Dreamcast Internal VGA modification

[MrComputerRevo]

Hey! Can somebody show underneath of board with capacitors? I am confused where to solder wires....

[segadreamsat]

Hello !
I've done this VGA Mod, but I'm disappointed with the result :
the image is steady, with the good colors, but has some kind of interference. It looks like those colors fade gradually to the right, as you can see on the picture.
Do you know where it could come from ?
I used wires from a SATA ribbon cable, so those wires are very thin and stuck together, I don't know if it could be the reason...

[jinn]

I tried the mod a few years back and it seem to be a PAL DC mod. I tried it on my US DC and it wouldn't work, then I tried to hook up the MoBo points straight to the D-Sub and it work first time. My mod did not need the
2 x Diodes
2 x 4700 ohm resistor
2 x 150 ohm resistor
3 x 220uF capacitors

[APE]

VGA is analog so it is extremely susceptible to interference. If you just used the wires one after another in a row (think ribbon cables) without grounding a wire in between each of the wires carrying a signal (ABCDE - B and D would be grounded where A, C and E are carrying an analog signal) it could introduce crosstalk but I can't tell you exactly what it looks like as I've never seen it on a VGA display before. Nor have I actually seen that particular problem before.

I'd make sure everything is properly grounded and shielded. I'd also check into how large a gauge wire you should be using for this. Wires from a SATA cable might be too high a gauge for this for all I know.

[segadreamsat]

Thank you all for your help ! With your advice, I applied several changes, and it finally works well !

Here is what I did, if it can help someone :

- I used a stripboard with pre-linked slots as shown in the tutorial (instead of my 1st board where all the slots were separated) -> less solder/wires
- I used much bigger wires between the stripboard and the VGA socket (instead of my IDE ribbon cable (yes, IDE and not SATA as I said before, it was a mistake))
- I still used IDE ribbon cable between the motherboard and the stripboard (much easier to solder to the motherboard), but this time, I took 13 wires, and used only 7 of them, leaving a "useless" wire between 2 "useful" wires (if you prefer, if they were numbered from 1 to 13, I used only the odd ones).

Thanks again !

[Calpis]

What you were seeing is ghosting from signal ringing from improper termination. Perhaps the cable was long? Or it could have been the mismatching of the cable's characteristic impedance.

[segadreamsat]

I don't know exactly where it came from. I don't think it was related to the length of cables or wires as I used exactly the same VGA cable and more or less the same length for wires for my 2 trials. Actually I think they are a bit longer this 2nd time, but not much (1cm or 2).

I also noticed that the colors are a little "darker" using VGA than using original RGB output. I guess it's normal as I saw the same thing comparing HDMI and VGA on a X360. Do you know why this happens ? Can we change this, maybe by using different capacitors ?

Once again : thanks !

[ArgyleEyes]

im just gonna ask here for randomness and lazyness not to post a new thread....so yeah sorry if need be...

in short i killed my dreamcast being foolish and not keeping track of screws...(*cocky*)
if you know what about im talking about then yeah...im wondering if i could possibly make a fix by doing a vga mod even though the video got screwed...literally...least the sd card mod worked XD

..new dreamcasts are like $50 here at the "gamer pawn store" T_T *sigh*

as for above just to add you could always test other caps or add pots to the whole process i think to get fine tuning out of it?

[DCCharlie]

I hate to bring an old thread to life but I did this mod, but I got the weirdest issue. My picture shows in Grey scale only on my monitor. I've tried 3 different monitors and they are all grey scale. I tried a second VGA connector, with the same results. I do not currently have the proper Dreamcast can=bles to verify the system was displaying in color but I have read this will usually work or not work, nothing in between.

[RedDragunee]

That sounds really odd. Have you tried checking all connections, components etc. to see if they're all placed correctly, and soldered properly? Are the components exactly the same as listed in the tutorial? Are they used, or brand new?
Have you tried a different VGA-cable, just to make sure?

[DCCharlie]

That sounds really odd. Have you tried checking all connections, components etc. to see if they're all placed correctly, and soldered properly? Are the components exactly the same as listed in the tutorial? Are they used, or brand new?
Have you tried a different VGA-cable, just to make sure?

Oddly enough, I located a random post on a random website that the guy mentioned he has an American DC and he didn't need the PCB. So for the heck of it I tried it and it worked! All color! Go figure I guess.

[RedDragunee]

Good to hear :)

[SnoopKatt]

Nice! One more thing to add to my project list :p

[simbin]

With racketboy and others gouging people for cables, I was wondering if anyone has successfully made their own? I'm not so great with a soldering iron and dremel, so I'd rather try making a cable instead of preforming surgery on my Dreamcast.

[APE]

With racketboy and others gouging people for cables, I was wondering if anyone has successfully made their own? I'm not so great with a soldering iron and dremel, so I'd rather try making a cable instead of preforming surgery on my Dreamcast.

Where are you going to get the connector? SCART cables don't have all of the wires necessary for VGA as far as I'm aware and you can't cannibalize composite cables.

[synrgy87]

a vga cable off an old crt monitor or even a new one, the actual dreamcast connector would be the only problem. maybe a DC RGB scart cable just using the connector i think they have all the pins? could be wrong though.

[APE]

a vga cable off an old crt monitor or even a new one, the actual dreamcast connector would be the only problem. maybe a DC RGB scart cable just using the connector i think they have all the pins? could be wrong though.

VGA is RGB, H-SYNC, V-SYNC, +5, GND. All but the two sync signals are available on the SCART connector unless they wired everything in there for no apparent reason. On top of that you need to have a switch to engage VGA mode which requires an additional pin very likely not wired into the SCART connector.

[synrgy87]

VGA is RGB, H-SYNC, V-SYNC, +5, GND. All but the two sync signals are available on the SCART connector unless they wired everything in there for no apparent reason. On top of that you need to have a switch to engage VGA mode which requires an additional pin very likely not wired into the SCART connector.

i simply meant using the DC side of the scart cable if all the pins are in the connector then wuld just need to be connected and a switch added in-line

[-=FamilyGuy=-]

I’m planning to make a smt version of this + scanline, and I have a few questions.
Is 1/8 W enought for the 4.7k ohm resistor? (I’m not sure)
Is 1/4 W enought for the 150 ohm resistor? (I think so)
Is 25V enought for the 220 uf capacitor? (I think so)
Shouldn’t there be a 0.1 uf ceramic capacitor in parallel with the 220 uf one?

Talking about this schematic from mmmonkey:



Thank you!

[bertmansk]

Seeing as a couple people have mentioned they eliminated the PCB for American DC's, I'm wondering what they did for the +5v for the H & V sync. Just jump them, or put a switch...?