Shuttle Invader PCB, Omori

Updated 18/9/22

I purchased this Omori Shuttle Invader PCB some time ago, just to see if it could be brought back to life. It's missing several parts but otherwise in reasonable condition so the initial challenge will be to 'fill in the blanks'.

Shuttle Invader PCB, Omori

And there are plenty of blanks, both onboard the PCB itself as well as in the Omori Shuttle Invader story generally. Not a lot of details have been unearthed about this obscure Japanese Invader 'clone' and I have discovered a few inaccuracies amongst the machine's existing 'knowledge base'

This PCB would have once belonged to a 'Shuttle Invader' machine, manufactured in Japan by Omori Electric Co. around 1979. As far as I know all such machines were of the Cocktail variety, using a monitor with vertical orientation and capable of flip screen, alternating two player operation.

Most descriptions I have read suggest the game exclusively used a Black and White screen with gel type coloured strips affixed but I've since concluded both Monochrome and Colour variants existed, the latter using a separate small PCB connected to the main by a ribbon cable to electronically apply a colour 'overlay' to the Black and White image. This is similar to the method used by Taito on their Space Invaders Colour machines.

The additional PCB was marked OEC-4A and contained a 256 x 4bit Bipolar PROM. Using the program 'YY-CHR' to view the contents of the PROM file graphically (left picture), there is a simple pattern which represents the colours enabled for each segment of the video image. Only 3 bits are used for each segment, representing the three CRT primary colours. The majority of the screen just has a single colour selected, presumably green while other areas are red or a combination resulting in yellow, magenta or cyan.

Shuttle Invader PCB, Omori Shuttle Invader PCB, Omori

Comparing that with the contents of a Taito Space Invaders colour PROM (right picture) the Taito PROM contains more data, the screen being divided up into more, smaller segments and there are two colour PROMs for the Taito as Player 1 and 2 each have their own colour overlay with slightly different colour selections but the principle is obviously the same for both machines.

As I only have the main PCB to work with I'll be attempting to repair the game as a purely Black and White unit unless I come across a matching colour overlay PCB at some point or decide to fabricate this small additional PCB from scratch, using original spec. componentry where possible.

4/8/22

I've had a bit of luck with the Shuttle Invader PCB project, sourcing a printed manual for the machine - which was apparently distributed by LAI in Australia at the time. This will make all the difference as the chances of repairing the PCB were not good with many missing and unidentified components and apparently no circuit diagrams available online.

How a number of obscure Japanese Invader 'clones' such as these made it to Australia in the first place is an interesting story, beginning with the introduction of Taito's Space Invaders in 1978. That machine rocked the arcade industry in Japan which had previously featured mostly electro mechanical or TTL based 'bronze age' video arcade titles.

The reaction to Space Invaders was enormous, demand to play the new title being so great in Japan that entire arcades soon sprang up, filled with dozens of Space Invader machines alone and an urban myth suggests the machines even caused a national shortage of 100Yen coins.

Not wanting to miss out on the 'Invader Boom' other manufacturers scrambled to build similar machines, from Logi Tec Co's almost identical 'TT' cocktail version to Nintendo's Space Fever and many others. Most of the Invader style machines were either Black and White, often with coloured 'gel' strips attached to the screen or colourised versions applying an electronically generated colour overlay to the originally monochrome graphics.

Within a year or so new machines were released with improved colour graphics and new challenges such as Namco's Galaxian and gradually the demand for Space Invaders waned. The 'Invader Boom' in Japan was over but the 'Golden Age of Arcade Video Games' had well and truly begun.

Imagine the surplus of Space Invader machines and clones when this occurred, arcades replacing them to satisfy demand for newer games. Meanwhile other countries in the Asia Pacific region such as Australia were still catching up with strong demand for Space Invaders and welcomed both new and pre-loved Japanese machines.

Some conversion was required, from Japan's 100V AC supply to 240V and 100Yen to 20c Aus. currency, adding instruction cards in English so it appears distributors such as LAI and even Taito Australia imported surplus machines and performed the necessary conversion for resale here.

In time, many of the more obscure models such as Shuttle Invader were considered less valuable than the 'genuine' machines and if they stopped working were most likely scrapped or the cabinets converted to other games so complete 'clone' machines in original trim are now rarer than ever.

The loose PCB which I have was probably removed from such a machine, stripped of useable parts such as CPU, EPROMs and even Crystals and narrowly escaped from being sent to land fill. Now it's time to try and return it to the land of the living.

The first task will be to replace missing components: 8080A CPU - already have. 18MHz Crystal - already have one, with a broken pin but can solder a wire onto. 5.545 MHz Crystal - have ordered the nearest available frequency I could find, 5.5296 MHz which is within 0.3% of the original and should work OK. It's a low profile, surface mount type but can be fitted to this PCB by soldering on leads if required.

Missing ICs; 8216 Bi directional bus driver IC x 4 - have a batch on order. 74LS30 and 74LS155, ordered. 14 and 16 pin IC sockets, 50k trimpot - already have.

And now for the EPROMs, Shuttle Invader uses 6 x 2708 1k x 8bit EPROMs, unfortunately I don't have any 2708s in stock or a suitable programmer for that type. I could probably order some old stock ones and adapt my existing programmer, adding the extra +12V and -5V supplies required by the 2708. Alternatively with slight alteration to the PCB tracks I could substitute 4 x 2716 EPROMs or 2 x 2732 EPROMs.

Another alternative and my preferred option at this stage would be to make up a small adaptor with a single 2764 EPROM which could contain the entire Shuttle Invader ROMset. Even better, a single 27128 16k x 8 bit EPROM could accommodate both the Shuttle Invader and the Sky Love ROMsets, with a small switch to select either 8k ROM 'bank'.

This adaptor would be installed without any modification to the existing PCB tracks so could be entirely removed if required to return to original configuration.

It's hard to imagine a game more obscure than Shuttle Invader but apparently Omori made a second game based on similar 8080 CPU hardware called 'Sky Love', before moving on to Z80 CPU based games. I'd like to try and get both of these games running on this PCB if possible.

18/9/22

I've made good progress with the Omori Shuttle Invader PCB repair project. The parts I ordered to replace missing items have all arrived so I can install them and set the PCB up to test on the bench.

Fitting the two crystals, the new 5.5296MHz item is a surface mount package, turns out this is the same as the through hole component except an insulating spacer had been added and the two pins flattened over during manufacturing to allow it to be surface soldered. Carefully straightening the legs allows it to be soldered into the existing PCB through holes. I've left the insulator in place to prevent the metal case shorting the PCB tracks underneath as there is no solder mask on this PCB.

Shuttle Invader PCB, Omori

The 8080A CPU and 8216 buffer ICs simply plug in to existing sockets and I'm fitting the two TTL ICs with new sockets. The PCB was a bit scorched under the 74LS155 so there may have been a short circuit in the previous component which had already been removed. I've cleaned the area as well as possible before soldering the new socket in place.

I had a change of heart about the EPROM configuration, while a single 27128 would accommodate the entire Shuttle Invader and Sky Love ROMsets and would be fine for testing purposes it would not be period correct for such an early PCB. Instead I've decided to install a full set of 2716 EPROMs with the Shuttle Invader program in the upper 1kByte of each IC and the Sky Love program in the lower half.

Shuttle Invader PCB, Omori

This will require a total of eight 2716 EPROMs, only six are initially required for Shuttle Invader but the Sky Love ROMset originally used eight 1k x 8 EPROMs so I've also programmed EPROMs 6 and 7 and installed new sockets in those positions. Substitutng 2716 EPROMs for the earlier 2708 components only requires slight modification to the PCB tracks and I've added a pullup resistor to the additional address line which will allow a switch to be added later to select the Sky Love program.

Having fitted all the parts the next step is to make up a bench test lead to suit the unique connections to this PCB. There is a Molex style header for the Power Supply Voltages, I already have some suitable connectors (which I purchased for the Chase H.Q. PCB repair) with some trimming as the header on the Shuttle Invader PCB only uses 11 positions instead of 12, 10 pins plus one key space.

Shuttle Invader PCB, Omori

There's also a 25 way PCB header for control inputs, Video and speaker outputs. It's similar in pitch to a common SIL PCB header but the pins are flat instead of square and I don't have a suitable mating connector. For testing purposes I've adapted a 28 pin dual wipe IC socket, cut in half and arranged into a single row using a small strip of Veroboard for wiring connections.

Shuttle Invader PCB, Omori

Adding some switches for testing of control inputs - the Shuttle Invader circuit requires both Normally Closed and Normally Open contacts to be connected for most inputs which use a flip flop style debouncing circuit. It adds a fair bit of wiring and means I can't just use my regular Quickshot joystick for testing inputs. Instead I've made up a little circuit board with ten small microswitches having Single Pole Double Throw (S.P.D.T) operation.

Shuttle Invader PCB, Omori

The switch functions are: Reset, P2 Fire, Left, Right, 2P Start and below: Coin, P1 Fire, Left, Right, 1P Start.

I've tested for shorts between any of the Voltage rails and ground with a multimeter and they all seem OK so, with all of the connections made it's time to power it up and see what we get...

Shuttle Invader PCB, Omori

Amazing! The game is running, even has sound. The Video levels look wrong but it could be soooo much worse, all I've done so far is replace missing components. I'd better have a look at those Video levels.

It's no surprise that my NEC TV monitor is having trouble with the Video signal, there's about 5 Volts of it and most of that is sync. A standard composite Video signal is 1Volt, 0.7V Video above 0.3V Sync. Looking at the Video output stage on the Shuttle Invader PCB there are some component changes from the circuit diagram with some load resistors omitted and output resistor replaced by a link.

Shuttle Invader PCB, Omori

It could be that this game PCB was used with the optional colour overlay PCB in which case the Monochrome Video output would have been used as the source of sync for a colour arcade monitor (that would explain the unusually high sync level and muted video on that output) or it could have been set up for a non-standard signal level to suit a particular Black and White TV monitor.

Early Black and White games such as this often used an AV modded TV set for a monitor and depending how the Video was inserted into the signal path a specific level may have been required. More modern TV monitors on the other hand are designed around a standard 1Volt composite Video input signal.

Anyway, changing R10 to 120 Ohm, installing 330 Ohm R40, changing output resistor R42 from zero to 68 Ohm and adding 560 Ohm load R41 returns it to original configuration. R41 was actually listed as 510 Ohm but 560 is close enough as it is just a load for the common Collector output transistor TR1 and won't affect the gain - Common Collector (a.k.a. Emitter follower) stages are usually used as buffers and have a unity gain.

Shuttle Invader PCB, Omori

That's improved the situation a lot but we're still getting about 3 Volts of Video. That white band at top of screen isn't Video noise or hum but a clamping problem, after Vertical sync the black level is set way too high but eventually recovers. Hopefully padding the signal down to correct levels may help with that.

So, increasing the output resistance from 68 Ohm to 270 Ohm by trial and error reduces the signal to a 'standard' 1Volt level. The image is much improved and is fine for this test setup but might need trimming if an original Black and White TV monitor is used at some point.

Shuttle Invader PCB, Omori

Moving on to test the game play, all appears to be working except for a missing 'UFO flying' sound. All the other sounds are present though slightly different to the more familiar Taito (or Midway) versions of Space Invaders sounds including the Invader marching sound which in this case seems to be a single note rather than the famous 4 note progression.

Interestingly, even though the game had a full set of sounds on board there was an additional sound PCB added to some machines. I'm guessing the idea was to replace the slightly 'different' original sounds with something closer to Space Invaders in the hope that if the game sounded more like a 'genuine' machine more people would be attracted to play it.

That's just speculation really though the additional sound board is documented and had the board number OEC-5. It connected directly to the speaker, replacing all on-board sounds and was controlled via a ribbon cable from the main PCB connector CN4. It appears this particular PCB was never paired with the additional sound PCB as the DIP socket at CN4 was not populated.

So, all that remains is to troubleshoot the missing UFO flying sound and then try to also get the Sky Love game running on this PCB, if possible.

To be continued...

Web Resources (External Links) -

Shuttle Invader Part II Flyer - flyerfever.com

Sky Love Flyer - flyerfever.com - Colour version

Sky Love Flyer 2 - flyerfever.com - Note alternate colours shown on screenshot.

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