Genesis Model 1 no video output[fixed] Help with S-Video!

[APE992]

Which circuit did you use for S-Video? I recently installed S-Video into a JVC X'EYE initially using this design:
http://www.jamma-nation-x.com/jammax/genesismods.html

It looked great on my personal Sony Trinitron but once the owner got it back he found the colors would fluctuate between too bright and too dark IIRC; thing is he too used a Sony Trinitron but a different model. I replaced it with this design:

http://gamesx.com/wiki/doku.php?id=a..._1_s-video_mod

Bit more complicated but looks just as good. He found it to work perfectly with his Trinitron as well as several others I tested it on. Not exactly sure why the simpler circuit didn't work across the board.

[Ricky]

Which circuit did you use for S-Video? I recently installed S-Video into a JVC X'EYE initially using this design:
http://www.jamma-nation-x.com/jammax/genesismods.html

It looked great on my personal Sony Trinitron but once the owner got it back he found the colors would fluctuate between too bright and too dark IIRC; thing is he too used a Sony Trinitron but a different model. I replaced it with this design:

http://gamesx.com/wiki/doku.php?id=a..._1_s-video_mod

Bit more complicated but looks just as good. He found it to work perfectly with his Trinitron as well as several others I tested it on. Not exactly sure why the simpler circuit didn't work across the board.

for the luma circuit I used a 2n3904 npn and a 33ohm resistor at the emitter end out to the socket.
I took the +5v straight from the CXA1156P and obviously luma for the base.
For the chroma however I had to do a lot of f'ing about to get it perfect. I soldered a bunch of resistors in series, I think I remember the values.

it goes like this
[C out] -> [220uf cap] -> [33ohm res + 68ohm res + 68ohm res + 220ohm res + 220ohm res] -> out to s-video

Yeah.. it took a lot of messing around for me to get it perfect and who knows it might not even look as good on another tv.. I got to test that
I'm playing on a flat screen sharp, looks amazingly good. I'll try another tv later.

[jb143]

Not exactly sure why the simpler circuit didn't work across the board.

That first circuit just seems way too simple...for video especially. The second schematic utilizes feedback which will help with the amplifiers stability. Without it the gain can fluctuate slightly which would explain the brightness fluctuations you mention. My guess as to why different TVs behave differently is that different TVs could have circuits in place to help with such fluctuations.

[DogP]

That first circuit just seems way too simple...for video especially. The second schematic utilizes feedback which will help with the amplifiers stability. Without it the gain can fluctuate slightly which would explain the brightness fluctuations you mention. My guess as to why different TVs behave differently is that different TVs could have circuits in place to help with such fluctuations.

I don't see any feedback in either of those circuits. Both of them are essentially the same circuit... an emitter follower amplifier, which has near unity gain. The difference on the second circuit is the AC coupling of the input (why they used two caps, I'm not sure), the bias on the input (since they AC coupled it), and a termination resistor on the output.

IMO, the AC coupling and biasing is completely pointless, since the amplifier works from (about) 0V-5V, and the signal is completely in that range. The termination resistor is a good idea to act as a pull-down, as it limits the dependence of the termination at the TV. Is that really a 110_k_ ohm though? That seems WAY too high to be of any use. To me, it looks like whoever made that circuit started with the first circuit, then added some components and played around with values until they got something to work on their TV, then posted that schem.

DogP

[omp!]

I don't see any feedback in either of those circuits. Both of them are essentially the same circuit... an emitter follower amplifier, which has near unity gain. The difference on the second circuit is the AC coupling of the input (why they used two caps, I'm not sure), the bias on the input (since they AC coupled it), and a termination resistor on the output.

IMO, the AC coupling and biasing is completely pointless, since the amplifier works from (about) 0V-5V, and the signal is completely in that range. The termination resistor is a good idea to act as a pull-down, as it limits the dependence of the termination at the TV. Is that really a 110_k_ ohm though? That seems WAY too high to be of any use. To me, it looks like whoever made that circuit started with the first circuit, then added some components and played around with values until they got something to work on their TV, then posted that schem.

DogP

You're not the first to say similar
http://www.smspower.org/forums/viewt...ght=transistor

[APE992]

I can tell you from experience that viletim!'s circuit worked on my Trinitron but not the second Trinitron.

Maybe the second one has a poor design or something is failing, no idea. Perhaps the extra components are useless and serve no function - not far enough along in my EE studies to be certain though what I'm reading from the last two posts I'd have to agree with.

[jb143]

I don't see any feedback in either of those circuits.

Heh...it looks like you're right. I just did a quick glance and didn't pay much attention to where that resistor network was actually attached. But still, that first circuit looks too...textbook. Like something used to demonstrate basic amplifier design but not something you would actually use. A nice op-amp circuit(with negative feedback ) would probably work wonders though.

[DogP]

Heh...it looks like you're right. I just did a quick glance and didn't pay much attention to where that resistor network was actually attached. But still, that first circuit looks too...textbook. Like something used to demonstrate basic amplifier design but not something you would actually use. A nice op-amp circuit(with negative feedback ) would probably work wonders though.

Actually, it works quite well in a lot of applications, though I do like to add a termination resistor sometimes. I just used it the other day to basically act as a horizontal sync buffer for a VGA output. I was getting a loss of h-sync from a VGA output on one of my arcade games to a Plasma monitor, so I tossed an emitter follower circuit in line with the h-sync, and it worked great. I did terminate it with a 220 ohm resistor because the slew rate of the falling edges was a little slow, causing a slight jitter on the screen.

But yes, a good op-amp circuit is nice as well, though this simple transistor circuit certainly has its uses.

DogP

[jb143]

I did terminate it with a 220 ohm resistor because the slew rate of the falling edges was a little slow, causing a slight jitter on the screen.

But yes, a good op-amp circuit is nice as well, though this simple transistor circuit certainly has its uses.

You know, I was actually looking up specs on the transistors being used to see if a too low slew rate could be causing people issues. I know from experience that the same exact part number from different manufacturers can have different slew rates. This was for op-amps though. Transistors don't list it, I guess because it has more to do with the final amp design. You would probably need an oscilloscope to figure out what it is though.

If anyone is wondering, slew rate has to do with how an amplifier handles quick changes. If an amp has a low slew rate then a fast changing signal can get distorted. In video applications you typically want a higher slew rate. Same for bandwidth but the general purpose transistors look to be high enough.

I guess I'm just a bit leery of using general purpose transistors in a very simple circuit for video applications. But hey, if it works it works. But since people have been having issues between different TV's, and the instructions basically say randomly use different values for the parts until it does work, then I'd say a better alternative would certainly be nice.

[APE992]

A higher slew rate would be nice though the transistors I used seem to handle themselves just fine. At least I don't notice any problems but that doesn't mean my display isn't hiding them. After doing some calibrations I found it was losing about 2" worth of picture to overscan on all four sides. Likely normal but it doesn't please me.