Adding RGB scart to a Sega Master System.

[NeilTheDruid]

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.

 

[OLIVE2222]

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?

 

[NeilTheDruid]

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.

 

[OLIVE2222]

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

 

[NeilTheDruid]

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.

 

[OLIVE2222]

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