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Thread: Help with Genesis 2 S-Video mod (CXA1145M encoder) - No signal. - FIXED!!!

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    Peach (Level 3) izarate's Avatar
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    Smile Help with Genesis 2 S-Video mod (CXA1145M encoder) - No signal. - FIXED!!!

    My Genesis 2 has a Sony CXA1145M video encoder instead of the Samsung encoder (lucky me). I've built the buffers as per this instructions that a lot of sites refer to:
    http://www.gamesx.com/wiki/doku.php?..._1_s-video_mod

    I also found some information on this thread:
    http://www.digitpress.com/forum/showthread.php?t=82298

    I'm using 100K + 10K resistors instead of a single 110K resistor, a C1815 instead of the NTE85, and a 68 ohm resistor on the C output since I couln'd find a 75 ohm resistor, but as far as I can tell, it shouldn't matter.

    The bad thing is that I'm not getting any signal on the TV. I then thought that maybe the "M " after the CXA1145 might have something to do with it, but it's just a smaller revision with the same capabilities as the regular CXA1145.

    I have tried:

    - testing the buffers for shorts,
    - connecting Gnd to the heatsink instead of the G pin on the regulator,
    - connecting the buffer Gnd to the regulator's G pin and the S-Video Gnd to the heatsink,
    - the inverse of the above,
    - switching the Pin 16 and 15 connections to the buffer board, just in case I got them reversed somehow,
    - connecting the shield of the S-Video jack to Gnd,
    - making another set of buffers with the 2N3904 instead of the C1815.

    Am I missing something? Why am I getting no signal on the TV?

    Pictures:
    CXA1145M in Genesis 2 (board revision PC BD MD2 VA1 USA):

    The circuit I'm using:
    Last edited by izarate; 12-08-2007 at 11:14 AM. Reason: grammar

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    Pac-Man (Level 10) FABombjoy's Avatar
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    Well, it should work, so you're not crazy Do you have a pic of the circuit?

    Does your test monitor have a blue screen when no video is present? If so, they can make troubleshooting these kinds of things a real chore.

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    Peach (Level 3) izarate's Avatar
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    I mounted the circuit on a little project board:





    The S-Video Gnd on those pics comes from the heatsink, but it came from the Gnd on the project board before I started to try crazy things.

    Since I couldn't get a panel mount jack, I intent to use a thin S-Video cable that I had lying around to connect the circuit to the TV. The cable can get through the little hole that is in the right side on the back of the Genesis (what was it for anyway?).

    The TV keeps a black screen with the tag Video 1,2,3... when no signal is present. When it gets signal, the tag disappears after 2 seconds.

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    Banana (Level 7) davidleeroth's Avatar
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    Just had a quick look but in the components pic you have B in the center for the C1815 when, according to datasheets, it should have C.

    "I never should the games I sold and I have replaced them but they are not the game just a hollow shell of the same game." -RugalSizzler

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    Peach (Level 3) izarate's Avatar
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    Thank you. I don't know how I got wrong the pins in the first place, but yes, that's correct. I'll change the transistor orientation and come back with the results.

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    Pac-Man (Level 10) omnedon's Avatar
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    That looks like the mod for the Genesis 1/NEO GEO AES encoder CXA1645. In my experience all the CXA1145M requires is a direct tap of luma and chroma, then a 75ohm resistor (and of course ground to the jack ground pins). Connect the resistors to luma and chroma on the jack, and voila. S-Video.

    Your circuit is gorgeous bt the way. Beautiful work, but unless I'm having some sort of brain fart, that circuit is for the other video encoder, and should not work with your Genesis2.
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    Insert Coin (Level 0) gumbyandpals's Avatar
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    As far as I know he's doing the right mod. The genesis 1 has a cxa1145 chip and his genesis 2 happens to have one as well. I think it's more common for the Genesis 2 to have the cxa1645 chip which just needs some resistors. So I think that's what you're thinking.

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    Pac-Man (Level 10) FABombjoy's Avatar
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    Quote Originally Posted by omnedon View Post
    Beautiful work, but unless I'm having some sort of brain fart, that circuit is for the other video encoder, and should not work with your Genesis2.
    Brain fart, check

    The 1645 doesn't need the buffer, 1145 does.

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    Pac-Man (Level 10) omnedon's Avatar
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    Well, we've got that out of the way... =)
    ... for your gaming and iPod service needs http://www.oldschoolgamer.com/ For all your Video Game console and iPod upgrade/repair needs!

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    OK, I'm going nuts...

    This is the revised circuit. Same components. Still no picture.

    The connections:


    I've tried:
    - connecting Gnd to the heatsing instead of the G pin on the regulator,
    - connecting the S-Video shield to Gnd,
    - conecting the cable directly to the TV, bypassing my A/V selector.

    The only thing I haven't done yet is to lift the pins of the CXA1145M from the board. Pin 15 is grounded, but pin 16 is connected to some circuitry. I've seen mod guides, but they are for the Genesis 1 and none shows the pins being lifted. Have anyone from here modded a Genesis 2 that had the CXA1145 with success? Should I lift the pins?
    Last edited by izarate; 01-09-2008 at 06:56 PM. Reason: added thumbnail

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    Peach (Level 3) izarate's Avatar
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    I noticed something weird:

    Genesis cart: No signal
    Pic:


    Sega CD intro screen: Wavy B/W signal. The image scrolls down fast.
    Pic:


    Once the Sega CD game loads, the TV doesn't receive a signal again, as with the carts. I know that the Genesis is still working because the TV still plays the sound.
    Last edited by izarate; 12-08-2007 at 07:38 AM.

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    Pac-Man (Level 10) FABombjoy's Avatar
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    The last time I saw a picture like that, one of the transistors had a bad connection to +5.

    You may want to focus primarily on luma until you get a stable picture. That way, you're only debugging 1/2 of the circuit, and the other half is free to compare with. That's what I've had to do in the past.

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    Peach (Level 3) izarate's Avatar
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    Talking Success!!!

    Quote Originally Posted by FABombjoy View Post
    The last time I saw a picture like that, one of the transistors had a bad connection to +5.

    You may want to focus primarily on luma until you get a stable picture. That way, you're only debugging 1/2 of the circuit, and the other half is free to compare with. That's what I've had to do in the past.
    Well, turns out that the 68 ohm resistor was the culprit. Once I put a 33 ohm resistor in the chroma buffer, it worked. o_O

    I still can't understand why it wouldn't at least work with the 68 ohm resistor. As far as I know, it should just provide a darker picture but it would still work. Anyway, I'm happy now that my tribulation is over.

    Pics:


    I had to remove the S-Video jack shield because of the limited space.


    There is the S-Video cable, going out from the little hole that is at the side of the A/V out.


    It sure beats RF.

    Thanks to all you people for posting here.
    Last edited by izarate; 12-08-2007 at 01:21 PM. Reason: added quote

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    Alex (Level 15) InsaneDavid's Avatar
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    Nice work to get it working! I figure I'll wrap up the last of this thread's questions...

    Quote Originally Posted by izarate View Post
    The cable can get through the little hole that is in the right side on the back of the Genesis (what was it for anyway?).
    The little hole on the back usually has a small threadded plate on the inside, looks kinda like a little M. It's the first part that goes missing when you open the console unless you're expecting it to fall out. The hole and threadded plate are there to accept a small screw that holds the Power Base Converter in place - completely useless since it doesn't require being screwed down to the system.

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    Strawberry (Level 2) 77punk's Avatar
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    nice,thanks 4 the pix
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    Quote Originally Posted by InsaneDavid View Post
    Nice work to get it working! I figure I'll wrap up the last of this thread's questions...



    The little hole on the back usually has a small threadded plate on the inside, looks kinda like a little M. It's the first part that goes missing when you open the console unless you're expecting it to fall out. The hole and threadded plate are there to accept a small screw that holds the Power Base Converter in place - completely useless since it doesn't require being screwed down to the system.
    I lost my screwy thing! lol

    seriously though, even though I modded my model 1 system with RCA stereo jacks and component video, I try to keep all stock parts in it, and that seems to be the only missing part.

    Crap, to a local junk yard to find an old dead Genny for it's M screwy thing.

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    Strawberry (Level 2) 77punk's Avatar
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    looks like i might have fried something cause now even with the normal setting the screen is very dark. Ugh at least i tried it on a spare one and not the good one.

    Do you have pictures of the bottom of this mod?
    Thanks
    Last edited by 77punk; 10-24-2008 at 01:30 PM.
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    Peach (Level 3) izarate's Avatar
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    You shouldn't use the same layout unless the circuit board is the same I used.

    Here is the picture of the bottom of the board I used:


    The S-Video pinout is fine. Just remember that the pinout is reversed in the female side (the one you'll solder).

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    Strawberry (Level 2) 77punk's Avatar
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    Im using just left over plain circuit board so i can easily copy yours. I think i fried the last system but i did spend some money so im going to attemp it again. I wish i had a better camera.
    The only area im skeptical in is the pin 15 and 16 entering into the capacitor. It should go through the yellow disk shaped thing on one leg and go into the blue capacitor with the flow of the arrow?



    Quote Originally Posted by izarate View Post
    You shouldn't use the same layout unless the circuit board is the same I used.

    Here is the picture of the bottom of the board I used:


    The S-Video pinout is fine. Just remember that the pinout is reversed in the female side (the one you'll solder).
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    Peach (Level 3) izarate's Avatar
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    The capacitors must be placed in parallel, and the signal from pins 15, 16 must enter the dielectric capacitor from the negative side. The negative side is the one with the arrows so, if I understood you well, your capacitor is backwards.

    The ceramic capacitor doesn't have polarity so it doesn't matter how you place it.

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