Taito Space Invaders arcade machine

I have always wanted my own sit down arcade machine at home

A few years ago I made a purchase that would have been a dream come true when I was back in school. When I was at school, arcade games ruled and home computers and consoles had fairly poor conversions of those games. My new purchase was an original Taito sit down Space Invaders arcade machine. It was like being ten years old again.

If I had owned this machine back when I was in school, then I would have probably been the most popular pupil there. But alas, back in those days, these machines probably cost and arm and a leg to buy. And maybe not even available to the general public?

Buying one and getting it home

I just happened to come across it on eBay when doing some random late night searching, as you do. Luckily the locations was only about 10 miles away so I put in some bids and I won it for about £250 and it was mine. Picking it up was fairly easy. My car at the time was not big enough to put this into, but my father had a people carrier that you could remove the rear seats from. The arcade machine fitted in the back no problem. When picking it up, we established that it was possible to unbolt the legs from the main cabinet. This made it easier putting it in the car and also less wobbly when cornering. We got it home with no damage. Well, apart from my fathers back which was aching the next day.

There are two types of sit down Taito Space Invaders machine. One with a black and white screen and one with a colour screen. Mine is the latter type. I would prefer the black and white version as this would be an earlier one than mine. If I can find the parts on eBay, then I might convert mine later on.

The machine is a two player game and each player sits either side of it. When it is the turn of the second player, the image on the screen flips around for them. And then flips back for player one, when they lose a life.

Initial work as it has the wrong game installed

When I say it is a Taito Space Invaders machine, it is as far as the cabinet goes, but it no longer had the Space Invaders PCB set inside it. It had had a conversion to a pool game called Video Pool. This game is actually quite good for its time and can take some skill to play it well. But Space Invaders was my goal. Luckily there was no physical modifications as the pool game used the same controls. And it looked like the internals of the machine were also unmodified. The auction clearly showed there was a conversion to a pool game in the past, and I was aware of this before bidding on it.

The search was on for a Taito Space Invaders PCB set. This was a costly exercise as they are getting collectable and when I found one, it cost me about half the price I paid for the arcade machine. Later on I found two more PCB sets and got them as well for spares. It is amazing how big the PCB set is just to play one game.

Arcade machines used an interface called JAMMA ( Japan Amusement Machine and Marketing Association ) that standardised the arcade machine connectors to the game PCB’s. This allowed cabinets to have their games changed easily with little effort for the arcade operator. But the JAMMA standard did not come in until 1985. This Taito machine uses its own PCB connector and the Video Pool PCB set also used the same connector. So there must have been some sort of standard in place before the JAMMA standard become the norm.

I was able to simply unplug the Video Pool PCB set and plug in the Space Invaders PCB set. Before doing this I had checked circuit diagrams which are freely available to download to make sure it was all compatible. After lots of checking and crossing my fingers, I powered up the machine.

Drat, it did not work. The screen was blank. I have a career background in electronics, so I went into fault finding mode. Out came the oscilloscope and I checked some things over on the new PCB’s. It turned out the CPU was not getting the correct reset signal when the machine powers up. The reset signal comes from the power supply. This has been wired slightly different on the Video Pool PCB set and I was able to see how someone had to change a wire to make that work. So I just moved the wire back to its original pin on the connector. And lo and behold, when I powered up the machine, I can see my beloved Space Invaders.

And to recoup a tiny bit of money, I put the pool PCB set on eBay and got £20 for it.

Fixing the faults

So hopefully this is it and it will be working fine now. I was able to add a credit and indeed play a game. All the buttons and controls seemed to work fine. But there was still one issue left. No sound.

The Space Invaders PCB set consists of three PCB’s. They are on top of each other and are connected with ribbon cables. The first PCB has the CPU and RAM on it. The second PCB has the ROM’s on it. And the third PCB has the sound effect circuits on it. This was all cutting edge for its time. The CPU is an Intel 8080 clocked at 2MHz. The whole game runs using 8K of RAM and 8K of ROM. Sound comes from a Texas Instruments SN76477. The game uses seven sound effects ( missile shot, invader hit, saucer hit, explosion, saucer sound, bonus missile base and enemy heartbeat ) and each one has its own amplifier circuit and volume control, and there is also an overall volume control. This is clever as you can fine tune the volume of each sound effect in the game and make it louder or quieter.

On the sound board there are a number of operational amplifiers ( op-amp ) on individual chips. There is one for each of the seven sound effects and some others for the overall sound output. I checked around the overall sound output area with my oscilloscope and it was apparent that a main op-amp chip had died that drives the speaker. I replaced this and then the sound was working, but not completely. Some of the sound effects were silent. This was down to the op-amp chips for those sounds also going bad. Replacing those finally got all the sounds working properly. After adjusting the individual sound effect volume controls and the overall volume control, I got it setup nicely and it was working really well.

My Space Invaders playing technique

Listen carefully, I shall say this only once. This is my top tip for playing Space Invaders. There are many methods for clearing the attack waves, but this is how I do it. The enemy invaders get lower and lower when the formation reach the sides of the screen. So my technique is to slow this process down. So I work on the sides of the formation and this reduces the number of enemy ships, and this makes it take longer for them to reach the sides. The enemy ships will speed up as the numbers reduce, but it is all manageable.

I often find the shields to be more of a hindrance than for protection, but they do come in handy sometimes. I have no problem shooting right through them if needed to get my kills.

There is a flying saucer ship at the top which occasionally flies across the screen. I do not really go out of my way to hit this, but I will certainly give it a go if I am able to. There are techniques where you can count your shots before hitting this flying saucer ship and you will get 300 maximum points for it. I do not really bother with this and just hit it when I can. I do not really play for high scores and prefer just to clear attack waves.

Each new attack wave has the enemy formation starting lower and lower. At a certain level the shields will not be visible as the enemy formation is too low. When you reach a level where the enemy formation is right at the bottom of the screen, there is a little trick you can do. You can move your base across the screen and shoot off the lower row, and they cannot hit you with return fire. You can keep doing this as they move down, but you must hit every enemy ship in the lower row perfectly.

Did my friends like it?

I have had friends over since getting this and they absolutely loved it. They could not believe I had an actual arcade machine in my house, and such a historical one as well. Space Invaders was always popular with anyone who went to the arcades back in the day. It is a bit like never forgetting how to ride a bicycle and they were playing it just as they remembered. Each using their own tactics on how to complete each wave of invaders.

The coin slot takes old 10p coins and I do not have any. I think adjustment for other coin sizes is possible, but I have not looked into this. Luckily inside under the top cover is a credit button and you can add more credits easily. Caution is paramount as there are live mains connections and you could easily get an electric shock if you are not careful. I think for a party where people would be drinking, this method of adding credits might not be so good. So fitting some sort of external credit button would be a good idea, or get some old 10p coins and use the slot as intended.

Future work

The machine is in pretty good condition, but it could be better. Here are some jobs I will do when I get enough time.

• The joysticks are very loose to use. I have not looked into this yet, but I am hoping it is just a case of something coming undone and not parts wearing out.
• The print on the control panels has worn from lots of use. I have now purchased some new reproduction control panels which look great.
• The wood on the cabinet just needs a little work here and there to make it look nicer.
• The metal legs have have broken welds and the machine wobbles when you play it. The legs have broken from people sitting on the table top in the past. They cannot take this sort of weight. Some simple MIG welding will fix this. And being chromed again would be nice.
• The glass top is a little scratched. I am not sure if there is much I can do about this. Replacement glass would probably be very expensive as it looks very tough. I might have a go with a car windscreen scratch removal kit, or just live with it.
• The Space Invaders PCB set is loose as it has not been secured. I need to work out how this was originally done and secure it properly.
• The hinged top has no stay to keep it open when you are working on it. I doubt I will be able to get the correct stay, so I will have to make something myself.
• The metal around the coin drawer is all bent as someone has tried to lever it open to steal the money. This must have happened a long time ago when it was being using in an arcade or a pub.
• From years of use there is dust all over the inside and it could do with a really good clean.
• Instruction cards. These are under the glass and are still for the pool game. I have found some Space Invaders ones online and I need to print them off and fit them.