SMS S-VIDEO MOD ISSUE - HELP PLEASE!

Hi everybody,

I just tried a s-video mod on my master system pal model 1 to test the s-video quality on my commodore 1084s monitor which get chroma and luma trhough 2 rca plugs, , I soldered every wire from pin 15 and 16 of cxa to a 75 ohm resistance and a 220 uf capacitor, as I see in some mod tutorials, paying attention in polarity ecc.

Picture seem ok but white color is mixed with yellow color somewhere, where it should be only white, like in the 'master system" opening screen.

want to know if I did something wrong, maybe you can suggest me better resistance or capacitor for one wire or another...later I'll check the soldering to see if the problem starts there.

many thanks for the attention!

 

The luma signal needs to be amplified on the CXA1145 in order to be useable. To do that, take a 2N3904 transistor, wire up the base to the luma pin on the encoder, connect the collector to 5V, and then solder a 33 ohm resistor on the emitter. From the other end of the resistor is your final luma output. I'd also suggest using a 220 or 330 ohm resistor on chroma instead of 75 ohm, as it reduces the jailbars you normally get with S-video on the CXA1145.

 

Many thanks for the quick reply and the detailed answer, imma try it for sure but first I need to find the components
220 uf capacitor remains on the chroma wire?

For normal video pin 20 of cxa is ok 220 uf + 75 ohm? I modified that way a sms2 and it looks fine on my trinitron crt and a little too much colourful on my 1084s but ok

thanks again

 

Yes.

If you find that the video's too bright you can bump up the resistance a little to 120 or 150 ohms.

 

thank you man, wonder how sega machines look via s-video in my 1084s have to try also with mega drive even if I doubt will be better than rgb which is perfect to me (after have lift pin 6 of cxa)
I m pretty sure that having 6 pin lifted make impossible to get s video, wonder if is possible to put a switch on pin 6 to alternate rgb and s-video/composite

 

I don't know if it was bad soldering (I had to resolder one capacitor) or if I put chroma and luma inputs, but second time I tried the connection with 75 ohm and 220 uf picture was better than my first attempt and indeed, good.

I still see some strange yellow blurs in the "master system" white writing in opening screen and the jailbars are heavy, especially for blue color, but not worst than rgb jailbars.

Surely I'll try with your set up to see the results, anyway I did some photos to show how it looks.

sms is the only machine I could see in full color in 60hz mode without using rgb....great....think it output pal 60?

View attachment Foto0102.jpg

View attachment Foto0095.jpg

 

Looks pretty good! Nice work.

 

I just tried this mod using c546b transistor instead of 2n3904 (can't find them and shopkeeper says that are identical) and got the same result of 75 ohm + 220 uf, maybe the jailbars are less visible but really cant bet on it..330 ohm seem to be less colorful than 220 ohm but again I cant say that for sure, I would have two monitors and two consoles to make comparisons
I also made photos, but trust me, they look identical to the first ones made with 75 ohm + 220 uf

thanks anyway for the tip, I think I'll keep this last mod