Sega Master System FM Sound Expansion Board

The Japanese Sega Master System included a Yamaha YM2413 FM synthesis chip along with the standard PSG sound. Many games, some of which were never even released in Japan, contain extra FM sound and music. Installing this board will add FM sound capability to any Master System or Mark III game console. The first post in this thread contains a list of games with FM sound. A switch is provided with the board to disable the FM chip and revert to the PSG sound whenever desired.

New in version 2.0
One of the most popular games with extra FM sound is Monster World III: The Dragon's Trap. This game is programmed to use the FM sound hardware only if it detects that is is running on a Japanese SMS (or Mark III). Hardware version 2.0 and above has a region switch feature. Instead of a two position switch, a three position switch is now supplied which can be used to select between off position (PSG), FM, or Japanese/FM.

New in version 2.2
The method for region switching (disable the I/O chip with KILLG# upon receiving a write to port 0x3F) is not totally reliable. Approximately 5-10% of consoles do not respond. Hardware version 2.2 fixes this problem with the addition of one extra wire to the installation. In late 2014 there was some extra details discovered about the Japanese SMS sound hardware on detailed in this thread. The benefit is there are no longer 'extra' sound effects playing in Outrun at the start of a race.

Version 2.2 is compatible with all known games with functioning FM sound support. Some of these games were released only in Japan.

After Burner Golvellius - Valley of Doom Scramble Spirits
Alex Kidd: The Lost Stars Great Golf * Shanghai
Alien Syndrome Hoshi wo Sagashite... Shinobi
Altered Beast Kenseiden Solomon no Kagi - Oujo Rihita no Namida
Aztec Adventure Lord of the Sword Space Harrier 3-D
Blade Eagle 3-D Maze Hunter 3-D SpellCaster
BMX Trial Alex Kidd Megumi Rescue Super Racing
Bomber Raid Miracle Warriors Tennis Ace
California Games Mônica no Castelo do Dragão Tensai Bakabon
Captain Silver Nekkyuu Koushien Thunder Blade
Casino Games Out Run Time Soldiers
Cloud Master Out Run 3-D Turma da Mônica em: O Resgate ++
Cyborg Hunter Parlour Games Ultima IV: Quest of the Avatar
Double Dragon Penguin Land Vigilante
Fantasy Zone II Phantasy Star ** Wonder Boy III: The Dragon's Trap ++
Fantasy Zone: The Maze Poseidon Wars 3-D Wonder Boy in Monster Land
Galactic Protector Power Strike Y's: The Vanished Omens **
Galaxy Force Rampage Zaxxon 3-D *
Game Box Série Esportes Radicais Rastan Zillion II: The Tri Formation
Global Defense Rescue Mission
Golfamania R-Type

* Only the North American and Japanese release supports FM sound.
** Only the Japanese version supports FM sound. It was removed from other language versions.
++ This game requires the region switch set to Japan to play FM sound.

For those that have Pro Action Replay / Flash cartridges: The following games support FM sound but require a with a minor patch to make it work. More information here.

Battle Out Run
Double Hawk
Dynamite Dux
Rambo III
Summer Games

For those with Flash cartridges: There are some interesting patches available.
Ys US Master System FM sound patch A patch for the Ys US version to put FM sound back in.
Phantasy Star retranslation Phantasy Star Japaese to English translation, has FM sound intact.
Sonic 1 FM Sonic with new FM music.

Version 2.2 - Available now.
Circuit Diagram
Logic Equations (AHDL)


The SMSFM board is designed to plug into the expansion slot of an original model Sega Master System console. To fit the board, first remove the screws and open the console. Plug the SMSFM board into the expansion connector. It fits in the cavity behind the cartridge slot and does not require the plasic cover of the expansion port to be punched out. It is usually necessary to cut away part of the metal shielding for the SMSFM board to fit.

A switch is provided to disable the SMSFM board. This is useful for games which you prefer the PSG audio and a few games that crash when they detect FM sound hardware. The version 2.2 board comes with a three position switch. The third position switches the region of the console to Japan. The region switching feature doesn't work on all consoles. If it doesn't work please see instructions for adding the extra region switch wire towards the bottom of the page.

Audio Mixing
Installation requires some soldering for audio mixing. A capacitor in the audio circuit is removed and a two core shielded cable soldered into its place. The standard (SN76489/PSG) audio signal is sent into the SMSFM board via the white wire, is mixed with the FM sound signal, and sent back through the red wire. The cable shield should be connected to ground to reduce noise. Trimpot RV1 controls the volume of the FM sound only. What follows is a collection of instructions for connecting the audio mixing wires to various different version of SMS main board. Please let me know if you can't find one that matches your hardware.

PAL SMS (original 1986)
Capacitor C48 (10µ aluminium electrolytic type) is removed, the white wire is soldered to the +ve hole and the red wire to the -ve hole. There's a large ground plane nearby to attach the shield. Access to this cap first requires the removal of the voltage regulator heatsink. This is done by first removing the screw on the 7805 voltage regulator with a long shaft screwdriver, then unscrewing the two screws holding the heatsink to the PCB. Don't forget to reattach the heatsink before you finish!
Location of C48

Capacitor C31, located beneath the video encoder IC, is removed. White wire to -ve, red wire to +ve, and shield to nearby ground point at the -ve leg of C44.
Location of C31, SMS2

Remove C37, white wire to +ve, red wire to -ve. There's a ground plane around the base of the capacitor so just scrape off a bit of the green stuff and solder the shield to that. The heatsink on the voltage regulator many need to be removed for access (remember to put it back!). Because this PCB does not have plated through holes, soldering cannot be done from the component side.
Note that the diagram below is incorrect, the white/red indicators are swapped around.
ntsc.jpg (54596 bytes)

Late model PAL SMS (VA3)
Remove C62, white wire to -ve, red wire to +ve. The shield is connected to a nearby ground plane - the leg of C59 looks like a good choice.
va3.jpg (76028 bytes)

Brazilian Tectoy SMS (original version)
Locate CI-5, the 315-5124 VDP. Find the trace running from pin 10 and cut it close to the IC. Solder the white wire to pin 10 and the red wire to the positive leg of C45 (that's where the trace goes). I also have a circuit diagram for reference.
brazil0.jpg (54370 bytes)brazil1.jpg (35770 bytes)

Original NTSC SMS (1986)
Remove capacitor C49, located left of the centre in the photo below. Solder the white wire to the +ve leg hole and the red wire to the -ve. Solder the shield to the nearby ground plane or the RF modulator's metal casing.
ntsc1986.jpg (31466 bytes)

French M4 SMS (no video encoder, requires the Adapteur RVB)
Remove the yellow wire between the place for C37 and the place for IC9. Solder the white wire to the +ve leg hole of C37 and the red wire to IC9 pin 9. Solder the shield to the nearby ground plane (scratch off the green) or to pin 1 in the place for IC9. Because this PCB does not have plated through holes, soldering cannot be done from the component side.
french.jpg (97065 bytes)

Generic SMS (those not listed above)
Trace the audio signal from both the RF modulator and A/V port (if there is one) until they meet at a common point. Trace the audio signal back further (it may go through an opamp or audio buffer inside the video encoder IC) until you find an electrolytic capacitor in the signal path. White wire = input to SMSFM board, red wire = output. Find a ground connection close by and attach the shield. Keep in mind that the input and output are electrically the same as those on a stereo system. There's no reason why standard phono sockets can't be attached and the mixing done with external leads.

Solder Version
This is simply a board without a 50 pin edge connector fitted. In order to install the board into a SMS2 or Mark III you will need to do a bit of soldering.

In addition to the audio mixing, the solder in version requires 18 wires to be connected between the SMSFM and the Sega motherboard. The type of wire using is not critical. Use what you are comfortable working with, thin wire is usually easier.

Solder diagram for PAL SMS 2  (updated)

KBSEL# is unused and should be left unconnected.

SMSFM2_solder_pins.png (6701 bytes)

Extra wire for region switching.

Some consoles require an extra wire for region switching to work correctly.
The wire carries a modified IORQ# signal for the I/O chip. The IORQ# pin should be isolated from the rest of the circuit, either by cutting the track on the PCB or cutting and lifting the pin itself. Solder a wire between IORQ# pin and the IORQ# pad clearly marked on the back of the SMSFM.

Sega 315-5216 - I/O chip inside an original Master System. IORQ# is pin 23.

Sega 315-5237 - I/O chip inside a Master System 2. IORQ is pin 1.


See the etim online shop for price and availability.

Historical Hardware

Version 1.0 - 2007
Circuit Diagram

There was a small problem with this board which made it incompatible with a few of games. Read this discussion on the SMS Power forums for more information and a fix. Many boards also contained a defective YM2413 sound chip, read more about it here.
cs_con.jpg (10968 bytes)ss_con.jpg (15580 bytes)

Version 1.1 - 2009
Circuit Diagram

top.jpg (27598 bytes)bottom.jpg (36106 bytes)
Version 2.0 - 2012
Circuit Diagram
Logic Equations (AHDL)

SMSFM2_small.jpg (50420 bytes)

Version 2.1 - 2014
This version is almost identical to 2.0. The included three position toggle switch is smaller. When solder jumper JP4 is bridged, two independent switch may be used to switch region and FM enable.
SMSFM21.jpg (38667 bytes)

Changelog (D/M/Y)
18/2/15 - Removed some info about old versions of the board. Rearranged the page a bit. Added details for the V2.2 board, the game compatibility list, and instructions for the extra wire for region switching.
2/4/14 - Added information about reliability of region switching, link to shop.
15/2/14 - Revised time when new stock is expected.
17/11/13 - Run out of stock.
20/7/13 - Added diagram for French M4 board revision.
13/5/13 - Shop is open again.
26/4/13 - Shop is temporarily closed.
26/1/13 - Added information about V2.0 + shop + diagrams for the audio mixing in the Brazilian Tectoy SMS.
12/8/10 - Added note to NTSC SMS instalation instructions, I'll make a correct diagram one day when I have time.
29/8/09 - Updated with details on the new v1.1 board.
10/1/08 - Page created


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