Sega Master System S-Video mod

[channelmaniac]

OK,

I have an early 1st Gen SMS with the Sony V7040 video encoder and I wanted to add an S-Video and audio jacks to it. It's been a PITA trying to track down the data so I thought I'd share.

The data sheet can be found out on www.datasheetarchive.com and it does have a different pinout than the typical CXA-1145 encoder.

I found this simple amp on the SMS Power! forum and modified it to use pots instead of fixed resistors.


. | +5v
. |
. |
.video | / c
.in ---|<
. | \ e
. NPN | 27 video
. +--RRR--- out

Instead of a 2N3904 I used some generic pair of NPN transistors and they worked fine.

The pins to tap on the encoder chip are 14 for Y and 13 for C. Build 2 amps on one small piece of perfboard and use one for Y and the other for C.

Tap pin 1 on the A/V jack for audio. This can be done from the top by soldering to the side of the exposed leg.

+5v can be tapped off the diode next to the CPU. Ground can be tapped anywhere. Cut the section of the RF shield off at the back, but not all the way up to the 90 degree bend... Leave about 1/8" hanging down so you can fold that under, flat against the top to keep it from cutting the wires.

Reassemble and enjoy!

Before: (RF output fed through VCR then out composite to Sony HD LCD monitor)

http://farm3.static.flickr.com/2702/4394465794_c652bcc949.jpg
http://farm5.static.flickr.com/4017/4394465646_96d177525a.jpg
http://farm5.static.flickr.com/4034/4393698555_9cc99eaf16.jpg

After: (S-Video output fed directly to Sony HD LCD monitor)

http://farm5.static.flickr.com/4048/4394466258_4b65082f58.jpg
http://farm5.static.flickr.com/4047/4393699085_d4eff34de4.jpg
http://farm5.static.flickr.com/4020/4393698965_6c3b9b523a.jpg

[electrochip]

SMS brings back so many memories, great job. I'm sure many people will find this info useful.

[Logicdustbin]

here is a nice picture on a plasma TV :D


http://img.photobucket.com/albums/v246/Logicdustbin/DSC00179.jpg

[LimeiBook86]

Wow excellent work, the difference in picture quality is night and day! :)

[channelmaniac]

Thanks!

I saw plenty of mods for the version with the Sony CXA-1145 encoder but couldn't find jack for the V7040 version so I thought I'd share with everyone.

RJ

[weirdguy]

The amp is almost the same as the one for the Sony encoder.

I love datasheetarchive.com. They really got data sheets on any existing chip.

[channelmaniac]

Modified a 2nd unit tonight... This one has the CXA1145 encoder and gives some jailbars on the screen. They are minimized by playing with the resistor rating.

Lum: 27 ohm
Chr: 220 ohm

When the resistor on the Chroma line is set to 330 ohms my Sony HD LCD Monitor will intermittently lose color. Lowering it to 220 gives a great picture.

[BigBoogie2]

Have an origianl Master System (V7040). Worked great. Jailbars are quite bad.

I've got a 27ohm on the lum, and 75 on the chr. You mentioned changing the resistor may help.
Which direction are you changing it, and what work best?
Anyone else play around with the resistor settings with good results?

[MaxWar]

Have an origianl Master System (V7040). Worked great. Jailbars are quite bad.

I've got a 27ohm on the lum, and 75 on the chr. You mentioned changing the resistor may help.
Which direction are you changing it, and what work best?
Anyone else play around with the resistor settings with good results?

The jailbars will decrease as you put more resistance on chroma. However, the picture also becomes noisier.
So its a trade off.
In my experience using 220ohm on chroma as previous poster suggested would result in visible noise.
What I do Is typically use a Trimpot of 100 ohm and tune the value to get the best compromise between noise and jailbar.
If you want more resistance than 100 ohms, just add a resistor in series. You could also use a 200 ohm precision trimpot i guess.

[BigBoogie2]

Thanks

No Trimpot. slowly increased to 150. still not great. decided to try a 220 just to see. There was visible noise in some colors, and almost no improvement in jailbars. Truthfully the jump from 75 to 150 is not that noticeable either, but I guess I'll have to live with it. Is there always going to be bars in sms, or should I try looking for another model/chip?

[ApolloBoy]

Thanks

No Trimpot. slowly increased to 150. still not great. decided to try a 220 just to see. There was visible noise in some colors, and almost no improvement in jailbars. Truthfully the jump from 75 to 150 is not that noticeable either, but I guess I'll have to live with it. Is there always going to be bars in sms, or should I try looking for another model/chip?
Ditch the transistor on the chroma signal and replace it with a 220 uF capacitor. You'll still want the resistor though, you can try either 220 ohm or 330 ohm which should give you a relatively jailbar-free image without too much noise.