Master System:Video Output Notes
Mark III
The Sega Mark III is the original version of the Master System hardware and was the first Sega console to have a video output better than RF, featuring both composite and RGB output sent through an 8-pin DIN connector (specifically the 262 degree or "U-shape" variant). While the composite output is suitable for practically any display without external components, the RGB output is not, as it comes directly from the VDP and hence requires amplification. A cable with a built-in amplifier such as the French SCART cable (detailed in the section below) can be used, or the console itself can be modified with an internal amplifier, making it compatible with standard Master System and model 1 Genesis/Mega Drive RGB cables.
To generate composite video, the Mark III's video encoder, a ROHM BA7230LS, converts the RGB into component video, which is then fed back into the encoder to create a composite video signal. The resulting signal is bright but is rather blurred and not quite as saturated as later Master Systems. Given that the BA7230LS generates component video, it may be possible to modify a Mark III for this output, but no such attempt has been made as of yet.
The Mark III's composite output can be slightly improved by connecting pin 20 of the BA7230LS to ground using a 1 uF capacitor. Pin 20 is an unused composite video input, which according to the datasheet must not be left floating (disconnected); there are footprints for the necessary components on the Mark III's motherboard, but for some unknown reason these were left unpopulated. This can be remedied by populating C96 with a 1 uF capacitor and R97 with a jumper link.
French Master System II
The French Master System II offers RGB output and was shipped with a special SCART cable. Unlike other French consoles that offered RGB converted from composite, RGB on the French SMS II is native RGB output directly from the VDP. However, because the RGB output comes straight from the VDP (much like the Mark III), it is not amplified and requires the SCART cable that came bundled with the console. This is because the SCART cable contains an amplifier circuit which makes this RGB output suitable for most displays.
The French SMS II also does not output composite video as it does not contain a video encoder chip, and the DIN pin which normally carries this signal is unused.
Japanese Version (MK-2000)
The Japanese Master System (often referred to as the MK-2000) does not require any components on the CSYNC line. When connected to a display or processor, it will output around 350 mV without anything else needed. In fact, all four lines (red, green, blue and sync) all have the necessary components on the motherboard, so the RGB cable will just be a full pass-through cable. This is the opposite of all other SMS revisions, and using RGB cables meant for these consoles on the MK-2000 will result in a dimmer picture. The HD Retrovision cable can compensate for this with its contrast switch, but this can pose a problem otherwise.
Alternatively, four sets of 75 ohm resistors and 100 uF capacitors in the console can be removed and replaced with jumper links, allowing for the use of regular SMS RGB cables. Capacitors C41 through C43 and C45, and resistors R41 through R43 and R45 must be removed, then jumper links can be added so the output pins on the CXA1145 go directly to the DIN connector. The jumpers must be connected as shown in the photo below; do not remove C44 and R44 as those are for composite video. Note that the solder pads for these components are very fragile, so great care must be taken when desoldering these components.
The extra resistors and capacitors for RGBS on this Japanese SMS have been removed and replaced with jumpers so standard cables can be used.
This is the stock RGB output from a Japanese SMS using a standard Genesis/SMS SCART cable.
With the internal components removed, the RGB output is considerably brighter.
RGB Cable Components
For all other SMS consoles with RGB output, all RGB cables that use CSYNC should have a 470 ohm resistor and a 10 uF–220 uF 10 V minimum capacitor with the positive leg facing the console on the sync line (pin 7). A 10 uF capacitor is all that's needed, but it is also very common for people to use 220 uF. Either way, the voltage rating shouldn't be below 10 V. Composite video can also be used for sync. The red, green and blue signals must have 75 ohm in-line resistors as the picture will be too bright and washed out without them.