Refurb weekend: Gremlin Blasto arcade board

Because my sisters were taking rollerskating lessons and my own rink skills mostly consisted of pratfalling, my mother would occasionally give me quarters for the arcade instead. This was my first introduction to pinball — one of these days I'll have room for my first pin, a Williams Pin-Bot, alongside my Sopranos and ST:TNG machines — and quite a few arcade video games that I later got to play on my Tomy Tutor, Commodore 64 and Intellivision at home.

However, a few games I played on the Tutor first before I ever played them on an arcade cabinet (Pooyan and Loco-Motion come to mind), and one outlier I never played in the arcade at all. Earlier, when we briefly lived in the Antelope Valley north of Los Angeles, the first computer I got to ever touch (albeit briefly) was a Texas Instruments 99/4A in the third grade classroom. Among other cartridges it had a brisk and zippy arcade conversion called Blasto from Milton Bradley which never got ported to any other system, and it wasn't until after college that I reacquainted myself with the TI version in emulation. I never actually got to put quarters in one.

A shame, because by then we lived on the mean streets of east county San Diego, California — not far, it turns out, from the corporate office of Gremlin Industries where the original arcade incarnation of Blasto was developed (completely unrelated to the later PlayStation game). I spent most of my childhood and got my bachelor's degree in San Diego, and I still consider it my hometown. Decades later I managed to pick up an original service manual for yuks last year, which sat mostly pristine in my collection, but much more recently an actual Blasto logic board based on an 8080A CPU turned up on eBay.

After waiting awhile for the seller to cut the crap, they finally posted it at a not totally unreasonable price for a completely untested item, as-was, no returns, with no power supply, no wiring harness and no auxiliary daughterboards. At the end of this article, we'll have it fully playable and wired up to a standard ATX power supply, a composite monitor and off-the-shelf Atari joysticks, and because this board was used for other related games from that era, the process should work with only minor changes on other contemporary Gremlin arcade classics like Blockade, Hustle and Comotion [sic]. It's time for a Refurb Weekend.

Gremlin Industries effectively got its name from a careless bureaucrat. Electrical engineer Frank Fogleman, fed up because his first San Diego company collapsed after its contract manufacturers began selling his own product against him, decided to walk away and start over fully controlling the production process. He partnered with fellow engineer Carl Grindle to form what was supposed to be called Grindleman Industries, but the name was reportedly misheard over a long distance call to the Delaware registrar, and Gremlin Industries stuck. Some of the photos and history in this segment come from a July 1982 San Diego Reader article, the locally famous alternative paper I always snitched a copy of when I was downtown, and of which I found a marginally better copy to make these scans. There's also an exceptional multipart history of Gremlin you can read but for now we'll just hit the highlights as they pertain to today's project.

The new enterprise set up shop in 1970 at a rented industrial suite on 7030 Convoy Ct in Kearny Mesa. Initially Fogleman, officially president, produced more utilitarian industrial and nautical equipment similar to what he built previously, even winning a contract to build French fry cooker timers for nearby San Diego company Jack in the Box. (My wife still tolerates my periodic jonesing for a Supreme Croissant.)

In 1972, however, the company's focus rapidly changed after a customer asked if they could help with repairs for their wall games. In those days, a "wall game" was an early sort of electronic coin-op common in 1970s bars, using simple discrete circuitry and light bulbs behind a large static translucent playfield, mounted to the wall and playing crude button-controlled versions of games like darts, golf or skeet shooting. Company VP Jerry Hansen found the games simplistic and shoddily constructed, and told the customer he could do better, only for the customer to say that the units already made plenty of money. Hansen convinced the rest of management to see if they could make a wall game of their own, and the result was 1973's Play Ball: it had audio, high quality art, a better skill challenge, and even Gremlin's willingness to extend income guarantees to sceptical distributors.

Play Ball was so successful, in fact, that Gremlin dropped their other business lines to concentrate entirely on wall games. Within a year Gremlin became undisputed king of the market segment, moving from the Convoy location to a new 56,000-square foot plant at 8401 Aero Drive. (This location later became part of the San Diego Community College District, and is now a private bilingual French school.) Wall games, however, were on their way out and Gremlin management knew it. Although Gremlin's units were well-regarded, they were hitting the complexity and gameplay limits of what even TTL logic could do, and the company had no experience with the new frontier of microprocessors.

Fortunately, their new hire in 1975 did. Lane Hauck, working at Lockheed in the early 1970s, failed to convince management that computers were the future and they should buy one, so he bought one himself: a $5500 [about $40,000 in 2025 dollars, give or take] DEC PDP-8. When he quit Lockheed and took a new job with electronics manufacturer Spectral Dynamics in their San Diego office, the PDP-8 went with him, stuffed into his back bedroom in Clairemont. In addition to learning to program it himself in assembly language, he became fascinated by a particular PDP-8 game called MOO. MOO is a very old logic deduction game, known to prior generations as Bulls and Cows where you guess a four digit number (a digit correct and in the right place is a "bull" and correct but in the wrong place is a "cow"), and was a forerunner to the more modern game of Mastermind. MOO was also ported to V1 Unix and has a simpler three-digit variant Bagels which was even ported to the KIM-1. Unfortunately his friends didn't have minicomputers of their own, so Hauck painstakingly put together a complete re-creation from discrete logic so they could play too, later licensed to Milton Bradley as their COMP IV handheld.

Hauck had also been experimenting with processor-controlled video games, developing a simple homebrew unit based around the then-new Intel 8080 CPU that could connect to his television set and play blackjack. Fogleman met Hauck by chance at a component vendor's office and hired him on to enhance the wall game line, but Hauck persisted in his experiments, and additionally presented Fogleman with a new and different machine: a two-player game played with buttons on a video TV display, where each player left a boxy solid trail in an attempt to crowd out the other. To run the fast action on its relatively slow ~2MHz CPU and small amount of RAM, a character generator circuit made from logic chips painted a 256x224 display from 32 8x8 tiles in ROM specified by a 32x28 screen matrix, allowing for more sophisticated shapes and relieving the processor of having to draw the screen itself. (Does this sound like an early 8-bit computer? Hold that thought.)

Fogleman was hooked and immediately authorized a test of what he quickly christened "Blockade." Built using a simple cabinet and a consumer TV set, the prototype was deployed to an arcade at what I think was still the Family Fun Center back then (it later became a Boomers!, and is now closed), at Clairemont Mesa Blvd and Interstate 805, and made enough money in its first night to convince Fogleman it should go into production as soon as possible. Hauck added a tone generator and a "boom" circuit triggered by crashes, as well as wiring in extra lines for a four-player variation called Comotion [sic] ready for public demonstration at the same time.

Unfortunately for Gremlin, the video game market was heating up, and less scrupulous competitors lurked around every corner. At the November 1976 Amusement and Music Operators of America show in Chicago, Gremlin's Blockade and Comotion prototypes overshadowed everything else at the convention and rapidly racked up thousands of pre-orders, but Gremlin didn't have the manufacturing capacity of their competitors — who had already taken notice of the new game. Within months, Atari brought out Dominos [sic], Midway introduced Checkmate and Ramtek presented Barricade, all companies with greater experience in electronics manufacture and all painfully obvious clones of Blockade, leaving Gremlin as the last to arrive in the segment they themselves created. Gremlin had never copyrighted their game code, and their hastily filed patent application was too late and too slow to stop the ripoffs. (For the record, Atari programmer Dennis Koble was adamant he didn't steal the idea from Gremlin, saying he had seen similar "snake" games on CompuServe and ARPANET, but Nolan Bushnell nevertheless later offered Gremlin $100,000 in "consolation" which the company refused.)

Meanwhile, Blockade orders evaporated and Gremlin's attempts to ramp up production couldn't save it, leaving the company with thousands of unused circuit boards, game cabinets and video monitors. While lawsuits against the copycats slowly lumbered forward, Hauck decided to reprogram the existing Blockade hardware to play new games, starting with converting the Comotion board into Hustle in 1977 where players could also nab targets for additional points. The company ensured they had a thousand units ready to ship before even announcing it and sales were enough to recoup at least some of the lost investment. Hauck subsequently created a reworked version of the board with the same CPU for the more advanced game Depthcharge, initially testing poorly with players until the controls were simplified. This game was licensed to Taito as Sub Hunter and the board reworked again for the target shooter Safari, also in 1977, and also licensed by Taito.

For 1978, Gremlin made one last release using the Hustle-Comotion board. This game was Blasto.

Blasto used Hauck's hardware but was written by programmer Bill Blewitt. By this time Gremlin was writing their game code on an internal 8080A development system to speed time to market (I said hold that thought) and the games could be somewhat more complex within the capacity of available ROM. In some respects Blasto's one- and two-player modes were qualitatively different games, linked by the same playfield and basic rules. One or two spaceships, equipped with "Gremmarays," roam a maze of passive obstacles and explosive mines with points awarded for anything they shoot. An exploding mine will destroy anything around it, potentially setting off more mines in a chain reaction. The single player's goal is simply to get as many points as possible in the 60 or 90 seconds of playtime allotted (the present world record is 8,730), but in two player mode the players can also shoot each other for an even bigger point award. This means two-player games rapidly turn into active hunts, with a smaller bonus awarded to a player as well if the other gets nailed by a mine.

Blasto was available in both upright cabinet and flat cocktail versions, and the cocktail came in both standup and sitdown versions as appropriate for bars and restaurants. That was unusual for Gremlin games up to this time: Blockade, Hustle, Safari and Depthcharge were all strictly upright, while Comotion was strictly cocktail (sitdown and standup). The cocktail Blastos used relabeled Comotion cases but with the controls for players three and four blocked off, while the upright Blasto used the same cabinets as the other games. The difference was not merely cosmetic: only the upright Blasto could award a free game in the single-player mode if you detonated all the mines. I'll say more about that when we get to the logic board.

None of Gremlin's games were smash hits, though they certainly sold: Hustle reportedly made about a million and a half [$8.1 million] in orders, and even the inexpensively developed Blasto moved several thousand units. But Gremlin management saw something else during this period — the newly ascendant microcomputer — and they already had one in their shop to build off. Indirectly, this system led to Blasto's appearance on the TI-99/4A, though probably not in the way Gremlin would have liked.

Through newly formed subsidiary Noval, in 1977 Gremlin introduced their own microcomputer called the Noval 760 as an expansion of their internal 8080A development platform, in turn based on Hauck's original game hardware. It ran at 2.079MHz with 16K of RAM (expandable to 32K), a built-in editor and assembler in ROM, a 12" 256x224 (32x28) monochrome display, a software-controlled tape drive, 3K of programmable ROM and simple audio. Rear expansion ports allowed connecting more keyboards for two-player games, or options like an EPROM burner or papertape reader. Software such as BASIC was available on ROM or tape, and a second display or colour monitor could be fitted. However, perhaps its most arresting feature was that the computer, printer and display came permanently mounted in their own desk and popped up on springs, with a slide-out drawer for the keyboard.

Because it was based on the system Gremlin used to develop their games, which was based on the actual game hardware, the Noval 760 in theory could play those games too and was advertised as such. However, they required tweaks to run in a coin-less environment with different controls and only Blockade and Depthcharge were actually ported, with simple colour support tacked on, shown above with a screenshot of the interactive on-board assembler. Noval also produced an education-targeted system called the Telemath, based on the 760 hardware, which was briefly deployed in a few San Diego Unified elementary schools. Alas, they were long gone before we arrived.

Industry observers were impressed by the specs and baffled by the desk. Although the base price of $2995 [about $16,300] was quite reasonable considering its capabilities, you couldn't buy it without its hulking enclosure, which made it a home computer only to the sort of people who would buy a home PDP-8. (Raises hand.) Later upgrades with a Z80 and a full 32K didn't make it any more attractive to buyers and Noval barely sold about a dozen. Some of the rest remained at Gremlin as development systems (since they practically were already), and an intact upgraded unit with aftermarket floppy drives lives at the Computer History Museum.

The failure of Noval didn't kill Gremlin outright, but Fogleman was concerned the company lacked sufficient capital to compete more strongly in the rapidly expanding video game market, and Noval didn't provide it. With wall game sales fading fast and cash flow crunched, the company was slowly approaching bankruptcy by the time Blasto hit arcades. At the same time, Sega Enterprises, Inc., then owned by conglomerate Gulf + Western (who also then owned Paramount Pictures), was looking for a quick way to revive its failing North American division which was only surviving on the strength of its aggressively promoted mall arcades. Sega needed development resources to bring out new games States-side, and Gremlin needed money. In September 1978 Fogleman agreed to make Gremlin a Sega subsidiary in return for an undisclosed number of shares, and became a vice chairman.

Sega was willing to do just about anything to achieve supremacy on this side of the Pacific. In addition to infusing cash into Gremlin to make new games (as Gremlin/Sega) and distribute others from their Japanese peers and partners (as Sega/Gremlin), Sega also perceived a market opportunity in licensing arcade ports to the growing home computer segment. Texas Instruments' 99/4 had just hit the market in 1979 to howls there was hardly any software, and their close partner Milton Bradley was looking for marketable concepts for cartridge games. Blasto had simple fast action and a good name in the arcades, required only character graphics (well within the 9918 video chip's capabilities) and worked for both one or two players, and Sega had no problem blessing a home port of an older property for cheap. Milton Bradley picked up the license to Hustle as well.

TI Blasto bears a 1980 copyright date but came out in 1981 alongside the TI Hustle port. Both worked with the modestly upgraded 99/4A, and both were ultimately to become the only official home releases of any pre-Sega Gremlin game, Blockade and Depthcharge on the doomed Noval 760 notwithstanding. As was their practice at the time, Texas Instruments sold it directly as a first-party Command Module — internally an 8K GROM (TI's perverse serial ROMs) written in its mid-level Graphics Programming Language — though Milton Bradley retained the copyright.

To add greater variety in home play, the game provides a substantial number of options for both single and two-player modes, as well as a simple musical soundtrack. The port was started by MB programmer Elaine Henshon, though it was later handed off to Bob Harris for completion, and TI house programmer Kevin Kenney wrote some additional features.

For reasons unclear to me the Milton Bradley port moved from ships in a stark outer space minefield to tanks on a green Earth-bound one, possibly to emphasize the 99/4's colour graphics, and used a different bright blue logo. Nevertheless, the gameplay is otherwise the same as the arcade original and this was the version I encountered briefly in the classroom in 1982.

TI produced three variants of Blasto, all with the same SKU (PHM 3032) and all differing only cosmetically: the original black Command Module, at left, and then a red-labeled black and later beige version with refreshed packaging. Here they are with my original owner's manual, which we will of course be referring to liberally. (If you don't have the schematics for it, you don't really own it. Demand better from your hardware.)

And finally here we are with our original game board, or what Gremlin calls the video logic board (VLB).

Let's start with a basic physical inspection. Not a guarantee with random shippers, but everything seems to be intact. There are no suspiciously broken leads that would indicate a component snapped off, no rust on the contacts, and no visible damage to the board or the chips. No components appear to be removed (other than those that weren't ever mounted on this board according to the schematic). There are a couple of small jumpers in two unpopulated pads and a longer jumper on the centre right/eastern side between E4 and E5. These are factory-installed and I'll talk about them presently. The board traces look otherwise smooth except for a bit of solder rework on the centre left/western side near the edge. Some of the traces are fatter and this is a nice visual indicator to show what goes back to the PCB's great big ground plane.

Most of the capacitors are ceramic disc-style which would be fairly typical for the era. These rarely ever fail and if they do, they don't leak corrosive schmutz all over the place like blown electrolytics. There are also some small square grey film capacitors, mostly in the southwest/lower left corner, which also infrequently fail. Apart from those, I counted only a handful of smallish axial electrolytic capacitors scattered over the board plus a couple medium-sized yellow cans on the lower half. While visual inspection alone is never sufficient with these, there was no obvious leakage or discolouration and they looked to be intact. Though even a clod like your humble narrator could probably replace them if the need arose, my personal history is to cause more damage than I repair, so I left them alone. I look forward to the venomous comments of disagreement.

Across the top/north edge and in smaller blocks along the sides are the pin headers where the various harness connectors plug in. In general I/O pins are on top/north, power and sound are in the southwest/lower left corner and the video connector is in the southeast/lower right. For I/O the original Blockade has three blocks of ten pins, numbered 11 to 40, while Comotion, Hustle and Blasto have four blocks of ten pins numbered 1 to 40 (obviously some thought was given to using the same PCB as much as possible). The power header is also a 10-pin block and the audio and video headers are 4-pin. Oddly, the manual doesn't say anywhere what the measurements are, so I checked them with calipers and got a pitch of around 0.15", which sounds very much like a common 0.156" header. I ordered a small pack of those as an experiment.

I also looked at the backside and saw good clean solder joins and unbroken traces. The swooping smooth curves indicate this board, again typical for the era, was hand-routed. They don't make 'em like this anymore.

Looking closer at the front board markings, this board is ©1976 Gremlin, making it (along with my stable of MOS and Commodore KIM-1s) among the oldest systems in my personal collection. That copyright date is consistent with Comotion, because Blasto was made on a Hustle board which was derived from Comotion. Near as I can tell the PCBs are identical between those three games and they only differ in ROMs and chips on board. Blockade, on the other hand, has a slightly different setup for the ground plane.

The way you distinguish them is the assembly number, which here is delightfully hand-inked. Unlike most arcade boards where cocktail or upright mode is selected by DIP switches or the wiring harness, Blasto cocktail boards (assy. 819-0001) have different ROMs than the uprights (819-0026). This is 819-0026, so it's an upright, and the sequential nature of Gremlin's assembly numbers suggests that the cocktail was developed first. I'll discuss those differences in a moment.

The cabinets themselves have other differences: cocktail Blasto is played with directional buttons and has two external lamps for illumination, while upright Blasto is played with joysticks that actuate "snap acting" (leaf-style) switches wired to the same lines. However, neither of these differences is relevant to the VLB or reflected in the ROMs. (For comparison, Blockade's VLB is 807-001, Comotion is 808-0001, Hustle is 813-0001, Safari is 815-0001 and Depthcharge is 814-0002 because of the control changes: if you have an 814-0001, then you have a prototype. The MAME driver makes reference to an Amutech Mine Sweeper which is a direct and compatible ripoff of this board — despite the game type, it's not based on Depthcharge.)

There are six ROMs on Hustle-Comotion-Blasto boards (Blockade has just four), all of them the socketed chips in this picture. The four chips labeled 316-0095M through 316-0098M contain the game code, each 1024x4 MMI 6353-1J tri-state bipolar one-time-PROMs in ceramic casings (J). Each pair provides their respective nybbles to equal 1K bytes, and all four yield 2KB total. MMI stands for the grandiosely-named Monolithic Memories, Inc., a major early manufacturer of PROMs, PLDs and discrete logic founded in 1969 by former Fairchild engineer Ze'ev Drori. MMI was sold to AMD in 1987; their former programmable logic division is now part of Lattice. Drori was later president and CEO of Tesla Motors from 2007-8 until Elon Musk took over.

The other two bipolar PROMs are located apart from the game code because they serve a different purpose. Blockade's character generator could create one of 32 different shapes from a 5-bit value selected from two 256x4 PROMs (probably MMI 6301-1s or similar). For Hustle and Comotion, Hauck added another bit to equal six and double the characters available, and Blasto uses the same setup (two 512x4 MMI 6306-1J tri-state bipolar one-time-PROMs). These are labeled 316-0099M and 316-0100M.

The cocktail has lower-numbered ROMs (again evidence it was developed first), 316-0089M through 316-0094M. Its character PROMs have glyphs for TIME and the digits for 0-9 in two orientations, plus glyphs for GAMEOVR and the spaceships, mines, explosions and Gremmarays, and its code PROMs will select the correct orientation based on who is playing where. The upright naturally has just one orientation, so in place of the secondary orientation it adds almost a full set of uppercase letters instead. These are used to maintain a single player high score as well as support the free game feature if the single player destroys every mine in time, neither of which is supported on the cocktail. This feature could be jumpered off if free games were illegal in your jurisdiction, which was also a problem for pinball at the time. Interestingly, the ROMs inventoried by the current MAME driver are listed with the part numbers for the cocktail, but the ROM contents expected in the hashes actually correspond to the upright.

Bipolar ROMs and PROMs are, as the name suggests, built with NPN bipolar junction transistors instead of today's far more common MOSFETs ("MOS transistors"). This makes them lower density but also faster: these particular bipolar PROMs have access times of 55-60ns as opposed to EPROMs or flash ROMs of similar capacity which may be multiple times slower depending on the chip and process. For many applications this doesn't matter much, but in some tightly-timed systems the speed difference can make it difficult to replace bipolar PROMs with more convenient EPROMs, and most modern-day chip programmers can't generate the higher voltage needed to program them (you're basically blowing a whole bunch of microscopic Nichrome metal fuses). Although modern CMOS PROMs are available at comparable speeds, bipolars were once very common, including in military environments where they could be manufactured to tolerate unusually harsh operating conditions. The incomparable Ken Shirriff has a die photo and article on the MMI 5300, an open-collector chip which is one of the military-spec parts from this line.

The 8080A CPU here is, amusingly, manufactured by Texas Instruments as a second source (TMS8080ANL). I find this particularly funny because my two Texas Instruments Silent 700 teletypes, both my Model 745 KSR and bubble memory Model 763 ASR, use AMD 8080s! The Intel 8080A is a refined version of the original Intel 8080 that works properly with more standard TTL devices (the original could only handle low-power TTL); the "NL" tag is TI's designation for a plastic regular-duty DIP. Its clock source is a 20.79MHz crystal at Y1 which is divided down by ten to yield the nominal clock rate of 2.079MHz, slightly above its maximum rating of 2MHz but stable enough at that speed. The later Intel 8080A-1 could be clocked up to 3.125MHz and of course the successor Intel 8085 and Zilog Z80 processors could run faster still. An interesting absence on this board is an Intel 8224 or equivalent to generate the 8080A's two-phase clock: that's done directly off the crystal oscillator with discrete logic, an elegant (and likely cheaper) design by Hauck. The video output also uses the same crystal.

Next to the CPU are pads for the RAM chips. You saw six of them in the last picture under the second character ROM (316-0100M), all 2102 (1Kbit) static RAM. These were the chips I was most expecting to fail, having seen bad SRAM in other systems like my KIM-1. The ones here are 450ns Fairchild 21021 SRAMs in the 21021PC plastic case and "commercial" temperature range, and six of them adds up to 768 bytes of memory. NOS examples and equivalents are fortunately not difficult to find.

Closer to the CPU in this picture, however, are two more RAM chip pads that are empty except for tiny factory-installed jumpers. On the Hustle and Blasto boards (both), they remain otherwise unpopulated, and there is an additional jumper between E4 and E5 also visible in the last picture. The Comotion board, however, has an additional 256 bytes of RAM here (as two more 1024x1 SRAMs). On that board these pads have RAM, there are no jumpers on the pads, and the jumper is now between E3 (ground) and E5. This jumper is also on Blockade, even though it has only five 2102s and three dummy jumpers on the other pads. That said, the games don't seem to care how much RAM is present as long as the minimum is: the current MAME driver gives all of them the full 1K.

With our cursory visual survey complete, our next order of business is to figure out how to power this thing, so we'll start with the CPU. Unlike, say, the 6502 which can run on a single +5 volt supply (as can the 8085 and Z80), the 8080 and 8080A require multiple voltages, which again was not unusual for contemporary processors. The schematic showed +5V coming from pins 41, 42 and 43, ground from 45, 46 and 47, +12V from 49, and further up -12V from pin 50. The -12V line goes through a simple voltage divider to generate the -5V the processor actually wants (compare with this 8080 system which uses a regulator). Tracing the schematic out further, the -12V line is also used with the +5V and +12V lines to run the video circuit. These are all part of the 10-pin power header.

To check my work, I then consulted the wiring diagram for the video logic board and the power supply board, since we don't have the original power supply. This got a little confusing: the schematic says power supply pins 18, 19 and 20 should all be +5V, going to pins 43, 42 and 41 on the VLB, but the cabinet wiring sheet claims that pin 20 (41) on the power supply is tied to ground. At this point I had to follow the traces myself to figure out which one was right. The power header has a big "finger" going into the ground plane around the edge of the board, but not for any of those three pins (note that this "finger" is absent on Blockade and the ground plane looks a bit different). In addition, both the schematic and my continuity tester showed pin 41 was going to the processor's +5V line (CPU pin 20), so I concluded the wiring diagram was wrong. The multiple grounds and the two 12-volt lines all matched up.

I tallied up everything on paper. We have a 10-pin power block that goes (starting with pin 41) +5V, +5V, +5V, key pin (removed), ground, ground, ground, key, +12V, -12V. The little 0.156" header pack arrived and it fit (so I ordered some more).

Now, what fits a 0.156" pitch and almost this exact sequence of voltages? An AT power supply connector! If we're clever about how we put the two halves on, we can get nearly the right lines in the right places. The six-pin AT P9 connector reversed is +5V, +5V, +5V, -5V, ground, ground, so we can cut the -5V to be the key. The six-pin AT P8 connector not reversed is power-good, +5V (or NC), +12V, -12V, ground, ground, so we cut the +5V to be the key, and cut the power-good line and one of the dangling grounds and wire ground to the power-good pin. Fortunately I had a couple spare AT-to-ATX converter cables from when we redid the AT power supply on the Alpha Micro Eagle 300.

Because the power header is only keyed in the sense that a couple pins are clipped off, the AT power connectors will fit in pretty much any orientation. That's convenient and also runs the risk of frying our board if we install it wrong, so I decided to also key the connectors since we're going to modify them anyway. A quick couple drops of light-cured cyanoacrylate into the key hole ...

... and light exposure from both directions will make a nice hard cap in that location so that it can't go in over a live one without a lot of force.

Six lines down, four to go.

The first thing to do is clip the lines we won't be using, at least not for the connector (we may use the power-good line for something else in the future, but I'll talk about that soonish).

However, since these are both 6-pin connectors and the power header is 10-pin, we're out of space.

But since they're just ground and unconnected to the Blasto board anyway, we'll clip them and then shave off the overhang in the workshop.

This fits and leaves enough space for the sound connector, which we'll get to a little later.

Last but not least, we take one of the ground wires we clipped off and solder that to the pin for known-good so we have all our ground lines up. Because the orientation of the AT connectors is different, I keyed this connector too and marked both halves of the power connector with "IN" for good measure to indicate the side that should face IN to the board components. There's always one more idiot than you counted on, but in this case the idiot is me, so this should make it a little more me-proof.

I connected the modified AT-to-ATX converter up to a cheapo off-the-shelf 500 watt ATX power supply which is waaaay overkill for this but it was sitting around doing nothing, so it can henceforth be dedicated to Blasto gaming. Taping the switch lugs together to force power on, I verified the PSU with a tester, then checked voltages and ensured everything matched up with the schematic and wiring diagram. It's time for the moment of truth.

Something's alive! An LED glows! Time now for the video connector to see if we can get a picture!

The service manual calls the display "a standard 525 scanline system," which I interpret as NTSC 59.97Hz composite video, and is the display type for all of these related games. Returning to the schematic, a whole bunch of components and discrete logic incorporating a line labeled VBLANK eventually terminate at pin 58 (southeast corner/lower right) with 57 keyed no-connect and 56 and 55 to ground. That sure sounds like a composite connection. My box of additional 0.156" connectors hadn't arrived yet, so I used the other 6-pin connector in the package for this 4-pin connector (there's plenty of space), inserted wires for signal and ground, and keyed and labeled the proper orientation.

For the other end I got back out the soldering iron and put an RCA phono jack on those pins. We'll use the front jacks on my trusty Commodore 1702 video monitor as the composite display, the best JVC monitor Commodore ever rebadged.

Powering it back up with the 1702 connected and adjusting the vertical hold, we get a stable picture, but it sure doesn't look like our game. Back to the service manual.

The troubleshooting procedures conveniently have a section for "meaningless display on screen." It advises checking the four game ROMs and then a so-called "power interrupt board" connected to test points 3 and 4. We already physically inspected the PROMs, but I reseated them anyway just in case, and nothing changed.

Putting aside for a moment the possibility the PROMs could be bad, I examined the manual's schematic for the power interrupt board, which of course we don't have. This board connects to direct A/C input (via the transformer), the power supply board for +5V and -12V, an antenna lead (wired to the coin box), and those two test points. The way the two 555 timers are daisy-chained together suggests that when the power comes on (with -12V wired to the first one's reset), a brief signal is triggered and then extinguished, during which test point 3 is pulled to ground (i.e., test point 4) and then released.

And where does test point 3 go? It goes ... to the CPU reset line. The 8080A can't bootstrap itself automatically when power is applied and neither could many chips of that time; it needs to have its reset line driven low to start it up when power is applied (for example, here's a nice 6502 reset circuit).

The board does have its own reset circuit, of a sort. You'll notice here that the coin start is wired to the same line, and the manual even makes reference to this ("The circuitry in this game has been arranged so that the insertion of a quarter through the coin mechanism will reset the restart [sic] in the system. This clears up temporary problems caused by power line disturbances, static, etc."). We'll of course be dealing with the coin mechanism a little later, but that doesn't solve the problem of bringing the machine into the attract mode when powered on. I also have doubts that people would have blithely put coins into a machine that was obviously on the fritz.

Indeed, TP4 on the board is on one of those nice fat ground traces. The test points are the same sorts of pins as on the headers, so I connected some wires from the header kit to TP3 and TP4 and shorted them briefly and ...

... it comes up in the attract mode, ready for action! The picture is a little too big for the screen, but this can be adjusted. (I also noticed that the LED went out at the same time, which might be a useful debugging clue.) We can now be fairly well assured that the CPU, PROMs and at least a good portion of the RAM are in good nick. Now we need to wire up the rest of the harness and try to actually play it.

While I went through the wiring diagrams and wrote up what goes where, I also put a proper power switch on the AT-to-ATX converter so I didn't have to keep the switch lugs shorted to turn it on (AT power supplies have an integral switch). This can be done by prying open the switch lugs on the converter and worming them onto the switch's contacts, here a classic "clicky" push-button.

With that settled, the business end is naturally in those four 10-pin headers across the top. Fortunately my box of additional connectors and wires had arrived, including 10-pin ones, so now we have plenty. The idea is to connect two regular Atari joysticks, preferably without having to modify those too, plus any other switches we'll need.

The first step is to install, key and label the orientation of each 10-pin connector, and I also went ahead and stuck ground wires in as useful landmarks since we'll be using common grounds a lot here. Blockade obviously lacks pins 1-10, but the wiring diagrams for Blockade and Comotion also both lack ground on pin 38, which may be an error since Hustle and Blasto do have ground there. The grounding points are otherwise the same on all four boards. (I should note that if you're using this article to wire up a non-Blasto board, I'd check your manual's diagram carefully to make sure I haven't missed anything — I'm not responsible for you frying your rare arcade treasure.)

The joystick leads are in fact what are called the player control buttons. These are indeed truly buttons on the cocktail, but the same lines are where the leaf switches for the joysticks on the upright connect also. The wiring diagram page also has a schematic of the switches as viewed from the underside of the control panel, so we need to flip it left to right to get the correct pin assignments, showing that ABCD are the directional controls for player 2 (pins 1, 2, 4 and 5) and EFGH are for player 1 (pins 7, 8, 9 and 10), with ground in the middle and a single key pin. I wired these up and bundled them, marking the player 1 wires with a Sharpie. The fire buttons and the 1 and 2 player start buttons, however, are wired separately to the 21-30 block.

Comotion, by contrast, puts players three and four on the 1-10 block and players one and two on 21-30. It has no fire buttons, only a single start button, and a selector for three or four arrows, both on 31-40. Hustle and Blockade also put both players on 21-30 and have no fire buttons. However, Hustle has separate 1 and 2 player start buttons on 31-40 and uniquely uses 1-10 to determine the rules for free games, while Blockade has no start buttons at all (game play starts on coin in) and uses pins 32-36 to determine the play-to score. Bottom line is check the wiring diagram if you're hooking up one of these because Blasto is a bit different.

What we don't know yet is which leaf switch goes which way. We can guess which pair is up and down, or left and right, but not which one is exactly which because that depends on the joystick construction. We'll come back to this.

For the 21-30 block I used orange wires for fire and yellow wires for start. Fire 1 (J) is on pin 30, fire 2 (I) on pin 21, and the start buttons on pins 28 and 29 (1 and 2). I marked player 1's wires with a Sharpie here too.

On all four boards are leads for a coin counter between pins 14 and 20. A coin counter is exactly what you think it is: a rolling counter that keeps track of how many coins have been inserted for the operator. In early games like this one, the counter was mechanical, not unlike a handheld tally counter. Every time a coin is inserted, a pulse is sent and the counter goes up by one. The manual says a 10K resistor between these lines will enable normal operation without an actual coin counter installed, so I did so. This is in fact required for the coin reset circuitry I mentioned previously to work.

Although there are jumpers for controlling whether a free game is awarded (pin 33 to ground) and enabling more play time (pin 32 to ground), there is no way to jumper this board for free play, so we'll have to fake up the signals for a coin box. This is a pair of switches in the 31-40 block in which pin 40 is normally closed to ground (pin 38, listed only as "common" on Blockade and Comotion) and pin 37 is normally open. When a coin is inserted, the normally-open switch briefly closes at the same time the normally-closed switch opens, after which the normally-closed switch recloses as the normally-open switch reopens.

We can fake this out by shorting the normally closed wire to ground, then quickly separating it and touching the normally open wire to ground. It takes a little practice to time it right, but with a little fiddling we can make the board think there's a coin there ("PRESS START"), so that logic works too.

We then short the player 1 start wire to ground and the one-player game comes up ("HIT ALL MINES FOR FREE GAME").

Doing great so far, but it's a bit inelegant to be shorting multiple different wires to reset the board, "insert" a coin and "press" start, so let's install some switches now, starting with the coin wires. For this application we'll use a simultaneous momentary on-momentary off button, where normally-closed is closed and normally-open open when the button is not pressed, but normally-closed is opened and normally-open closed when the button is, all at the same time. Pressing it and releasing it will thus look to the board like a coin was inserted. It has contacts for common, normally-closed and normally-open, so we just solder the correct wires to the correct contacts.

Here's the switch installed, and I also put a proper button between TP3 and TP4 at the same time.

Now, after power-up, a click of the test point button resets the CPU and starts attract mode, and a click of the coin button will "insert" a coin. Theoretically you could just insert a coin and trigger the reset directly, but I like this way better.

Next, the joysticks and start buttons. Again, for the joystick, it depends on how the joystick moves within its enclosure and its orientation relative to the switches as to how the switches get hit. I couldn't obviously tell from this diagram how it moved, so I took a guess that it tilted on a fixed axis and would hit the switch on the opposite side. (NARRATOR: They don't.)

With that in mind, I bought a pair of male DE-9 ("DB-9") cables with ready-to-solder ends that any Atari joystick can plug into. Classic Atari sticks, including those used by Commodores and Amigas, work by simply grounding the line corresponding to up, down, left, right or fire. This board also expects the appropriate directional line to be grounded, so that's exactly what we'll do.

Obnoxiously, there aren't enough grounds on the top header block to make this easy. The 1-10 block has only one ground for both players and the 21-30 block has only one ground for both start buttons. Also, because the fire buttons are separated, I didn't want to have to solder the joystick cables across multiple blocks since that would make it more difficult to remove the connectors without yanking something.

Instead, I added a "floating" pin header and soldered both fire wires (FireWire! nyuk nyuk nyuk) to one end of the header, and then slid two more orange connecting wires on the other like I used for the test points so that they could easily be removed. The joystick cables can then be connected to those and detached without desoldering or cutting anything. Onto another pin on the floating header I also soldered the single ground and then split it from there to the player 1 and player 2 start buttons soldered to the yellow wires. This ground can then be used for player 1 with another header-connecting wire, and player 2 can use the ground on 1-10.

For the first test I wired up a port with the fire button, plus what I thought was up and what I thought was left (so if I was wrong, I only had to redo two wires), and plugged in one of my Atari CX40 sticks.

The fire button worked great. The up and left directions also worked great — if your intention was to move down and right. My guess was wrong; the switches are hit in the same direction.

Back to the soldering iron to desolder and redo the connections properly this time.

In the end the wiring schedule for the directional switches looks like this (again, Blasto-specific): up is on pins 5 (2P) and 10 (1P), left is on pins 4 and 9, down is on pins 2 and 8, and right is on pins 1 and 7. Connect these to your standard Atari joystick port pinout (on the male side 2, 4, 1 and 3 respectively, with ground on 8 and fire on 6). Once I confirmed both sticks were working, I then bundled the bunch of wires between the ports and the headers together and zip-tied each end of the bundles to make it nicer looking and add a bit of strain relief.

The last step is the audio cable. On the real machine there is an amplifier (as part of the power supply) and a volume control, though the 1702 has an amplifier and volume control too, so simply wiring it in and cranking up the volume should be enough to at least hear something. It has specific circuitry to generate a "boom" sound on explosions which on the Blasto and Comotion boards can be specifically disabled, but where's the fun in that? The audio connector is the little four-pin deal under the power header, with ground on pin 51 and signal on pin 53, so I put another RCA phono jack there.

The audio effects aren't loud, which was expected, but the sound is still perfectly audible. It's time for the final playtest.

The free game logic works in the single player mode.

And my wife finally won a game in the two player mode.

We now have an overgrown Blasto direct-to-TV games system which to all appearances is fully functional. Almost disappointingly, I can't find any flaws in it. Despite the fact it was sold as a bare untested board, it seems to play absolutely perfectly, though there was no way to know that until we finished hooking it all up.

Before we close, a few last tidbits on the fate of Gremlin. In 1982, Gremlin moved into a larger manufacturing facility in north San Diego's Rancho Bernardo and was renamed to Sega Electronics, Inc. (distinct from Sega Enterprises) to emphasize the brand name more strongly. The company entered a rapid decline with the video game crash of 1983 and the manufacturing assets were sold to Bally Midway with certain publishing rights, but the original Gremlin IP and game development teams stayed with Sega Electronics and remained part of Gulf+Western until they were disbanded. The brand is still retained as part of CBS Media Ventures today though modern Paramount Global doesn't currently use the label for its original purpose. In 1987 the old wall game line was briefly reincarnated under license, also called Gremlin Industries and with some former Gremlin employees, but only released a small number of new machines before folding. Meanwhile, Sega Enterprises separated from Gulf+Western in a 1984 management buyout by original founder David Rosen, Japanese executive Hayao Nakayama and their backers. This Sega is what people consider Sega today, now part of Sega Sammy Holdings, and the rights to the original Gremlin games — including Blasto — are under it.

Lane Hauck's last recorded game at Gremlin/Sega was the classic Carnival in 1980 (I played this first on the Intellivision). After leaving the company, he held positions at various companies including San Diego-based projector manufacturer Proxima (notoriously later merging with InFocus), Cypress Semiconductor and its AgigA Tech subsidiary (both now part of Infineon), and Maxim Integrated Products (now part of Analog Devices), and works as a consultant today.

I'm not done with Blasto. While I still enjoy playing the TI-99/4A port, there are ... improvements to be made, particularly the fact it's single fire, and it was never ported to anything else. I have ideas, I've been working on it off and on for a year or so and all the main gameplay code is written, so I just have to finish the graphics and music. You'll get to play it.

And the arcade board? Well, we have a working game and a working harness that I can build off. I need a better sound amplifier, the "boom" circuit deserves a proper subwoofer, and I should fake up a little circuit using the power-good line from the ATX power supply to substitute for the power interrupt board. Most of all, though, we really need to get it a proper display and cabinet. That's naturally going to need a budget rather larger than my typical projects and I'm already saving up for it. Suggestions for a nice upright cab with display, buttons and joysticks that I can rewire — and afford! — are solicited.

On both those counts, to be continued.