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  • Joined: 22 Aug 2007
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SMS RGB MOD
Post Posted: Fri Dec 28, 2007 5:03 pm
How would i go about installing an RGB modification on my SMS II??

Thanks

twr198
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Post Posted: Fri Dec 28, 2007 5:21 pm
1. Search the forums, I tried "rgb mod".
2. http://www.mikeg2.freeserve.co.uk/masterful/rgb.html
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  • Joined: 31 Oct 2007
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Post Posted: Sat Dec 29, 2007 6:07 pm
you can leave the capacitors out in that mod...
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Post Posted: Sun Dec 30, 2007 5:13 am
TmEE wrote
you can leave the capacitors out in that mod...


...but you really shouldn't. They're there for a reason.
 
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Post Posted: Sun Dec 30, 2007 8:36 am
I'm assuming the composite video and audio outputs are your standard A/V ports?

If so I shall attempt that mod since none of the TVs I own have either RGB, Scart or S-Video.
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Post Posted: Sun Dec 30, 2007 6:26 pm
viletim! wrote
...but you really shouldn't. They're there for a reason.


What reason ? If I put them into my MD I get slighlty worse picture...
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Post Posted: Sun Jan 06, 2008 4:16 am
It's required by the driver circuit inside the chip. Each video pin has to drive a 150 ohm load at 1.4Vpp (at peak white) and to do this without wasting too much power it uses a class AB output stage, a bit like an audio amplifier. The chip is powered from a sinlge +5v line so the output stage is biased at Vref (about 2 volts) and the signal swings above that. You end up with a 1.4Vpp AC signal sitting on top of 2 volts of DC. Passing the signal through a coupling capacitor will block this extra bias voltage and let the AC signal pass right through.

I haven't checked myself but I presume that directy loading the output would cause distortion in the AC signal. The datasheet for the CXA1645 (the successor to the '1145) mentions:

9. Driving COUT (pin 15), YOUT (Pin 16), CVOUT
(Pin 20), and B.G.R OUT (pins 21, 22 and 23)
outputs. In Pin Description, "Capable of driving a
75 load" means that the pin can drive a capacitor
+75+75 load shown in the figure below. In other
words, the pin is capable of driving a 150 load in
AC.

.    |     75    +| |220µ
. pin|---/\/\/----| |----+
.    |            | |    |
.    |                   |
.    |            75     |
.    |      +---/\/\/----+
.    |      |
.          ---GND
         
Keep in mind that the pin is incapable of driving a
150 load in DC load in DC direct coupling.


I think you are being a bit subjective when you say that introducing the
caps makes the picture 'worse'.
 
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Post Posted: Sun Jan 06, 2008 2:49 pm
ah ok, I'll use as little components while keeping things working... and my TV already has these capacitors in it...
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Post Posted: Fri Jan 11, 2008 10:01 am
djbass wrote
I'm assuming the composite video and audio outputs are your standard A/V ports?

If so I shall attempt that mod since none of the TVs I own have either RGB, Scart or S-Video.


I never really got a response to the above?

Cause I'd be interested in doing this mod if I could get A/V outputs from the SMS2.
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Post Posted: Fri Jan 11, 2008 10:31 am
Yes, composite video is connected to the AV input yellow plug. Audio is the white plug. I've done this mod using this type of connection and it works well.
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Post Posted: Fri Jan 11, 2008 11:44 am
It has to be said: composite sucks. It's well worth getting RGB if you can.
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Post Posted: Fri Jan 11, 2008 1:54 pm
Maxim wrote
It has to be said: composite sucks. It's well worth getting RGB if you can.


Composite has served me well for over 20 years and will do for my purposes.

Unlike in Europe/UK Scart/RGB is not the norm except on thousands of dollars TV sets, and even if I did find a cheap TV with such a connection the added picture quality would be negligable due to the lower quality of the TV set.
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Post Posted: Sat Jan 12, 2008 12:18 pm
djbass wrote
Maxim wrote
It has to be said: composite sucks. It's well worth getting RGB if you can.


Composite has served me well for over 20 years and will do for my purposes.

Unlike in Europe/UK Scart/RGB is not the norm except on thousands of dollars TV sets, and even if I did find a cheap TV with such a connection the added picture quality would be negligable due to the lower quality of the TV set.


That's true, just the VERY good LCD and Plasma ones have RGB input here in Brazil... even TV sets with S-Video are hard to find (the CRT ones), just like 29 inches flat screen have S-Video, and no RGB at all...
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Post Posted: Sat Jan 12, 2008 1:55 pm
Which is silly. It's decoding the composite/S-video to RGB to feed the three guns in the CRT anyway, it's just not letting you attach to that stage. But then there's nothing I can do about it...
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Post Posted: Sun Jan 13, 2008 2:05 pm
Someone actually hooked up RGB to a US TV without RGB input. Composite signal was used as sync, and RGB was fed to CRT guns directly (or something like it).

Anyway, why the hell is SCART / RGB rare outside Europe ? Even the cheapest TVs here have a SCART connector even though they have no RCA connectors, and that SCART connector usually has functional RGB pins...
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Post Posted: Sun Jan 13, 2008 4:48 pm
Historical reasons I would say.

Early TV sets used RF connectors to recieve a free-to-air transmission via antenna. There was no standardisation at the time for these connectors so specific to France they invented the SCART connector which later became mandatory on all TV sets.

Other countries had no such initiatives in place and so continued with the RF connector in its existing forms. Composite video sends all its colour information down one pipe eliminating the requirement for seperate R/G/B connectors and reducing cable clutter at most to 3 connectors (Video, Audio-Left/Right). This combined with the fact that composite video could be easily modulated with an RF frequency for use with existing recievers are probably factors towards its adoption.
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Post Posted: Fri Jan 25, 2008 11:35 pm
I've just noticed the diagram doesn't recommend the voltage rating for the capacitors, whats the minimum rating one should use?
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Post Posted: Sat Jan 26, 2008 12:30 am
djbass wrote
I've just noticed the diagram doesn't recommend the voltage rating for the capacitors, whats the minimum rating one should use?


Probably because the voltages in this part of the circuit are so low that the lowest voltage caps you're able to buy would be sufficient. I'd say a minimum of 4V.
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Post Posted: Sat Jan 26, 2008 4:51 pm
Mission acomplished!

Not having to tune the TV in anymore is a boon.

The only thing I have picked up is that I notice some graphics have some slight aliasing around their edges, whether this is normal and the RF usually hides this in blurring or not I am unsure.
smsav.jpg (200.67 KB)
SMS A/V
smsav.jpg

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Post Posted: Sun Jan 27, 2008 12:36 pm
G'day,
With the RGB mod if I wanted to use composite I assume the outer shield is earthed to pin 24 on the IC? If I wanted to use S-video would the 2 earths again got to pin 24?

Could you also split the audio to 2 outputs? I know it wouldn't be stereo but save having sound from only 1 speaker. BTW does the audio earth go to this pin 24 as well?
Cheers Pete
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Post Posted: Tue Jan 29, 2008 10:22 am
Found this site very helpful and as I suspected what I thought needed doing erm needed doing!

http://www.stickfreaks.com/smsmod.php
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Post Posted: Tue Jan 29, 2008 11:46 am
omp wrote
Found this site very helpful and as I suspected what I thought needed doing erm needed doing!

http://www.stickfreaks.com/smsmod.php
Note that this site only covers the S-Video and composite mods.
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Post Posted: Tue Jan 29, 2008 2:15 pm
Mike's mod takes audio from the Sega chip instead of the Sony chip like this guy did. What sort of difference would this make, if any?
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Post Posted: Tue Jan 29, 2008 2:33 pm
None at all, from looks the Sony chip just buffers the audio and little else. I don't see the point unless it has some effect on sync/timing?
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Post Posted: Tue Jan 29, 2008 2:46 pm
Mike's connection point seems to get the audio before it passes through a capacitor into the Sony chip. Maybe the sound quality is different there (capacitor = low-pass filter), or maybe it's a line level issue.

The "buffer" in the Sony chip will help protect the VDP/PSG chip from current demand and other nasty stuff caused by being attached to the outside world. I guess that's what the inline capacitor in Mike's design is for.
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Post Posted: Tue Jan 29, 2008 7:05 pm
Interesting, my audio output i got from even another point in the board...
I got mine from the solder points used in the RF modulator box...
Actually i couldn't see any differences between this point and the point in the VDP chip...
But my SMS III are Tec toy manufactured...
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Post Posted: Sat Feb 09, 2008 9:51 pm
Hi I only want to inform you that in many countries of europe the TVs, even if they have the scart connector, have NOT connected the R-G-B pins inside the TV anyway. So no point making the RGB mod for those TVs so complicated. The composite must be enough. Just try to look inside the TV (NOT RECOMMENDED FOR SHOCK HAZZARD) if there are more wires comming of the female scart connector. I have my TV only 3 years old, and I have there only 5 wires - audioL, audioR, composite and ground...
Just for consideration :)
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Post Posted: Sun Feb 10, 2008 12:58 pm
Every cheap TV I've owned supported SCART RGB and composite. S-video is the one that is usually missing.
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Post Posted: Sun Feb 10, 2008 1:31 pm
Maxim wrote
Every cheap TV I've owned supported SCART RGB and composite. S-video is the one that is usually missing.


my panscpmonic tv has svideo
yeah wwoohooo im durunk
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Post Posted: Sun Feb 10, 2008 10:45 pm
Thought I'd throw in some input here. My TV has s-video AND RGB through scart. Haha everyone :p
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Post Posted: Sun Aug 31, 2008 1:14 pm
TmEE wrote
viletim! wrote
...but you really shouldn't. They're there for a reason.


What reason ? If I put them into my MD I get slighlty worse picture...

Possibly because the TV you're using (or all) have them too... So it becames capacitor with capacitor in series -> "higher" hipass filter. No need for them, really.

I've built Mike's circuit but it appears "out of sync", ie, scrolling diagonally in one of my TVs, I've not tested on the other one. I'm going to take a picture and post it here.
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Post Posted: Mon Sep 01, 2008 1:15 pm
my TV has no caps in it... I usually use a 56...75ohm resistor in series to get the image dark enough... it seems to work, and there's not much room in my game consoles for capacitors, especially inside DC...
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Post Posted: Fri Sep 05, 2008 1:43 am
This is what I get, on the Sega's logo (SMS2's builtin Alex Kidd).
Anyone knows the cause?
IMAG0018.jpg (36.16 KB)
IMAG0018.jpg

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Post Posted: Thu Sep 11, 2008 7:52 pm
http://www.mikeg2.freeserve.co.uk/masterful/rgb.html

is dead, has anybody saved the site?
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Post Posted: Thu Sep 11, 2008 9:00 pm
http://www.smspower.org/masterful/
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Post Posted: Fri Sep 12, 2008 8:10 am
I'm glad that turned out to be useful.

It seems Orange (current owners of what used to be Wanadoo) have shut down all old hosted sites and required users to undertake a manual migration process to avoid losing everything. So a lot of stuff is lost forever - except for what's in the archive.
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Post Posted: Fri Sep 12, 2008 10:42 pm
"the archive" has it, dated Sep 11,2007

here´s the link:

http://web.archive.org/web/20070911120852/http://www.mikeg2.freeserve.co.uk/mast...
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Post Posted: Sun Sep 14, 2008 3:43 pm
Humm... no one knows the solution to my problem?
Because both the TV and SMS are PAL...
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Post Posted: Mon Sep 15, 2008 8:17 am
Since you have composite connected for sync, try just feeding it that. You'll want to change the switching voltage to 0V.
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Post Posted: Thu Sep 25, 2008 11:10 am
Thanks Maxim. Disconnecting 'Composite Sync' did not change the picture.

That happened because there was no composite sync given to the tv. Even if I followed the connections on the female scart@sms, the cable I was using (and all I think) switched the out<->in pins.

I followed Mike Gordon's 'SMS 2 RGB' where 'Comp Video' is connected to scart's pin 20 but in my case, I had to connect it to pin 19. (it's reversed in the cable and so gets connected to pin 20 at the tv).

I hope this helps others who 'fall' in the same problem.
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Post Posted: Thu Sep 25, 2008 11:43 am
Mike's guide is for a tethered SCART cable. The need to swap out<->in is an additional step if are installing a SCART socket to use with a standard cable.
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