New 240p method for PAL 3DO

Discussion in 'Modding and Hacking - Consoles and Electronics' started by Taijigamer2, Sep 4, 2018.

  1. Taijigamer2

    Taijigamer2 Gutsy Member

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    Earlier this year I decided to remove the PAL 3DO video encoder (BT9103) and attempt to replace it with a pin equivalent RGB capable video encoder (BT856).

    IMG_2168(800x600).jpg

    After successfully removing the DAC, I noticed a trace leading away on the motherboard. I traced this to pin 196 on the CLIO. This meant that the CLIO could change the scan mode of the DAC between 480i and 240p provided the game had an instruction in its coding. This is confirmed in the FZ-1 PAL service manual. The DAC is also set to Master mode according to the datasheet which means that Hsync and Vsync are fed back to the CLIO possibly to provide some sort of timing function. This could explain why some games behave weirdly when we force the DAC into progressive mode.

    The service manual shows that PAL 3DO have a resistor (R166) bridging the Interlace signal between CLIO and BT9103. By removing that resistor and soldering a wire to the empty pad on R164, the Interlace pin can be tied high or low without needing to lift the pin on the DAC.

    IMG_2168(240p trace)(800x600).jpg

    (The wires are left over from the previous 240p mod)

    BT9103_240p.png

    IMG_2323(800x600).png

    IMG_2324(800x600).jpg

    I find this method neater than lifting IC pins and risking damage to the board. Remember if it is a Canadian model with BT9103, R164 will need to be removed instead of R166.

    The same method can probably be applied to the VP536 but I don't have a VP536 3DO to test.

    The other wires are part of a DAC transplant RGB mod using an RGB capable encoder. Write up to follow soon...
     

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  2. TheRealPhoenix

    TheRealPhoenix Spoken Language: French & English

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    Nice!
     
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  3. Arnold101

    Arnold101 Active Member

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    this is doable for the jap one too? i want to put that chip onmine for getting rgb
     
  4. kwn

    kwn Member

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    edit: never mind... i missed a paragraph ;)
     
    Last edited: Jul 26, 2019
  5. Taijigamer2

    Taijigamer2 Gutsy Member

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    No worries. I'm still working things out on the 3DO. On the PAL 3DO, pin 197 of the CLIO is able to control the interlace pin of the BT9103 encoder (pin 59) through R166. The signal seems to also be tied to 5V through a weak pull up R167. This might be to ensure the encoder is set to 480i even when there is no signal from the CLIO. By removing R166 (R164 on CAN 3DO) the interlace pin can be switched without unwanted signaling from the CLIO.

    This is also true for JAP FZ1. Removing R166 allows smooth booting and switching to 240p. For FZ-10, R166 isn't present but there is a trace between the pads of R166 which can be cut to the same affect. This can be reversed at any time using a 0 Ohm resistor or solder bridge. @citrus3000psi found this out on his FZ-10.

    As for converting to NTSC, this can be done by moving the resistor on R165 to R163. U will also need to swap the crystal to get correct NTSC timing. The closest I could find was this one https://www.mouser.co.uk/ProductDet...6bBr9Q9abMK2mGYOCsJHDuhD5w63ac%2b1KbfNcj8yg== It should be a direct drop in but I haven't tested it yet.
     
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  6. kwn

    kwn Member

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    I ordered bag of 24.576 MHz crystals and swapped the resistors around to match the CAN 3DO. Doesn't seem to be working right. No colour on both of my PVMs and games flicker quite heavily after changing resolution(?) with the picture being shifted to the bottom. The boot screen looks fine despite the lack of colour... seems like the colour carrier frequency isn't quite right using that crystal. Also it seems to glitch on boot every now and then.
    The service manual also mentions different ceramic caps around the crystal. PAL uses 33 and 22pF and NTSC uses 27pF for both. I haven't replaced those yet. There are also some caps in the AV section that are different between PAL and NTSC models.
     
    Last edited: Aug 8, 2019
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  7. Taijigamer2

    Taijigamer2 Gutsy Member

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    Thanks for testing this. That's unfortunate the crystal isn't quite right. I couldn't find a 24.5454 MHz, this 24.576 MHz was the nearest one. The difference might be enough to throw off the colour subcarrier.

    I worked out the frequency should be stable with the stock caps but the datasheet on mouser states the bridging resistor shouldn't be larger than 50 Ohm, the stock resistor (R143) is 68 Ohm which might throw off the stability.

    Are u using the 240p mod? Are u testing with NTSC games? The other option would be to use a mod board which outputs a set frequency so u can deliver the correct 24.5454 MHz.
     
  8. kwn

    kwn Member

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    I tried it with and without the 240p mod described in this thread. The games I'm testing with are "PAL compatible"... the boxes say "this title displays in a letterbox format on the 3DO PAL system". So I guess they'd be fine on an NTSC (modded) system.
    I thought of using a PLL to generate the correct 24.5454 MHz but haven't gotten around to doing that yet.
     
    Last edited: Aug 17, 2019
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