MegaDrive 1 CXA1645 mod

Discussion in 'Modding and Hacking - Consoles and Electronics' started by Bearking, Mar 29, 2011.

  1. Lum

    Lum Officer at Arms

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    Genesis 2 definitely has an issue of the sort in my setup. I haven't ruled out whether the cables are to blame, or if using c-sync would help. I don't own MD2 at the moment to check that.
     
    Last edited: May 14, 2012
  2. Fireball haven

    Fireball haven Active Member

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    It's not surprising the CXA output will have a high level like that, the level should be 0.287 * 2, and it probably is with a 2V offset which is removed by the cap. You can't really trust what a multimeter tells you, it's a relatively fast AC signal and the meter will just give you the RMS voltage, not the true Vpp without respect to duty cycle. For that you need a scope.
     
  3. JimmyCrackCorn

    JimmyCrackCorn Spirited Member

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    Where would c28 be on my model 1 motherboard? It looks nothing like the motherboards you guys are posting!

    [​IMG]
     
  4. ApolloBoy

    ApolloBoy Gutsy Member

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    The part numbers are labeled on the top of the board, not the bottom. What revision do you have?
     
  5. JimmyCrackCorn

    JimmyCrackCorn Spirited Member

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    Nope, there's no numbers on the other side of my board corresponding to which capacitor is C28. However, I was able to figure it out by tracing it to VPN pin 50. I removed it, but I want to create a switch so I can turn it off and on. What is the specs of this resistor (C28) so I can buy a replacement?
     
  6. Druidic teacher

    Druidic teacher Officer at Arms

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    Last edited: Jun 22, 2017
  7. JimmyCrackCorn

    JimmyCrackCorn Spirited Member

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    You ended up being correct. Thank you so much. Do you have any idea what the rating is for this capacitor? I'd like to install a switch to the back of the system so I can turn it back on for when I need to use S-Video (like when I want to play Master System since you can't do that with the 32x plugged in) but I'm not sure what size resistor it is, and I'm not sure which way is negative and positive and such. If anyone knows, please tell me!
     
  8. Druidic teacher

    Druidic teacher Officer at Arms

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    Last edited: Jun 22, 2017
  9. JimmyCrackCorn

    JimmyCrackCorn Spirited Member

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    The metal point came off the microscopic resistor when I removed it, so measuring it would be impossible. I'm actually kind of surprised there's no spec sheet out there somewhere that states every resistor and capacitor in the Genesis/MegaDrive and their values!
     
  10. Druidic teacher

    Druidic teacher Officer at Arms

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    Last edited: Jun 22, 2017
  11. JimmyCrackCorn

    JimmyCrackCorn Spirited Member

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    Thanks for all the help, guys. I was wondering, what amp are you guys using in the Genesis to go right from RGB to the cable? Meaning, not passing through an encoder? I tried this with the SNES to try and remove the thick vertical line issue, and I get this as a picture:

    [​IMG]


    Again keep in mind I completely desoldered the stock encoder so I can see if the encoder is the culprit. So I guess the encoder actually has an amp in it! However, I am not sure why the red in my pic is so streaky? Why would this happen? It's going right to an XRGB Mini. Sorry if this is a bit off topic; I just figured I could use whatever amp was used in post #72.
     
  12. Lum

    Lum Officer at Arms

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    Master System and Genesis hardware architecture is too different from SNES for that.
    Entirely different looking vertical bars with unrelated causes.
     
    Last edited: Oct 23, 2012
  13. Anar

    Anar Member

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    good day. i have a sega with mc13077 Ic, as i see it have RGB inputs, but not outputs, i want to use cxa1145 as rgb encoder, can anyone help me?
    i drawing a picture how its could be, but i think there was i mistake.
    p.s. sorry for my bad english.
    IMG_20131226_111410.jpg
     
    Last edited: Dec 25, 2013
  14. l_oliveira

    l_oliveira Officer at Arms

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    SONY video encoders are quite "anal" about having the sync input at 2v level. I don't see why that would not work as long you keep the 2v thing in mind.

    Maybe if you copy the original circuit from a legit Mega Drive console it would work for you. (just the sync part, the stuff you already drawn looks fine, mostly but the sync part is wrong).


    Edit: just making sure you understand, the CXA1145 REQUIRES SYNC for the proper operation of the clamping circuit on the RGB amplifier. No sync, no output.
     
    Last edited: Dec 26, 2013
  15. Anar

    Anar Member

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    i get the sync in from 13077 and connect it to 1145, and from 1145 sync out connect to composite in the scart cable, but the image was a dark red .
     
  16. APE

    APE Site Supporter 2015

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    I'm aware of at least one person who put a cxa2075 into their Genesis. Seems to work pretty well for them.

    Last time I tried to assemble a 1645 circuit it fried on me and haven't had the desire to buy another for fun.
     
  17. l_oliveira

    l_oliveira Officer at Arms

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    That's because you have a clone megadrive and it's circuit is made for the MC13077. Sync signal voltage is WRONG for the CXA chip.
     
  18. Anar

    Anar Member

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    and what can i do?
     
  19. l_oliveira

    l_oliveira Officer at Arms

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    Copy the electronics schematic of the real Mega Drive maybe ... That's what I said the first time.
     
  20. Anar

    Anar Member

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    i made a rgb amp today, but in image i cant see the white color, i made screenshots. what i do wrong?

    http://www.emu-land.net/forum/index.php?action=dlattach;topic=68385.0;attach=73160;image
    http://www.emu-land.net/forum/index.php?action=dlattach;topic=68385.0;attach=73158;image
    http://www.emu-land.net/forum/index.php?action=dlattach;topic=68385.0;attach=73156;image
     

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    Last edited: Dec 30, 2013

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