Quantcast

Results 1 to 9 of 9

Thread: Proper 50Hz/60Hz mods for Master System/Mega Drive/Sega Saturn? (Crystal Switch)

  1. #1
    Death Adder's minion
    Join Date
    Apr 2011
    Posts
    15
    Rep Power
    0

    Default Proper 50Hz/60Hz mods for Master System/Mega Drive/Sega Saturn? (Crystal Switch)

    Hi all,
    So I have just recently acquired an XRGB-Mini for scaling my retro systems to a HDTV. It works great The problem is some PAL Sega systems suffer from slight 'stuttering' problems when switched into 60Hz using the standard 50Hz/60Hz mods as described here:-
    http://junkerhq.net/xrgb/index.php/Sega_Genesis

    This is due to the crystal oscillators in PAL and NTSC systems using different frequencies, which results in a very slight speed difference (Apparently less than 1% out) this is usually unnoticeable to most users (Especially on CRT TVs etc) but its enough to cause some stutter when using the XRGB-Mini (and possibly on some other scalers/HDTV's as well) Now although I could just swap the systems PAL crystal for an NTSC one, this doesn't really solve the problem since then 50Hz games suffer from stutter instead of the 60Hz versions.

    I am hoping for a mod which would allow the use of two crystals - one for each region (I realise that for true NTSC/PAL output the video encoder would also need to be switched between PAL/NTSC, but lets ignore this for now since I will be using RGB to connect all my systems any way)

    The standard crystal frequency for color encoding NTSC is 3.579545 MHz, and for PAL its 4.43361875 MHz, so all the systems use crystals whose frequency is a multiple of these two base frequencies:-

    -MASTER SYSTEM- (Crystal Oscillator 'OSC1')
    53.693175 MHz - NTSC (x15)
    53.203425 MHz - PAL (x12)

    -MEGA DRIVE- (Crystal Oscillator 'OSC1')
    53.693175 MHz - NTSC (x15)
    53.203425 MHz - PAL (x12)

    -SEGA SATURN- (Crystal Resonator 'X1')
    14.31818 MHz - NTSC (x4)
    17.734475 MHz - PAL (x4)

    AFAIK the Dreamcast should be unaffected by these issues, since all motherboards are identical worldwide(?) and the region is set in the flash memory.

    The Saturn crystal resonators for each region are relatively easy to find, the Master System/Mega Drive crystal oscillators are more difficult, but by searching on Taobao I think I may have found a few suppliers for the 53.693175 MHz oscillators needed (I cant find the PAL equivelant, but this doesnt matter since it can be taken directly from the PAL system being modded)

    -THE MOD-
    The 'simple' method to switch between crystals would be to simply connect wires to each crystal and use a switch to select which one is used, but this is not recommended as you would need to run long wires/traces which is not a good idea when your dealing with clock signals.

    In Argentina some Mega Drive III's came with 'official' 50/60Hz mods which also switched between the crystals, as you can see from this post by chinitosoccer and this picture:-

    Just recreating that circuit would be great, but if we could improve upon it that would be even better (It appears to require three wires)

    What I am hoping for is a circuit board design/schematic which I could use to design a small PCB that could basically be 'dropped in' to the system where the original crystal was (Like the Argentinian Mega Drive pictured above) and would use one high/low pin like the standard 50/60Hz mod to switch between the two crystals (+5V=60Hz, GND=50Hz) this would make it very easy to retrofit this mod to consoles already 50/60Hz modded.

    I have seen the SNES '1CHIP' 50Hz/60Hz mod which uses a similar idea:-
    http://sd2snes.de/files/1chip-5060.pdf
    However i'm not sure if this 74HCU04 design could be used directly with the MS/MD/SS. Also I am guessing two different designs would be needed, since the Master System and Mega Drive use a crystal oscillator, whereas the Sega Saturn uses a crystal resonator.

    Thanks for reading, and for any help/advice you can give me
    Last edited by Link83; 07-05-2013 at 09:21 PM.

  2. #2
    Mastering your Systems Shining Hero TmEE's Avatar
    Join Date
    Oct 2007
    Location
    Estonia, Rapla City
    Age
    30
    Posts
    10,095
    Rep Power
    110

    Default

    You only need the 74AC00 / 74F00 chip arrangement of the SNES 1CHIP mod for this clock swap. The freq is really high however and you need to pay attention to maximum swithing freqs of particular logic gates.
    Death To MP3, :3
    Mida sa loed ? Nagunii aru ei saa "Gnirts test is a shit" New and growing website of total jawusumness !
    If any of my images in my posts no longer work you can find them in "FileDen Dump" on my site ^

  3. #3
    Master of Shinobi
    Join Date
    Sep 2012
    Posts
    1,132
    Rep Power
    29

    Default

    I'm looking for something like this as well so I can have my Saturn with both crystals installed. I've found that using 50hz mode with ntsc crystal will tilt the picture to the left a lot, even with RGB cables... in fact, my Megadrive is also tilted to the left like that.

  4. #4

    Join Date
    Dec 2010
    Location
    Toronto Canada
    Posts
    4,395
    Rep Power
    0

    Default

    Wow, selectable master clock oscillators.

  5. #5
    Death Adder's minion
    Join Date
    Apr 2011
    Posts
    15
    Rep Power
    0

    Default

    Quote Originally Posted by TmEE View Post
    You only need the 74AC00 / 74F00 chip arrangement of the SNES 1CHIP mod for this clock swap. The freq is really high however and you need to pay attention to maximum swithing freqs of particular logic gates.
    Thanks, so just to confirm, this layout should work for MS/MD/SS for switching between crystals?

    Although i'm not sure if anything needs to be changed when using a crystal oscillator for the MS/MD, as opposed to a crystal resonator (plus capacitors/resistors) for the SS?

    The Sega Saturn also already has the capacitors to ground, 1M resistor and 100R resistor to create an oscillator circuit, so is it still nessary to add these components on the above circuit?


    Lastly, its worth noting that the Sega Saturn uses different form factors for the X1 Crystal, which means we cant design a direct a drop-in PCB as i'd originally hoped:-
    Last edited by Link83; 07-05-2013 at 09:12 PM.

  6. #6
    Master of Shinobi MaxWar's Avatar
    Join Date
    Sep 2012
    Location
    Canada
    Posts
    2,042
    Rep Power
    41

    Default

    I do not see an oscillator in My NTSC sms. It only has a 2 pin 10.7386mhz crystal. *It is an older version

  7. #7

    Join Date
    Dec 2010
    Location
    Toronto Canada
    Posts
    4,395
    Rep Power
    0

    Default

    Quote Originally Posted by MaxWar View Post
    I do not see an oscillator in My NTSC sms. It only has a 2 pin 10.7386mhz crystal. *It is an older version
    Yeah that 2 pin crystal is wired into some caps and that's the oscillation circuit. The main chip divides it down to 3.58 mhz and that drives everything on the pcb.

  8. #8
    Wildside Expert
    Join Date
    Dec 2012
    Posts
    115
    Rep Power
    9

    Default

    I'd be interested in buying a crystal from you should you get any NTSC ones as I'd probably just do a straight swap with my current PAL one.

  9. #9
    urusei yatsura Master of Shinobi lumclaw's Avatar
    Join Date
    Jul 2010
    Posts
    1,362
    Rep Power
    17

    Default

    I'd need a PAL crystal, and we all know how rare PAL consoles are here.

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
  •