managed to get the image described below back, just by maintaining the amp CSYNC wire in place of the CSYNC pin and hold it with tape. Pretty nasty work.

    So, image is still here, but I don’t think I’m going to put my hands inside before knowing exactly how to improve it. If by chance I succed in the improvement, I will have to put glue on that CSYNC wire/pin to avoid it to move.

    Voilà voilà…

    So the actual problems :
    -interferences
    -massive jailbars
    -excessive red (colours are not well balanced)

    #23332
    mikoy
    Participant

    I am doing the same thing with the exact same japanese mega drive board that has the CXA1145 in reverse.

    I can’t get the sync to work! There is no video also if I use a composite video cable.

    Added a resistor from blue pin 29 to cysnch. I also removed a capacitor on the other end of the resistor.

    Board Pictures link

    #23344
    mikoy
    Participant

    Did more changes, lifted the pins on 315-5313 to isolate RGBS. Still not working.

    Please help

    #23347
    BuckoA51
    Keymaster

    No video from composite cable is to be expected as that’s disabled.

    I’m not abandoning you guys, I’ve got a console in at the moment that’s having issues so we’re still investigating.

    #23349
    renovigo
    Participant

    Hi,

    Thanks for all these replies. I’m sorry we’re encountering the kind of same troubles here.

    I digged a little bit more into the problems I got. I’ve been told by the guys from retro rgb that it was maybe better not to lift the csync on the VDP, that’s why I put it back down and it seemed to solve the sync problem.

    Also, concerning the interferences issue, I tried to add a capacitor (16v, 225uf) on the bypass board between the grd and 5v pads, and I got rid of the interferences. I refered to this link here.

    BUT….the image I get is still too dark, too red, and jailbars are still here.

    About not having any image at all, maybe check were you ground your bypass amp. I had this problem at the very beginning, and I got an image by grounding on the daughterboard of the VA0 (there are two little pads right beside the crystal oscillator on the extra little board, I wired the ground on one of them).

    I think I will wait for more users experiences or updated guides from now.

    Thanks

    #23491
    renovigo
    Participant

    Hi there,

    Anyone has some news about solutions, improvements or anything for this VA0 serie ? I keep investigating on my side, but I don’t find anything convincing yet.

    #23632
    bigbear1981
    Participant

    Hi guys, I’m sorry to hear about the troubles you are having with the Japanese VA0.

    Renovigo, you mentioned that you worked on a VA4 model before? Did you have success with installing Voultar’s board there?

    I’d like to install this RGB bypass in my Japanese VA4. But I’m not sure what is the best method.
    Can you tell us the steps you took to get it working well?

    Thanks!

    #23637
    renovigo
    Participant

    Hi,

    Yes indeed I’m used to work on a VA4 model, but unfortunately not for instqlling the bypass board. I just lifted pin 50 on the VDP to get (almost) clean rgb.

    The reason I wanted to install the bypass board on the japanese VA0 was that it has a very dirty rgb rendering, and I was curious to see what the Voultar’s rgb bypass was capable of. But I failed to install it properly, as expressed above.

    Now I’m waiting for more technical precisions.

    Thanks

    #23942
    nzChris
    Participant

    Hi all, sorry to hijack but I’ve been trying to get my bypass board working for a week now with no luck. I’m no expert but have successfully modded my MD1 VA4 PAL with region and cpu overclock mods in the past. I have followed the guide to a tee, although there are some minor differences with my board.

    – Cut all traces from the 315-5313 and left the pull up resistors.
    – Removed the resistor on the csync and installed a 2.2k resistor as suggested.
    – Cut legs 21/22/23 and 10 on the CXA1145, however during troubleshooting I ended up soldering directly from the bypass board outs to the DIN pins directly (and cut the traces by the connector for good measure).

    I have used a multimeter and tested all signals to make sure they get to/form the bypass board and are isolated.

    Various sources have said that you should install a 220uf cap and 470Ω resistor on the csync line in the SCART end of the cable, so I have tried this too.

    My OSSC just says ‘NO SYNC’, anyone have suggestions as to what I could check?

    I have just read this note on retro RGB and wondering if this could be the problem.
    “I suggest soldering to the VDP’s sync pin, but not lifting it, as some model Genesis consoles require the pin for the Z80 to run.”

    #24230
    BuckoA51
    Keymaster

    Various sources have said that you should install a 220uf cap and 470Ω resistor on the csync line in the SCART end of the cable, so I have tried this too.

    Normally you should always do this, but we’ve had a number of PAL systems that absolutely will not work when this is in place, and output perfectly in-spec sync with them removed. Are you saying you’ve tried both ways?

    #24302
    nzChris
    Participant

    Yes I have tried both ways on the csync with a generic cable, I have also bought a retrogamingcables cable to try with no luck. Only thing I haven’t tried/replaced at this point is a different Voultar board.

    #25662
    renovigo
    Participant

    Hi,

    I try to relaunch the japanase VA0 subject. Does anyone found out a solution ? I worked again on it several times, and unfortunately I get no more picture now.

    This board seems to be routed in a very unexpected way.

    Any clues would be welcome.

    Thanks

    #27805
    lugus
    Participant

    Installed the bypass on my va0 today. Followed the guide, respecting board differences. The worst one is the absence of RF modilator on japanese boards. Put my amp above the ym2610 chip (yeah, I know the “right place” is above vdp). Pulled 5v and ground from daughterboard.Heavy jailbars and interference(oscillator is nearby), but picture is ok, notable color vibrancy from the new amp. Then, changed to regulator’s 5v and gnd. Almost solved. The jailbars are still there, but at an acceptable level, after I put thicker and shorter wires.

    Lessons learned: isolate the board the best you can, this thing catches too much interference.

    I finished my installation after viewing this
    https://www.twipu.com/retr0drift/tweet/1074627860529217536

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