[Megadrive/Genesis model 1&2] Dual Crystal PAL/NTSC color fix restoration.

Discussion in 'Modding and Hacking - Consoles and Electronics' started by TheRealPhoenix, Mar 15, 2015.

  1. TheRealPhoenix

    TheRealPhoenix Spoken Language: French & English

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    Hi everyone!

    This is a thread about all my researches for a universal PAL/NTSC Color restoration circuit for the Megadrive/Genesis model 1 and 2.

    It's all begun with my switchless mod where I wanted to have color on PAL for a NTSC Megadrive.
    For european it's easy to slap a 4.43Mhz and have a PAL60Hz console, but for NTSC it's more complicated.

    This is a kind of experiemental for me, I had and still have a lot of advances and steps back.
    But since some of you ask me to share my work, there you go!



    /!\ I WON'T BE RESPONSIBLE IF YOU BROKE SOMETHING!! /!\



    PLEASE READ:

    • First: I don't have much experiment in electronics, only basic stuff.
    • Second: Most of my work is based on already working circuit from Mmmonkey and Zipplet
    • Finally: I may have wrong on some stuff, so don't yell at me; Please correct me, share what you know and let's improve this circuit!



    What I wanted:

    - exact colors on PAL and NTSC, no more derivated signal from main clock
    - detection of the videot signal from the console,
    - autoswitch the the right Crystal,
    - can override the video signal and use the acoordinate Crystal
    - can be disabled


    How it's working:
    - Board is feeded by +5V, Ground, Video Signal signal (like JP3/4 or Pin 7 of the video chip) and Color Signal (from pin 6 of the video chip)
    - The board as to be somehow between the video chip and the signals from the motherboard
    - It intercepts the Video Signal, compares it from what you want (PAL is Ground, NTSC is +5V) then a 74HC4052 open the right circuit with a 2 pins Crystal and what it needs to work.
    - The automatic and override mod need to have the opposite of the video signal, thus there's a signal inverter in the design
    - Basic mods are:
    - Disabled: do nothing
    - Automatic: detects the Video signal and acoordignly use the right Crystal
    - Override: ignore Video signal and force what you what with the right Crystal​


    Tests:
    The tests were run on:

    - Model 1 VA3-USA / CXA1145P
    - Model 2 VA1.8-USA / MB3154PF
    - Model 2 VA1.8-USA / KA2195D

    to confirm:

    - Model 2 VA1.8-USA / CXA1145M (I need to replace a KA2195D for a Svideo mod, so I'll confirm that soon)


    The Results:

    So far, the result is mixed.


    • The color resoration IS working BUT you need a NTSC/PAL TV.
    • It does work with Svideo
    • As I suspected, I do have better colors even in NTSC, like when you add a 32x, but it depends of the console and the TV (or the receiver or converter). I'll try to capture that but it's hard.
    • Adjusting the "waving" of the final bard with variable resistor is a pain.
    • KA2195D seems to not working in PAL, which is at the same time normal from the datasheet, and weird since I thougt I had colors in PAL while debugging my protoboard.
    • The NTSC50HZ (NTSC signal, 4.43Mhz Crystal) doesn't work. TV will either don't do anything, don't sync or just shit in their pants
    [​IMG]


    Proto boards:

    For Model 1 VA5-6, with remote:
    [​IMG]

    For Model 2 VA-1.8, automatic:
    [​IMG]


    Installation:

    Naming convention:
    - SRC: Original Video Signal. Ground for PAL, +5V for NTSC
    - DST: Signal sent to the Video Chip
    - INV: Inverse of the Video Signal
    - COMP: What you are using to compare to the original signal
    - MB: From the motherboard
    - PIN: To the video Chip

    Note 1: if MB and PIN are required it means they are not connected: as exemple lift the pin from the video chip, use the pad as MB and the lifted pin as PIN.
    Note 2: if you don't want to use the remote and let the board as automatic, you can bridge SRC+DST and INV+COMP.


    Installation in the Model 1:
    - Remove the CXA,
    - Put a DIP machined round holes sockets
    - put the board
    - place the CXA
    - Either plug the remote or bridge the points

    Installation in the Model 2:
    - Remove the R61,
    - add the correct resistor value on the board: if you are using a MB3154, then it's 4.7k, else it's a 10k
    - For a override control, you need to left the pin 7 or cut the trace to the it. Before the cut should be "MB7" and after "PIN7"
    - Either plug the remote or bridge the points


    Exemple of protoboard in the Model 2:
    [​IMG]

    Designs and Layout:

    The Remote:
    [​IMG]
    [​IMG]

    Model 1:
    [​IMG]

    Exemple of layout (Trought hole and SMD):
    Beware that the CXA is upside-down between VA3-4 and VA5-6
    [​IMG]
    [​IMG]


    Model 2:
    [​IMG]

    Exemple of layout:
    [​IMG]


    Variation and adaptation of the original designs:

    Model 1 - full auto/no remote:
    [​IMG]


    To be tested:

    32X - patch the missing signal:
    [​IMG]
    [​IMG]
    [​IMG]
     
    Last edited: Mar 21, 2015
  2. TheRealPhoenix

    TheRealPhoenix Spoken Language: French & English

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    F.A.Q:


    - I don't understand what your circuit does.
    - After a Region mod on a Sega Genesis/Megadrive model 1 or 2. By changing forcing the region (Pal or Ntsc), the frequency calculated from the main ocsillator is wrong resulting a black and white color. This circuit is design to restore color.


    - If the Genesis/Megadrive have the colors in its original region, why don't you just use it?
    - The color signal is approximated since it derivated from the main clock of the console. This circuit is using exact frequency.


    - Ok, but does it make any change?
    - Some TV are sensible to this signal. I did observe a better quality, but it depends of your TV and the video chip of your console. Unfortunately after so much time of working on it I'm not sure anymore :(.


    - Does it get rid of the jailbars?
    - I don't have jailbars on the 3 Genesis/Megadrive which where my test subjects, so for now I don't know.


    - Is it compatible with the S-video mod?
    - Yes it is.


    - Does it interfere with the RGB?
    - No. But just in case, you can add the remote which can disable the board.


    - I'm in US. Does it mean I'll have colors in PAL on my TV?
    - You need a TV compatible with the signal your are sending. In Europe, you can send a NTSC signal with a PAL colors: It's called PAL60. But unfortunatly, the opposite (PAL signal with NTSC colors) is not working.


    - I made a board with your schematic; It works but I have a "waving" effect on the screen.
    - Use the trim capacitor to stop the waving.


    - Your circuit is awfully designed/too much complicated: you can do ***** or ******.
    - Sure, maybe, share your knowledge and let's improve this board!


    - Why are you using this component and that chip ? This is stupid!
    - Yes, I'm sorry, I don't have much experiment in electronics, only basic stuff.


    - I made a board like you now my console is not working again!
    - I'm sorry for your console, but I did myself a lot of proto, and all of my genesis are still alive.




    - To be completed -
     
    Last edited: Mar 22, 2015
  3. TheRealPhoenix

    TheRealPhoenix Spoken Language: French & English

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    To Do: I'll try to add comparative quality pics and a make a video.
     
    Last edited: Mar 15, 2015
  4. EmileS

    EmileS Newly Registered

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    Interesting post!

    I have the same issue with my Mega Drive 1. In 60hz mode my picture gets off-canter and flickering due to the wrong frequency in the video signal. However I am looking at a more simple solution.

    Would it be possible to desolder the PAL crystal of 53.203425 MHz, put it on a board with my NTSC crystal of 53.693175 MHz from aliexpress, and just put a switch between the 5V supply on the crystals and have both outputs go back the the Mega Drive motherboard?

    Then I would be able to have a DPDT switch for my region mod that also switches between my two crystals? Seems pretty simple.

    I understand that you want to automate your solution, but do you think the above would work?
     
  5. TheRealPhoenix

    TheRealPhoenix Spoken Language: French & English

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    Yes, this is the best solution. In fact, now you can eve use programmable oscillator. I'm currently working on an other way to do this mode. I wish I would have more time.
     
  6. Helder

    Helder Site Supporter 2014,2015

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    You're referring to the programmable oscillator that Micro developed? That is the best method in my opinion and is a drop in replacement for the main oscillator in the Genesis models.

    You can use the same logic of your boards to do the switching and no other caps or crystals/oscillators needed.
     

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