Space Invaders 2 Cocktail on Taito

[Andywarne]

Just for fun I thought I would try to get this little-known SI head-to-head version running on Taito hardware.

This used 2 sound boards but it should be possible to modify a standard Taito sound board to act as the second board. I think most of the connections to this second board could be made by using a special 3-way ribbon cable as one of the inter-board cables. I have several boards with the MB14241 missing so one of these would be ideal.

The first hurdle was to get the game to run at all. For some reason there is an addressing hole in the ROM structure, so this meant adding some sockets to the Taito board and setting the jumpers for these sockets correctly. Also Midway ROMs are numbered (or lettered) in reverse order to the addressing. Having got it to run I will start investigating the second sound board.

Andywarne2018-06-04 10:11:11

 

[Hurray Banana]

Nice bit of hackery there

Never seen that space invaders variant, interesting

 

[big10p]

Yeah, that's new to me, too. Nice.

 

[Andywarne]

Another little challenge is this originally ran as a monochrome game with colour filters. So running on a colour board/monitor means the colour mapping is wrong.

I am not sure what the overlay actually looked like, but I will need to create a new colour Prom to correctly map the colour areas.

 

[Andywarne]

2 sound boards working! At the moment they are both producing the same sounds.

The normal sounds are controlled by I/O ports 3 and 5. On the original second sound board the player 2 sounds are controlled by ports 1 and 7. So I will need to do some cutting/wiring to change this on the board. Then I need to work out all the component differences which make the player 2 sounds different to player 1.

On the inter-board cables I have cut any unwanted signals which originate in the second board so that only inputs are routed to this board, basically this means disconnecting the multiplexed controls bus and a few other signals.

Andywarne2018-06-05 21:20:22

 

[Andywarne]

Managed to get all the board sound mods done. There are only 5 component differences.

The player 2 sounds are not much different in fact from the standard sounds. the UFO sound is slightly different and invader hit sound has a kind of double "echo" to it. There is a component change in the laser fire sound but I cant hear any difference.

So the reason they used two sound boards in this game seems not to be to provide different sounds, but to provide the sound for each player to be independent. So that if the 2 players hit an invader for example at almost the same time, both sounds would be generated in full. With one board the second sound trigger would not work properly, with the way these sounds are produced.

 

[Hurray Banana]

Interesting Andy and makes sense to have two separate circuits, no 256 voices back then

 

[Andywarne]

All done and working!

Taito 4-board set

Just need to finish refurbing a table to put them in.