Help with video encoder!

[villahed94]

I'mdesigning an external encoder. It uses the RGB+sync+ 5V signals which go out of the DIN connector. I´m using the MC1377 encoder, which provides a far superior video quality than the internal CXA1145 the Genesis uses.
But I'm having a problem. I've been able to sync the Luma after using this schematic:
http://atari.8bitchip.info/stvid/stencoder.png

The capacitors used in the RGB inputs are 15uf as specified in the datasheet.
In pin 9 a 2sc1740 transistor is used to amplify the Luma signal.But this is the problem.

(click links to see the pictures, too big to embed)
http://img40.imageshack.us/img40/953/dscf0825f.jpg
http://img818.imageshack.us/img818/6051/dscf0835o.jpg

The Luma is too dark. I have tried with and without the capacitors/transistors. No resistors have been put in the RGB inputs, not even to ground. Something that must be noticed is that if the 33uf capacitor is put before the transistor, I get no Image. I'm desperated and bordering craziness. Please help me to finish that project. Any help is highly appreciated.

[Robivy64]

It looks like you aren't getting ANY luma signal. Perhaps you need a 1Vpp RGB input signal. The AV jack only provides 0.7Vpp.

[Guntz]

Looks like he ain't getting any chroma either. I've looked at the datasheet and encoder calls for a very archaic Chroma amp. Here's a link for anyone interested:

http://www.datasheetcatalog.org/data...a/MC1377DW.pdf

[Drakon]

that's luma without chroma. And something is wired wrong because you're getting blurring. Did you remember to wire the 12v as well?

[villahed94]

Yes I did. Using a converter IC.

[Drakon]

test the encoder circuit on some other rgb system and see if it works right?

[Chilly Willy]

I made an encoder using this same chip for my Amiga 500. I used potentiometers in place of the two resistors on the RGB input lines. That allowed me to adjust the level of the inputs to the encoder.

[villahed94]

Usually which is the input level of the Genesis?

[Chilly Willy]

Usually which is the input level of the Genesis?

Not sure who you're asking, but I have no idea, but using a pot would allow you to adjust the levels in case the lines are lower than the circuit requires. When I made my A500 encoder, I started with the pots set to half, and adjusted them until I got a good picture.

[villahed94]

Not input levels. Output levels. IIRC the MC1377 requires 1.0 vpp for 100% sat image.
BTW when I was fiddling today with the circuit I got a nice luma.I was going to hot glue it, but i moved the connection and it´s back to the problem. Problem is: I dunno which was touching each other that caused a solution. Need to check out.