Quantcast

Page 1 of 2 12 LastLast
Results 1 to 15 of 21

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

  1. #1
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

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

    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


    Proto boards:

    For Model 1 VA5-6, with remote:


    For Model 2 VA-1.8, automatic:



    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:


    Designs and Layout:

    The Remote:


    Model 1:


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




    Model 2:


    Exemple of layout:



    Variation and adaptation of the original designs:

    Model 1 - full auto/no remote:



    To be tested:

    32X - patch the missing signal:


    Last edited by The Real Phoenix; 04-06-2015 at 05:00 PM. Reason: add pics

  2. #2
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    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.

    - I heard the Genesis 2/Megadrive 2 needs a 4 pins Crystal oscillator
    - The board for the Genesis 2/Megadrive 2 uses a 74HC04 working as a driver for a 2pins Crystal (easier to find).


    - 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 anymore!
    - 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 by The Real Phoenix; 03-27-2015 at 11:37 PM.

  3. #3
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    To do: adding screenshots and video
    Last edited by The Real Phoenix; 03-22-2015 at 01:39 AM.

  4. #4
    Wildside Expert
    Join Date
    Aug 2013
    Location
    Portugal
    Posts
    199
    Rep Power
    8

    Default

    Very interesting, I've done something similar but all manual with 2 switches, one for selecting PAL or NTSC encoding and another for 3.58 or 4.43 MHz, you can set 4 color systems on either 50 or 60Hz:

    -Pal 4.43 50/60
    -Pal 3.58 50/60
    -NTSC 3.58 50/60
    -NTSC 4.43 50/60

    By doing manual overrides you can set to PAL60 or NTSC50 I've also put in a chroma killer switch to eliminate jailbars in RGB mode.

    http://www.sega-16.com/forum/showthr...opinion-needed

  5. #5
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    Yeah it's pretty much the same thing.
    I isolated both circuit and you can add the remote if you want to force the signal.
    I also added the ability to activate/desactivate the board, but it just let the original signal go thought. I could add a chroma killer thought.

  6. #6
    Sports Talker
    Join Date
    Jan 2015
    Posts
    37
    Rep Power
    0

    Default

    Does your board completely disconnects pins 5 and 6 from the genesis' motherboard? It should, I think.

  7. #7
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    I keept the original signal for when you desactivate the board it restores the original "parameters" of the console.

    You can change the circuit and totaly cut it off, but this will result a black and white picture in Svideo/Composite if you desactivate the board.

  8. #8
    Video Game Modder Outrunner segasonicfan's Avatar
    Join Date
    Nov 2009
    Location
    California
    Posts
    602
    Rep Power
    21

    Default

    This is AWESOME! What a cool idea!
    Now this won't do NTSC 50hz because the Sega ASIC internally changes the Sync pulse to 50HZ which will freak out almost any TV that is meant for NTSC. Some portable LCDs will swap between the two though, and a commadore 1084 monitor will do it too.

    By fixing the "Waving" do you meant the rainbow banding that moves along the edges of everything? I've been trying to fix this on my home made circuits forever, does your circuit improve this? It looks you have a variable capacitor in there to adjust it(?)

    -Segasonicfan

  9. #9
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    Yes, it like the rainbow banding but much more attenuate and only on the edges of sprites.
    You have to tweak those trim capacitor and this will stabilize this.

    Right now I still didn't find time to make a vids about that mod.

  10. #10
    Video Game Modder Outrunner segasonicfan's Avatar
    Join Date
    Nov 2009
    Location
    California
    Posts
    602
    Rep Power
    21

    Default

    Quote Originally Posted by The Real Phoenix View Post
    Yes, it like the rainbow banding but much more attenuate and only on the edges of sprites.
    You have to tweak those trim capacitor and this will stabilize this.

    Right now I still didn't find time to make a vids about that mod.
    I would LOVE a video showing what the tweaking looks like for fixing the banding. If I could fix that issue I would be in heaven

  11. #11
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    I hope I could find some time at least to film and make some rushes next week-end.

  12. #12
    Wildside Expert
    Join Date
    Aug 2013
    Location
    Portugal
    Posts
    199
    Rep Power
    8

    Default

    It's not banding per se, the pot will alter the chroma frequency, on the TV you will see dot crawl on the edges of objects on the screen, when adjusting the pot you notice that those dots will either look stationary or it will be moving and the movement speed will vary as you turn the pot, when I did the mod I can't remember if you should leave them stationary or moving the fastest for best compatibility.

    I remember that I was adjusting on my LCD for what I thought looked best and it never lost colour no matter how I turned it but when I hooked it up on a CRT it showed in black and white because the frequency wasn't quite there yet, so I had to turn to the opposite setting and now it shows colour on all my TVs. I also found that PAL is more sensitive to these frequency tweaks.

    I'm not 100% positive but I think stationary is the way to go, as moving the fastest was what looked best to me as you almost couldn't see them, but the CRT wouldn't show it in colour.

    I hope what I said made any sense.

    http://en.wikipedia.org/wiki/Dot_crawl

  13. #13
    Death Adder's minion The Real Phoenix's Avatar
    Join Date
    Oct 2014
    Location
    Montréal
    Age
    39
    Posts
    23
    Rep Power
    0

    Default

    Yes, it's exactly that:! Thanks!

  14. #14
    Video Game Modder Outrunner segasonicfan's Avatar
    Join Date
    Nov 2009
    Location
    California
    Posts
    602
    Rep Power
    21

    Default

    Quote Originally Posted by t0nito View Post
    It's not banding per se, the pot will alter the chroma frequency, on the TV you will see dot crawl on the edges of objects on the screen, when adjusting the pot you notice that those dots will either look stationary or it will be moving and the movement speed will vary as you turn the pot, when I did the mod I can't remember if you should leave them stationary or moving the fastest for best compatibility.

    I remember that I was adjusting on my LCD for what I thought looked best and it never lost colour no matter how I turned it but when I hooked it up on a CRT it showed in black and white because the frequency wasn't quite there yet, so I had to turn to the opposite setting and now it shows colour on all my TVs. I also found that PAL is more sensitive to these frequency tweaks.

    I'm not 100% positive but I think stationary is the way to go, as moving the fastest was what looked best to me as you almost couldn't see them, but the CRT wouldn't show it in colour.

    I hope what I said made any sense.

    http://en.wikipedia.org/wiki/Dot_crawl
    Thank you for all this info and the link above. Here is a video of the problem I am having, it looks like rainbow banding + dot crawl, I am not sure what is going on exactly:

    http://s18.photobucket.com/user/Sega...q5rhz.mp4.html

  15. #15
    Wildside Expert
    Join Date
    Aug 2013
    Location
    Portugal
    Posts
    199
    Rep Power
    8

    Default

    Is your console crystal modded or original? That is a weird problem as the image is shaking horizontally, dot crawl usually "travels" up and down, not sideways.

    EDIT: Actually I just connected my Megadrive in composite mode (I usually use RGB) and the dot crawl is actually scrolling sideways when in NTSC mode. Your problem may be related, also some TVs deal with chroma better than others.
    Last edited by t0nito; 04-09-2015 at 03:07 PM.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •