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Getting the Megadrive to output 60hz in colour

Discussion in 'General Tech Help & CD Burning Help' started by Mangaman, Feb 14, 2002.

  1. Mangaman

    Mangaman New Member

    Okay, I was just thinking - you know how you can add a simple colour correction mod on a PSX/PSone/PS2 so that it outputs 60hz signals in colour, do you think it would be possible to do the same on the Mega Drive?

    On the PSX prior to adding the mod, the picture was black and white, like the Mega Drive's... it's just a thought, but does anyone here think that it may be possible to do something similar? I might pop open my system and fiddle around, but I figured I'd bring it up here anyhows.

    If nothing else, it's a little food for thought.

    -Mangaman-
     
  2. IceDigger

    IceDigger Founder Staff Member

    not that easily, no. the psx video processor can actually be forced to output PAL at all times, the genesis one in 60 Hz can't.

    if you have a RGB capable TV, buy/make a RGB cable and you get color at 60 Hz too (and the best possible picture to boot).
     
  3. Mike G

    Mike G New Member

    The CXA1145 (or 1645 in later models) in the MD can be forced to output PAL, but it needs the correct clock signal (4.43MHz for PAL, 3.58 for NTSC).

    A suitable mod would be similar to the colour mod for the very early Playstation models (i.e. add a crystal oscillator to generate 4.43MHz at all times). Never tried it myself as I always use RGB ;)

    Mike
     
  4. Mangaman

    Mangaman New Member

    Mike G,

    That sounds very cool... but how do I change it? I don't have my megadrive open atm... could you give some details so I know what to do and what to buy? Just so that if I go into my electronics store, what part I have to ask for...

    Thanks heaps!

    -Mangaman-
     
  5. Norwix

    Norwix New Member

    You can get pal 60hz in colour with a 32x (with cart games or cd games) :)
     
  6. Mangaman

    Mangaman New Member

    I'm aware of this and it doesn't help me since I lack a 32X and don't want to pay the huge price they go for on eBay.

    I would be very happy if I ever came across one in a second-hand store, I can tell you!

    -Mangaman-
     
  7. Mike G

    Mike G New Member

    Mangaman,

    Which version of the Mega Drive do you have? (MD 1 or 2?)

    Mike
     
  8. Mangaman

    Mangaman New Member

    I have two megadrive 1s - one has the modem port, the other doesn't. There's also a Megadrive 2 I want to mod as well, so if you could supply info for both if possible, I'd be really grateful.

    Thanks!!!

    -Mangaman-
     
  9. Mike G

    Mike G New Member

    Right...

    I'm not 100% sure of the Mega Drive 2 details at the moment, so I'll leave that to one side for now.

    The following information applies to the Mega Drive 1, which contains a 24-pin Sony chip labelled CXA-1145. (You'll need to remove the big heat sink that's attached to the two 7805 voltage regulators in order to get at it.) This chip is the composite colour encoder which converts RGB to PAL or NTSC video.

    The first thing you need to do is desolder three pins of this chip - pins 5, 6 and 7 - and lift them clear of the board. (Alternatively you can just cut the pins close to the board and lift up what's left.) The idea is to disconnect these three pins from their respective board holes.

    Pin 7 is easy to deal with; just connect a wire between it and pin 1 (Ground). This is the PAL/NTSC select pin; connecting it to ground enables PAL output.

    Now you'll need to go to the electronics shop and buy 4 components:

    4.433619MHz Crystal (a.k.a. PAL Colour crystal)

    15K Resistor (metal film type)

    30pF Capacitor (ceramic disc)

    50pF max. Variable Capacitor (a.k.a. 50pF max. Trimmer)

    If you can't find a capacitor of exactly 30pF, use a 33pF one. The trimmer max. value isn't so important, so long as it's less than about 100pF (and more than 40pF) it should be fine.

    The crystal value is critical, however.

    All of these components are non-polarised, i.e. it doesn't matter which way round you connect them.

    Now, the next step is to build the circuit. The rather crap diagram here:

    http://www.mikeg2.freeserve.co.uk/masterful/colmodmd.gif

    shows how the components should be connected together; how you go about this is up to you.

    Personally I would get a small piece of prototype board or Veroboard and build the circuit on that. You can just solder the legs of the components together (as shown in the diagram) if you prefer, but it won't be as neat. (Ensure the component legs aren't touching anything! Wrap in insulating tape if necessary.) Make sure you can access the variable capacitor once you've put the heatsink back on, since you'll need to adjust it...

    OK, refit the heatsink, and switch on your MD with a cart inserted. You'll probably get a black and white image. Now simply adjust the variable capacitor with a screwdriver, in small increments, until you get a nice colour picture. Make sure that it works in both 50Hz and 60Hz modes.

    Remember that I haven't tried this myself; you do it at your own risk! I'm simply going by the CXA-1145 spec. sheet.

    Best wishes,

    Mike
     
  10. Mangaman

    Mangaman New Member

    Mike,

    What can I say - you are an absolute legend!!!!!

    I'll give the mod a whirl tomorrow and post back here with the results... thanks again mate!

    -Mangaman-
     

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