Path: news.spies.com!genmagic!sgigate.sgi.com!swrinde!newsfeed.internetmci.com!chi-news.cic.net!news.math.psu.edu!hudson.lm.com!asia.lm.com!not-for-mail From: essayes@telerama.lm.com (David Shuman) Newsgroups: rec.games.video.arcade.collecting Subject: Sega XY on Atari monitor: it works! Date: 3 Jan 1996 16:32:11 -0500 Organization: Telerama Public Access Internet, Pittsburgh, PA USA Lines: 216 Message-ID: <4ceskr$ajn@asia.lm.com> NNTP-Posting-Host: asia.lm.com The good news is, it can be done. The bad news is, it isn't perfect, at least not yet. SEGA-TO-ATARI VECTOR MONITOR ADAPTER by David Shuman mappy@virginia.edu, essayes@telerama.lm.com 3 January, 1996 DISCLAIMER AND WARNING The author disclaims any and all responsibility for damage and injury directly or indirectly caused by the use of the information contained in this document. Procedures for modifying game and monitor circuitry must be performed carefully and at the reader's own risk. OVERVIEW This hack allows you to play Sega XY (vector) games (Eliminator, Space Fury, Star Trek, Tac/Scan) on an Atari color XY monitor. Sega XY games originally came equipped with the Electrohome G08 color vector monitor. Both the first incarnation of this monitor, the G08-001, and its replacement, the G08-003, were notoriously unreliable, and were the primary reason most Sega XY games quickly ended up in landfills. The records of the Video Arcade Preservation Society show that these games are rare even among collectors, no doubt due mainly to the scarcity of working monitors. John Grigsby said it best when he remarked, "Sega vector games are like British sports cars-- they're great when they work." Though the Atari color XY monitors were also infamous among operators for their frequent failures, these monitors perform adequately well when not subjected to constant use. Atari color vector monitors are far more common than their Sega counterparts; it is likely that far more Atari units were manufactured, and that fewer of them succumbed to the catastrophic (often firey) failures that sent thousands of Sega XY games to their graves. Compared to the Electrohome G08, the Wells-Gardner 19K6101 monitors are extremely reliable and easy to repair. Zanen Electronics sells a "Get Well Kit" that provides a quick fix for most problems with the W-G, and Gregg Woodcock's Atari XY FAQ offers an exhaustive review of failures and fixes. By contrast, no commercial kits are available to rehabilitate the G08, and no FAQ exists to aid in its repair (at least not yet). Complete schematics for the most common version of the of the G08-003 are difficult to find. Finally, unlike the W-G, the G08's circuit boards are not connectorized, so even removing them from the chassis for testing and repair can be extraordinarily frustrating. Owners and would-be owners of Sega XY hardware have always known that these games would be much easier to acquire and keep running if they could be interfaced to the Atari XY monitor, but, at least on rec.games.video.arcade.collecting, no one has ever described exactly how this feat might be accomplished. It appears, however, that the mystery may at last have been solved. This hack was developed and tested using a W-G 19K6101 monitor with the 31X series boards supplemented by an original Atari Input Protection Circuit PCB. I see no reason why the adapter would not work equally well without the IPC or on a 32X or 33X series monitor. THEORY Many collectors have played Atari vector games on an oscilloscope in XY mode, and know that a color vector monitor is just an o-scope with three color guns. Both the G08 and Atari XY monitors have inputs for X deflection, Y deflection, red, green, blue, and ground. How different could they be? Not surprisingly, they're very nearly alike, at least in terms of their operating parameters. The biggest difference is that the W-G and Amplifone have different deflection ranges than the G08: according to the manufacturer's specifications, the Atari system uses -12 to +12 VDC for X deflection, and -8 to +8 VDC for Y deflection; the Sega system uses -4 to +4 VDC for X and -3 to +3 VDC for Y. Why not just plug the X and Y outputs from the Sega game boards into the X and Y inputs of the Atari monitor? You could, if you could live with the shrunken picture, but if you're using an original Sega G-80 power supply, you'll eventually blow the 7905 -5 VDC regulator. The reason for this failure is probably that the input impedances for the X and Y signals are slightly different for the G08 than for the W-G, and the vector generation circuits on the game boards wind up drawing too much power. (The G-80 power supply itself is flaky at best, and should be replaced with a modern switching power supply.) DESCRIPTION The conversion circuit is constructed around the TL082 op-amp (the dual version of the TL081). This chip acts both as an amplifier, to boost the voltage of the Sega video outputs, and as a buffer, to isolate the game boards from the monitor and match impedances. The device is configured as a pair of non-inverting amplifiers (one for each axis), each of which accepts the deflection signal from the game board, amplifies it, and outputs it to the monitor at a voltage that produces a full-size image. The conversion also requires a minor modification to the spot killer circuitry of the W-G monitor. Without this alteration, the spot killer will partially activate during screens where few vectors are displayed, distorting the picture. Adding a pair of capacitors effectively reduces the sensitivity of the spot killer so that it won't be triggered when it shouldn't be. A real failure condition, in which the X and Y inputs fall to zero, still deactivates the beam immediately, preventing damage to the phosphor coating. The alterations to the spot killer do not affect the monitor's ability to properly display Atari XY games. CONSTRUCTION Using two 1/4 W 2.2K resistors, two 1/4 W 3.3K resistors, and two 10K potentiometers, construct two non-inverting amplifier circuits using the schematic crudely reproduced below. The drawing shows the configuration for the X axis; the Y axis circuit is identical. +Vcc | ...| 2.2K | \ Xin ---RRR---|+ \ | :----+------ Xout +--|- / | | | / | | |..| | | | | | -Vcc R +----------->R 10K pot R | | R R 3.3K R | | gnd The adapter works reasonably well using either two 741 op-amps or one TL082 op-amp. Other chips may work better; please experiment if you have the opportunity. Pinout of the TL082: 1 out #1 5 in(+) #2 2 in(+) #1 6 in(-) #2 3 in(-) #1 7 out #2 4 -12 VDC 8 +12 VDC Pinout of the 741: 1 5 2 in(-) 6 out 3 in(+) 7 +12 VDC 4 -12 VDC 8 During operation, the TL082 draws approximately 5 mA from both the +Vcc and -Vcc lines. It should be possible, then, to provide power for the adapter directly from the +12 VDC and -12 VDC lines of the game's power supply. In my test fixture, I have been using a switching power supply to provide the requisite voltages to the game boards, and the G-80 power supply (which remains connected as a source of 6 VAC and audio amplification) to feed the adapter circuit. To modify the spot killer circuit of the W-G monitor, you will need two 2.2 uF, 50V electrolytic capacitors. Remove the deflection board and solder these capacitors to the underside of the board in parallel with C802 and C803. Be sure to install the new capacitors with the correct polarity. The Wells-Gardner 19K6101 monitor takes power from a center-tapped 50 VAC winding on the main transformer (the "25-0-25" scheme). Note that this is a different arrangement than that used by the Electrohome G08, which draws power from a center-tapped 100 VAC winding (the "50-0-50" scheme). If you are mounting the W-G monitor in a Sega cabinet, you will need to install an extra transformer to power the monitor. If you are installing the Sega game boards in an Atari color vector cabinet, use the standard "edge connectors and fingerboard" method, incorporating the video adapter and a suitable power supply. Sega XY games use different voltages than Atari color XY games, so it may be a good idea to attach the Sega boards to a separate power supply. A small switching power supply capable of +5, +12, -5, and -12 VDC will be adequate. The +5 VDC supply should be rated at 10 A or more. Note that the original Sega G-80 power supply also produces 6 VAC for the sound board; I don't know whether the 10.3 VAC found in Atari color XY games is an adequate substitute. Experiment at your own risk. ROOM FOR IMPROVEMENT The adapter circuit works reasonably well, but not perfectly. When many vectors are displayed at once, some of them appear in the wrong place, and images become slightly distorted. Fortunately, the effect is not so great as to render the games unplayable, or even unsightly, as the distortion is often unnoticeable. If the potentiometers are adjusted so that the picture is fairly small, all vectors are displayed normally. This effect suggests that the bad vectors might result from a reduction in bandwidth as the gain is increased. The problem persists if the TL082 is reconfigured as a pair of inverting amplifiers. Though this design provides a higher slew rate than the non-inverting circuit, the source of the distortion is apparently not the configuration of the amps. The picture is no better or worse if a pair of 741's is substituted for the TL082. It may be that neither of these op-amps is entirely suitable for the task, and that some more modern device might be necessary to completely eliminate the garbled vectors. FOOD FOR THOUGHT A Space Duel cabinet would make a perfect home for Eliminator and Space Fury, as it has the same controls and accomodates two players at once. Space Fury would drop nicely into a Gravitar cabinet; so would Eliminator if you didn't mind being stuck with one-player mode only. Tac/Scan and Tempest are both vertically-oriented color XY games that use two buttons and an encoder wheel. It shouldn't be too hard (and might be very easy) to adapt a Tempest encoder wheel to play Tac/Scan, or vice versa. Maybe Tac/Scan would be easier to play with a trackball or a "roller controller" like you find in a dedicated Major Havoc. As for Star Trek, well, how about drilling a few extra holes in your Tempest control panel and dropping more buttons in there? Or adding an encoder wheel to your Gravitar control panel? Hmm. We know you can build a digital-to-analog adapter for joysticks. If you could build an analog-to-digital adapter, you could rewire a Star Wars flight controller to emulate rotate left, rotate right, thrust, and fire, and use it to play Eliminator or Space Fury. ACKNOWLEDGEMENTS Thanks to: Doug Jefferys Duncan Brown Gregg Woodcock Bryan Bazil D'Oliviero (c) 1996 David Shuman -- --Dave--