Genesis S-Video mod not working after two attemps.

[horror77]

I have gotten picture, just no color. I tried to switch around circuits to double check both are working and looks like both are good. So close. I just wonder what it is.



OLD Post:  Hello to all whom read this.

Yesterday and this morning I thought I would go over the schematics and suck and give this project another whirl. I didnt have the schematics last time and only crappy pictures of a board someone built so going into this the second time I felt that it must work.

So I built the circuit this time not on a board. It is just laid out like the diagram so I know it is right. The first time I connected it I got a black and white looking Sega Logo. I thought the C and Y were switched so I tried to switch them around with a dead screen as the outcome, so I switched them back. I then tried to switch around the capacitors with still no results, but this time nothing happened, so I switched them back as well. I then thought it was the 2N3904 transistor so I switched them around and nothing happened either so because i had spare ones I just replaced them with new ones.

Should I try to replace the capacitors? Does the bar on the diagram mean that the capacitor arrow is going away from it or towards it? My guess is away as the bar means regular signal that is being amplified.


I did get a black screen and a weird humming sound from my television when using a generic S-video cable. I have a converter cable that changes s-video to composite and now I get a sideways line and I can barely see the graphics but they are there. I have tried to switch the capasitors again and try switching the pin 15/16 and neither made it worst or better. Im stumped. I test the system and it still works like a champ.

Please any feedback would rock.

I have been using this guide as reference.

http://www-unix.ecs.umass.edu/~dhowland/mod/

Here is my circuit
http://s84.photobucket.com/albums/k4/horror77/?action=view&current=miserylovescompany.jpg

[kendrick]

My first guess is that you've got the polarity of the electrolytic capacitor wrong in one or both lines of the S-video output. Make sure that you've got the positive and negative sides lined up right according to the diagram you've downloaded.

[horror77]

I replaced the old transistors with 2N3904 NPN that the shack had in stock. I bought 4 cause they were cheap. So i get an image now but its very dark and rolls to the left. What am I missing?

[l_oliveira]

Since you're dealing with video signals that circuit looks quite big and can receive a lot of interference.

About S-Video, Y is a Black and white image with only the bright information for the image, hence the name "luminance"
C is only the color information for the RGB decoding so if you get a B&W image your Y circuit is working properly but the C is not.

If the image is too dark the transistor might not be amplifying properly ... Maybe you swapped collector and emitter pins around ?

I used that schematics for my S-Video mod but instead of the proposed transistor I used a BC548.
Removed the RF unit and put the S-Video connector on it's place.
It's a model 1 Mega Drive made in 1990.

[horror77]

yeah, the board is just a way to debug the mod area faster. I made a small one that never ended up working right. I have got the image to come in fine, but still black and white. I used the multimeter to check the signal at the s-vid plug and even when switching circuits completely still came to be the Y Color was 1.30volts and the C was 4 volts.  I took a reading at the wires pulling from the CXA1145 Chip and the Y=2.15 where C=2.50. Im just really trying to get some color now. Yum.. the image looks so very pretty but black and white!

any comments would be good. I tried swapping around things again like to rule out one of the circuits is done wrong with the exact same results. I tried to solder the points again but same thing. This time the tiny points were pretty hassle'ish!

So I hooked it up to my native s-vid tele and it looked good somehow. The SEGA logo in the beginning of sonic was black then the title screen was color but a pretty dark color considering the other screen shots ive seen when s-vid was used. It played in color for a round or two of the demo and then went black and white again. I notice the SEGA logo the most as I remember that from childhood.

Cheers and I wish it was working.

[albino_vulpix]

When I was modifying a Master System for s-video, I had similar problems. The image would be fine at some points, then go crazy.

I had the transistor legs wrong. Different models use different leg allocations. Look up a datasheet for the ones you're using.

[horror77]

Ah, well I tried to switch them, hoping to get color and mess up the black n white but no dice, so i switched them back. Both are the same transistors and they came with the diagram on the back of the packaging.

I am pulling from a CXA1145M chip which the diagram looks like its the same for the CXA1145P (the one he is pulling from). I'm stumped.

[Drakon]

here's an alternative that's not too expensive

I bought product a-22 from here:

http://www.arcademvs.com/ARCADE_ACESSERIOR.htm

for like 35$ shipped.  Wired it into my genesis, and wired the power into a 286 computer power supply I had sitting around, and here's the difference

top is regular composite, bottom is through the thing I bought



Did you also make sure you wired the lines into the correct legs of the video chip?  If you're getting colour sometimes then I guess you did.  I honestly don't know what else to say.

[duo_r]

ok is that basically a Jrok encoder clone? I have heard the Jrok Svideo converter don't work well with Turbo Duo/ PC Engines, would this be the same???

[Drakon]

ok is that basically a Jrok encoder clone? I have heard the Jrok Svideo converter don't work well with Turbo Duo/ PC Engines, would this be the same???

it's not a jrok at all it's just a rgbs to s-video converter board.  The circuitry on my board is completely different from jrok.  I e-mailed the jrok guys they wanted twice the price that I paid for this board.  The board I bought is actually meant to play arcade pcbs on your tv.  But the rgbs signal out of these older systems is the same type so it's fully compatible.  As for pc engines/turboduo/turbografx I don't own one so I've never tried.  I heard that you have to do a slight mod on the system to get rgbs out of it because the AV out on them doesn't support rgbs (atleast I don't think it does).  So far I've tested my board on a genesis model 2, a super famicom, and a snes model 1.  All three work perfectly.  However the snes/super famicom were a slight pain to get working.  To get them working I needed to put a capacitor in the sync line out of pin 3 otherwise the board wasn't able to get sync information from that pin.  Capacitor I'm using just came in a super famicom scart cable.  It's 100uf 10v....which is strange because all websites I checked say the snes rgb lines need 220uf capacitors.....

[duo_r]

is it CXA1645 based? Any detailed pics, the website has low res photos. Also, what does RGBS mean? Does that just mean RGB Signal because normally people just refer to as RGB.

Yes I have a modded AV port that does have RGB and also Sync available for use. I have an amp in my Duo-R so it should pretty much be good to go. I was about to buy the RGB to Component Jrok until I saw this....of course component would be a grade higher but the price is very attractive on this one. I see it ships from China, did you purchase this from the US?

ok is that basically a Jrok encoder clone? I have heard the Jrok Svideo converter don't work well with Turbo Duo/ PC Engines, would this be the same???

it's not a jrok at all it's just a rgbs to s-video converter board.  The circuitry on my board is completely different from jrok.  I e-mailed the jrok guys they wanted twice the price that I paid for this board.  The board I bought is actually meant to play arcade pcbs on your tv.  But the rgbs signal out of these older systems is the same type so it's fully compatible.  As for pc engines/turboduo/turbografx I don't own one so I've never tried.  I heard that you have to do a slight mod on the system to get rgbs out of it because the AV out on them doesn't support rgbs (atleast I don't think it does).  So far I've tested my board on a genesis model 2, a super famicom, and a snes model 1.  All three work perfectly.  However the snes/super famicom were a slight pain to get working.  To get them working I needed to put a capacitor in the sync line out of pin 3 otherwise the board wasn't able to get sync information from that pin.  Capacitor I'm using just came in a super famicom scart cable.  It's 100uf 10v....which is strange because all websites I checked say the snes rgb lines need 220uf capacitors.....

[Tiido Priimägi]

When I tried the S-vid on my MD2, I just ocnnected the Y and C signals directly to my TV, I got too bright picture... then I used a 56ohm resistor on one singla and it was fine... now put caps there and it gets more or less polite. Since I'm using RGB I had no use for the mod and removed it.

[kendrick]

Don't some MD2/Gen2 units have a different video encoder chip? I don't remember if the CXA164 produces true Y/C signals that don't need amplification, but if I remember correctly there are some drop-in replacements that are pin-compatible that do that.

[duo_r]

yes - so would this RGB board be a good solution for the non CXA encoder Sega Genesis (Most Sega 2's and all the 3's)

[Drakon]

is it CXA1645 based? Any detailed pics, the website has low res photos. Also, what does RGBS mean? Does that just mean RGB Signal because normally people just refer to as RGB.

Yes I have a modded AV port that does have RGB and also Sync available for use. I have an amp in my Duo-R so it should pretty much be good to go. I was about to buy the RGB to Component Jrok until I saw this....of course component would be a grade higher but the price is very attractive on this one. I see it ships from China, did you purchase this from the US?

uhhhhhhh nope don't think so.  There's one big chip that says BH7236AF on it

and there's two smaller identical chips that say....3 sets of numbers...not sure which is the the one you're looking for

and mine actually I believe came from canada.  Which surprised me...because it's quite the chinese product....even the instructions that came with it were pretty darn useless but it's not exactly rocket science wiring this thing up.  I got mine off of ebay but I can't find it there anymore.  Maybe they'll put it back up?  And yes...the price is ultra sexy.

oh yeah, by rgbs I just mean red green blue sync

Don't some MD2/Gen2 units have a different vi5deo encoder chip? I don't remember if the CXA164 produces true Y/C signals that don't need amplification, but if I remember correctly there are some drop-in replacements that are pin-compatible that do that.

absolutely.  And both my US model 2's have the worst one that doesn't output s-video, luckily the rgb out of them is just fine.  So I just did external encoding instead.  I also picked up a japanese megadrive model 1 today but there's NO way in hell I'm taking that apart unless I have to.  And yes, it works with my rgb to s-video encoder like a charm.

yes - so would this RGB board be a good solution for the non CXA encoder Sega Genesis (Most Sega 2's and all the 3's)

yup.  The above screenshot was taken with a genesis using basically the worst model built in encoder chip I could find.  Heck this board so far has been perfect for anything that pumps out a rgb signal.  Excluding the suffering of having to move the capacitor on my snes scart cable from a colour line over to the sync line to get it working on the snes.  Honestly I think it makes more sense to get one of these considering how cheap it is.  Here's some more screenshots of it in action with my genesis model 2 using the all time terrible samsung KA2195D chip





but hey, if you want to complete the mod for the fun of the challenge then go right ahead.  I enjoyed the challenge of wiring all my crap up through some sort of bizarre scart rig so I could easily switch which system uses the encoder (since I only play one system at a time).

[duo_r]

Ok a friend of mine tried one of these and they said the video quality paled in comparison of the jrok encoder. Lots of color bleeding.

[Drakon]

Ok a friend of mine tried one of these and they said the video quality paled in comparison of the jrok encoder. Lots of color bleeding.

well it's good enough for me.  As for "color bleeding" it's s-video...I don't think it's possible to avoid that with s-video.  But for the sake of 16-bit gaming the picture it pumps out is definitely good enough for me.  Obviously if my tv had a component input I would have gone with jrok.....they're the only guys I found making rgb to component boards.  Still for ANY system that pumps out a rgb signal it makes more sense to me to get an external encoder.  Just for the fact that it can be used on all these systems without any modification (usually).

[Tiido Priimägi]

S-vid still has oversaturated colors, but its much less blurry than composhit.

My MD2 uses a Fujitsu(?) MBxxxx chip BTW, its composhit is worse than the KA2195 chip, but S-vid looks nicer than from pics above. RGB nice and clean on all, so no worries with that.

[Drakon]

S-vid still has oversaturated colors, but its much less blurry than composhit.

My MD2 uses a Fujitsu(?) MBxxxx chip BTW, its composhit is worse than the KA2195 chip, but S-vid looks nicer than from pics above. RGB nice and clean on all, so no worries with that.

the above pics don't look nearly as good as it looks on my tv

[Tiido Priimägi]

your pics have oversaturation problem (at least in my eyes).

[Drakon]

your pics have oversaturation problem (at least in my eyes).

yeah but I can fix that by turning down the "color" setting on my tv

[horror77]

im just still without my mod working correctly. I have no other thoughts on how to get it working right. Thanks for the hijacking btw. Im doing this so I dont have to buy some kind of board to just solder to the pins and 5+V and ground. Thanks anyways and officially stumped.

[horror77]

ok, decided to just install the same circuits to another system and same problem. I just replaced the transistors but can replace them again. I just really really really want to get this thing done and have beautiful color. i switched pins on the transistor and it just acted the same way. I pulled the c pin off and it was struggling but the black and whiteness was still there.

Time to analyze everything once again. dont know what is wrong. probably rewire the whole thing tomorrow.

[horror77]

rewired it to the exact diagram this time and still not a drop of color. I must just be pulling from the wrong damn pins. Im done with this mod. over all i dropped about 10 hours on it and for what..
blah

[albino_vulpix]

Do you have any more pictures of your work? Could be something you're missing that someone else might pick up.

[l_oliveira]

I don't think you should give up ... I just think that video signals are a bit troublesome and since the chroma carrier is on the megahertz range that circuit would work it's best if it's small.

[horror77]

yeah. I will redo it with new parts and hope it works correctly this time. I thought I got it wrong and tried connecting pins 21 and 22 thinking they counted it some other way. I really do think now it was the pins as when I switched them around and got the same results, didnt seem like my circuit was faulty. I am working on a CXA1145M chip. The first system I tried it with actually just fried out yesterday. I think this was just cause of my carelessness and frustration with the project. I will take some pictures of it soon. Thanks for responding.

[Drakon]

rewired it to the exact diagram this time and still not a drop of color. I must just be pulling from the wrong damn pins. Im done with this mod. over all i dropped about 10 hours on it and for what..
blah

10 hours is nothing.  I've spent countless nights farting around with stuff like that....but that's just because I enjoy it.  Anyway I fixed my oversaturation problem.  It's correct my board had oversaturated colours.  This could be fixed by turning down the "color" setting on my tv but then everything else looked colourless.  So I just installed 3 resistors on the colour wire of my s-video cable from the board....now it's beautiful.  As for the refresh effect I notice it...but again only from right infront of the screen.  When sitting at normal distance from the tv you don't see it.

[horror77]

oh I understand 10 hours is nothing for modding but I thought I have done this right 2 times already. Its frustrating and goofy but I will get it done.

Im sure it would take a lot longer without this sites feedback so thanks again.

[Drakon]

oh I understand 10 hours is nothing for modding but I thought I have done this right 2 times already. Its frustrating and goofy but I will get it done.

Im sure it would take a lot longer without this sites feedback so thanks again.

I wish I could help but maybe you could supply us with a clearer picture of your circuit?  The mod has apparently worked for many people here so I'm assuming unless there's something wrong with your system then the circuit is wrong somewhere.

[albino_vulpix]

Taking a different angle here: do other s-video devices work on this TV? Could your cable be faulty?

[l_oliveira]

did you try "mixing" both outputs from your Y/C buffers into the TV composite input for testing ?

[Tiido Priimägi]

Some TVs require to be manually put into "S-vid mode"... my TV has S-vid and Composhit inputs on front, but you have to manually set it to use either from the menu... otherwise its black and white...

[Drakon]

Some TVs require to be manually put into "S-vid mode"... my TV has S-vid and Composhit inputs on front, but you have to manually set it to use either from the menu... otherwise its black and white...

if this guy didn't test his s-video connection first I'm gonna laugh so hard

[Tiido Priimägi]

You can't laugh in this case. I just hooked up 2 wires on 2 pins on the RGB encoder, one wire had a 56ohm resistor in series, then the ends of the wires went into my TVs S-vid input. I had to press the menu button 14 times, and press the + to put it in S/vid mode to have colors... if I'd press - it will assume it gets composhit and have black and white image. Simple... http://www.hot.ee/tmeeco/MYSMD2.JPG (I guess you won't notice I've done anything with the RGB encoder...)

[horror77]

yeah I have tried other systems using S-Video through my tele like my 3do so I know that works. I will try it again but here is to soldering. I think I will attempt this again very soon. Thanks for all the info.

[XianXi]

Old thread I know.

I just tried this mod using the same schematic and have double and triple checked my circuit and it's exact so I don't know why I get no picture at all. Switch Chroma and Luma lines on the jack and rewired the ground. Checked continuity even rebuilt the circuit fresh.

Is there any errors in the schematic by chance? Just to confirm the elec caps have the negative leg going to the Y orC input and positive goes to B, correct? I noticed on the encoder chip underside that the Y and C lines go into a series of resistors, are these needed or can I remove them?

At least I know the stereo mod is working.

[XianXi]

Ok I fixed it, I was using NTE85 transistors which had a different pinout from the one on the site. Works now but it looks like the genny has some dirty sync so I am putting in a sync cleaner.


Edit: Just installed the Sync cleaner and it didn't change anything, using a JROK sync cleaner btw. Picture still looks the same so I'm guessing it's the combo of the 100uf and 33ohm on the Chroma line since it looks over saturated, a 75ohm should be better.

[Artemio]

What are the negative effects you are seeing? I had some problems with Sync on teh Genny, though using RGB out. I fixed them with an LM1991 but they were very specific. I was loosing the signal every now and then in certain games, for example Sonic CD. it was on specific parts that increased the general brightness.

[XianXi]

Just changed it to a 82ohm since I didn't have a 75ohm res. So now the picture looks better but there is still some color bleeding. I hope it's not normal cause it looks awful. I notice it most while playing Stider II on the 2nd stage where the sky is purple. Instead of a 100uf should I use a 470uf or 220uf coupled with a 75ohm?