Genesis S-Video mod question (CXA1145)

[Sensato]

Simply put, aside from the NTE85, which transistor(s) can be used for the S-Video mod on a CXA1145?


Full Story:

I'm actually trying to mod a Sega Genesis for S-Vid output. Tried pulling the signal using a 220uF capacitor and 75 Ohms resistor from leg 15 and 16 of the video encoder chip. Althought it looks quite sharper than the actual composite signal the A/V connector outputs, the screens flikers and shakes when the screen is mostly white (like the white screen SEGA logo on Sonic 2).

Now I hear that this 220uF and 75 Ohms is not the mod to perform on this CXA1145. You need to build a small (current?) amp circuit in order to get accurate S-Video. Is that so? Tried the mod shown on Neostore.com with a cheap 2N3904 (that's the only NPN I had in hand) and didn't get anything good. Well, it looks relatively close to the original signal (on a scope) but doesn't display properly (or at all should I say) on-screen.

So, yeah, any replacement for the NTE85? If I'm lucky, might have what it takes in stock. I just don't especially feel like shopping online for 2 transistors. Thanks in advance!

[viletim!]

The NTE85 is just a general purpose NPN transistor, nothing special at all. Your 2n3904 would be a suitable replacement for it.

[Segasonicfan]

Just would like to say I have actually done this mode with a 2N3904 and it works perfectly.  You should check my site for the best schematic on the mod too (in the CDX section at the bottom).

Just make sure you get the appropriate C,B,an E pins connected properly.

-Segasonicfan

[Sensato]

Just would like to say I have actually done this mode with a 2N3904 and it works perfectly.  You should check my site for the best schematic on the mod too (in the CDX section at the bottom).

Just make sure you get the appropriate C,B,an E pins connected properly.

-Segasonicfan

Don't know how I could have mistaken the pins on the 3904 but I did!

I still have a few adjustements/tests the make but so far, the signal I'm getting isn't perfect. Colors appear slightly off and bland, there seems to be some bleeding too and the screen is filled with vertical lines. Pulling the signal through a 75 ohms and a 220uF seems to look better (aside form the white screens whichs shakes with RC mod).

Now that I'm thinking about it, is it better to lift pins 15, 16 form the board or it isn't necessary? I wouldn't hesitate to fiddle with that if I had a spare Genesis PCB which used the 1145 but what I have left uses S KA...

Thanks for the help!

[Segasonicfan]

don't lift the pins-it's not necessary at all.  Did you use the schematic from my site?  It has the proper resistance values (33ohms output).  I've had perfect success modding Genny systems with it.

-Segasonicfan

[Sensato]

The mod works great indeed. The main problem I faced was that I was conducting my tests with poor wire connections/joints (mostly used alligator clips, some of which are pretty worn out).

Thanks a lot for the help, that kept me motivated when I needed it and  I can now enjoy one of my fav system with a much better display. If I could have an RGB capable monitor, that would be even better but I'll stick with S-Video for now.