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Adding RGB scart to a Sega Master System.

Discussion in 'General Electronics Discussion' started by NeilTheDruid, Nov 25, 2011.

  1. NeilTheDruid

    NeilTheDruid

    6
    0
    Jun 21, 2011
    Hello everyone,

    For a bit of fun I'm having a go at adding a SCART socket to my Sega Master System. Currently I'm using a guide here. This modification involves soldering to the systems video encoder. The video encoder I have in my system is not the one in the guide - mine is an MB3514 - datasheet here. The pinout is the same as the one in the guide. I have assembled all the circuit in the guide and currently I'm getting a distorted and rolling image (although the right image is in the fuzz). I've checked the pin voltages against the values here and have found out that the voltages are too high, here are my voltages at the socket:

    Red (Pin 15) - 1.1-1.2v
    Green (Pin 11) - 1.7v
    Blue (Pin 7) - 2.3v
    Composite/Sync (Pin 20) - 1.46v
    RGB switch (Pin 16) - 5.05v

    I am wondering if anyone can help me out as I'm a bit stuck. :)

    Cheers guys.
     
  2. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi NeilTheDruid,

    The MB3514 don 't handle the RGB outputs as the CXA1145 for which the adapter is designed. You should breadboard it as described in the MB3514 datasheet test diagram page8 (serial cap from MB pin's, then resistor to the ground).

    cheers,

    Olivier

    Edit: Well maybe the CXA1145 alike cabling should work when you have 75R termination in the scart connector. Can you post sharp a picture of your setup?
     
    Last edited: Nov 26, 2011
  3. NeilTheDruid

    NeilTheDruid

    6
    0
    Jun 21, 2011
    This is what I have so far:

    Instead of soldering to the chip directly I have soldered to points with direct continuity to the pins I need. I decided to do so because I didn't want to accidentally remove the chip from the board. This is the colour coding or my wire.

    Red - Red
    Green - Green
    Blue - Blue
    Yellow - Composite
    White - Blanking Switch voltage
    Black - Ground

    The top of the picture of the circuit I've built is the "to console" side and the bottom is the "to socket" side.
     

    Attached Files:

  4. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi NeilTheDruid,

    Wiring looks very good, I guess you remove the copper under each resistance. The circuit use the composite video signal (MB3514 pin20) as composite sync signal, not sure this will be OK on all TV's.
    The CXA1145 as a composite sync signal on pin 11 but the MB3514 not . Can you connect the SCART pin 16 to the ground via the 100R resistor to check if its' OK in composite mode?

    Olivier
     
  5. NeilTheDruid

    NeilTheDruid

    6
    0
    Jun 21, 2011
    Hi Olive2222,

    Yes I cut out the copper under the resistors. You were right about the composite pin. I moved the composite signal over to pin 19 on the scart socket and that is now working. :)

    Now I've just got to figure out what is wrong with the RGB and RGB blanking. I still think the voltages are too high. The RGB outputs are supposed to work at 0.7v each but I'm getting nearly 2v on each channel.
     
  6. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi NeilTheDruid,

    The RGB levels (as viewed by the TV)will be halved due to the two 75ohms resistors. What it can be done is to build a small sync extractor based on an lm1881 (just google a bit).

    Olivier
     
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