TOURING MCM DESIGN'S HI-RES ASTROCADE Version 1.0, August 23, 2018 The intent of this lengthy tour is to provide detailed info on MCM Design's low/hi-res Astrocade for anyone desiring to take the challenge and build such an Astrocade. The details may help provide ideas for creation of someone's own version of a hi-res Astrocade. Refer to photos in "Pictures/Hardware Pictures/Hi-Res Astrocade (Matte)" section at BallyAlley.com while touring this Astrocade. The URL is here: http://www.ballyalley.com/pics/hardware_pics/Hi-Res_Astrocade_Matte/Hi- Res_Astrocade_Matte.html PIC0 (Original) This Astrocade is mounted on top of a Viper1 cabinet, which houses the majority of the added circuitry allowing the Astrocade to operate in either low or high screen resolution. The low or hi-res modes are software selectable with an optional mode using an internal DIP switch, to operate strictly in hi-res. An interface allows a full size matrix keyboard to be plugged into the back of the Viper cabinet using a ribbon cable connector. The Astrocade's 24 button keypad wiring to the motherboard has been extended (hardwired) to a 14 pin wire wrap socket mounted on the bottom left side of the Astrocade's console, so that a custom modified remote 24 button keypad can be plugged into this Astrocade using a ribbon cable connector. This keypad, being at table height, is a lot easier on the hand when entering multiple bytes of data using Bit Fiddler's low or MCM Design's high-res MLM (Machine Language Monitor). The top half of the Astrocade's console was spray painted with semi-gloss black, an attempt to match the color of the Viper cabinet. This Astrocade has gone through a transition since the mid 1980's with changes here and there. In particular, the user RAM was changed from dynamic to static RAM because of its simplicity and smaller board area requirement. The user RAM documented on the Bally Alley for this Astrocade is now obsolete. An addendum to the documentation updating this Astrocade's current electronic schematics should really be posted. Cutouts were made in the sides of the Viper cabinet and covered with 3 1/4" square vent covers to facilitate an internal forced air cooling fan for the Astrocade motherboard. PIC1 The front view of the Astrocade/Viper cabinet reveals a 24pin wire wrap socket mounted on the bottom of the modified Astrocade motherboard to connect 23 necessary motherboard lines to the screen RAM interface in the Viper cabinet using a 24pin DIP ribbon cable connector. The webbed Viper eye is a power on LED indicator. PIC2 With the Astrocade console top removed, the custom audio/video board becomes visible. This WW board has a quick-connect to the motherboard. The LM1889 circuitry outputs a composite video signal. There is no RF circuitry. A 2 transistor configuration, identical to the Datamax UV-1R, is used as a driver for a TV/monitor. The LM377 audio amplifier outputs two channels. One channel will drive an 8 ohm passive speaker. The other channel is set up for connection to the audio input of a TV/monitor (or amplified speaker system). The bottom left side of the Astrocade console has the following mounted on it, left to right: 1. 14pin WW socket to plug in the remote 24 button keypad. 2. RCA phono type audio output jack for use with a TV/monitor. 3. Mini volume control for use with 5 below. 4. RCA phono type composite video output jack for use with a TV/monitor. 5. Audio 1/4" headphone jack to drive a passive 8 ohm speaker. No Photo The rear of the Viper cabinet has the following mounted on it, from left to right: 1. Two 25 pin Centronics connectors wired to the internal Z80 DART interface. 2. 120vac fuse holder. 3. Lighted 120vac power on/off switch. 4. 2000/6000H mini-toggle switch for user RAM 6000-7FFFH. 5. User RAM "write protect" mini-toggle switch for user RAM 6000-FFFFH. 6. Mini 120vac receptacle for use with an audio cassette recorder. 7. Two hinges, so the Viper ROM/RAM board assembly can be swunge up and back to facilitate troubleshooting. PIC3 To access the interior of the Viper cabinet, both Viper side panels must be removed. A 14.5 x 1/2" plastic piece must be slid out of the cabinet top. This will allow the hinged Astrocade and ROM/RAM board assembly to swing up and back gaining easy access to the Viper interior. There is a fan mounted and pointed at the bottom left of the Astrocade console attempting to force air over the motherboard and out the limited console vents/ openings. The motherboard has no metal shielding present to restrict air flow. This Astrocade has no RF circuitry, so the metal shielding can be removed with no negative effect on the TV/monitor display. The custom data chip, with its custom black heat sink, runs cooler than normal. The voltage regulator heat sinks run cooler anyway because 11 chips on the modified motherboard are no longer present. There is a purchased +5v,+12V,-5VDC power supply board to power the ROM/RAM board. The required -5VDC for the 4 banks of dynamic screen RAM can be tapped from the motherboard if desired. The -5V current draw for the 16KB screen RAM is very low. To the back right, inside the Viper cabinet, is the interface for the full size matrix keyboard, which is not being used presently. PICS 4 AND 5 Two ribbon cables are plugged into the ROM/RAM board. The bottom cable comes from the Astrocade motherboard 50pin expansion. The top cable comes from a 24pin socket mounted on the bottom of the motherboard. The PX, system I and 7M clocks plus Z80 address lines A0 and A1, for the screen RAM interface, come from the 50-pin expansion. A better choice may be to utilize a 28pin ribbon cable connection from the motherboard to the ROM/RAM board instead of splitting all 28 lines necessary to operate screen RAM. In this case, you wouldn't even need the 50pin expansion cable to run screen RAM. To the upper right are the four 4KB banks of dynamic RAM required to operate in hi-res. Only one bank is necessary for low-res. To the left are four 74LS253 chips to select the appropriate bank for a Z80 hi- res read in which case one of the four banks is selected using the Z80 address lines A0 and A1. A low-res Z80 read will select only 1 specific bank. To the left of those four chips are four 74LS166 chips used to receive all 32 RAM data out bits for the hi-res video scan, which are then transmitted to the custom data chip serial 0 and serial 1 inputs. The chips to the left of the 74LS166 chips are used as timing control signals, buffers, selectors and other duties for low or hi-res modes. Some of the chips at the bottom left are also used for the screen RAM interface. The trimmer pot to the left is used to adjust the RAS line. Once set for low and hi-res modes, this trimmer should really be replaced with a resistor, if possible. Aging trimmers tend to create problems. The screen RAM interface used is similar to the Datamax UV-1R scheme. Only one RAS line is wired to all four RAM banks with the four lines CAS0, CAS1, CAS2 and CAS3 acting like bank selects. To the bottom right is the Z80 DART circuitry which is not being used presently. To the left of the DART and its interface are three 28pin sockets. The right socket is Z80 addressed for 32KB at 8000-FFFFH. Up to a 32KB static RAM chip or compatible EEPROM can be used in this socket. The center 28pin socket is Z80 addressed for 8KB at 6000-7FFFH and is switchable to 2000-3FFFH using a mini-toggle switch mounted at the rear of the Viper cabinet. Up to a 32KB static RAM chip or compatible EEPROM can be used in this socket. This socket is "multi-carted" for four 8KB banks using 2 DIP switches located near this socket. When the Astrocade is running in the hi-res mode, this socket will be disabled, unless it is switched to 2000-3FFFH. A mini-toggle switch mounted at the rear of the Viper cabinet will "write protect" both the center and right 28pin user RAM sockets. The left 28pin socket will be used for an 8KB hi-res ROM (EEPROM) addressed 0000-1FFFH and loaded with a hi-res conversion of the low-res UPI/on-board subroutines, additional fonts plus about 4KB containing an extended UPI (EUPI) with custom graphic subroutines. This hi-res ROM, when selected with one DIP switch, will allow the Astrocade to run strictly in the hi-res mode. Manually making this selection will also disable the low-res ROM on the Astrocade motherboard. To the left of the three 28pin sockets are the necessary hi-res ROM and user RAM interfacing chips. Some of these chips are used for screen RAM duties. There is a second 50pin ribbon cable expansion header for use with BalcheckHR or other remote PC/WW boards. To the upper left on the ROM/RAM board are quick-connect power supply connectors and hard wire solder contacts. The rectangular metal cutout on the left is where the horizontally mounted cooling fan in the Viper cabinet directs forced air into the Astrocade console in an attempt to dissipate generated heat inside the console and out its limited air vents/openings. The ROM/RAM board was wire wrapped in the mid 1980's. All of the 0.1uf decoupling disk capacitors plus additional tantalum capacitors wired to the +5V,+12V and -5V power supply connections were soldered to the bottom tips of the wire wrap socket posts. The board, although not a professional PC board, works very well. Possibly, the main advantage of a wire wrap board in that time, besides lower cost, was its capacity to mount and wire more chips on a board compared to a same sized PC board. This WW board has 77 chip sockets mounted on it. The top of the Viper cabinet and ROM/RAM board was designed so the 4 philip screws, that fasten the Astrocade console top and bottom together, could be removed without dissasembling or disconnecting anything within the Viper cabinet. This feature provides a fairly easy way to gain some access to the top of the Astrocade motherboard or utilize the DIP switches for software development. PIC6 The Astrocade power transformer was removed from its plastic housing to help it run cooler and perhaps extend its life. A 120vac mini receptacle was placed inside the plastic housing, then mounted inside the Viper cabinet. A heat sink, probably not really needed, was placed on top of the XFMR. A white fuse holder, barely visible behind the Archer power XFMR, was wired to the Astrocade XFMR to help protect it from a current fault. The +5V,+12V,-5V power supply was purchased at Radio Shack a long time ago. Today, a triple power supply like this might be hard to find. Look for a +5v,+12v dual power supply or two singles, which are physically small today. Then, tap -5V and a ground wire from the Astrocade motherboard. The horizontally mounted 120vac forced air cooling fan was elevated and directed at the cutout hole in the Viper cabinet top and Astrocade console bottom. PIC7 The 8 dynamic RAM chips and chip U23 were removed from the Astrocade motherboard because they would conflict with the screen RAM on the ROM/RAM board. Their removal also lowers the load placed on the motherboard power supplies. Chips U21 and U22 can be optionally removed because they are not needed. All of the associated decoupling capacitors for these chips and the RAM pull-up resistors were also removed. The +12V regulator is also not needed and may be removed in the future. Presently, there is a 1200 ohm resistor soldered from +12V to ground at a screen RAM chip solder pattern. This resistor quickly discharges the regulator's output capacitor when the power is turned off. The custom data chip has a custom black heat sink on top of it. The 27 ohm, 1W resistor R1 was moved to the left so the 24pin WW socket could be mounted on the bottom of the motherboard. The -5v power supply line, if desired, can be tapped off the motherboard for use with the four 4KB banks of screen RAM. Current draw is only a few mA. A ground wire was also added to the motherboard, for connection to the ROM/RAM board, as an addition to the 2 ground lines using the 50pin expansion. PIC8 A closer view of the low-res screen RAM area reveals the 6 blue wrapping wires connecting the custom address lines MA0-MA5 from the motherboard to the 24pin ribbon cable socket. This photo shows a better view of the -5V tap wire and the +12V discharge resistor. PIC9 This photo shows one end of the relocated 27 ohm, 1W resistor R1 wired to the +10V regulator VR2 input using a pair of twisted wrapping wires. A total 0f 17 wrapping wires were connected from the bottom of the motherboard to the 24pin ribbon cable socket. From left to right, they are: 1. Serial 0, Serial 1, blue 2. DATEN, white 3. MDO-MD7, yellow 4. RAS0-RAS3, red 5. Inverted 7M clock, yellow 6. Inverted System I, white NOTES: The Serial 0 and Serial 1 input pins 11 and 12 on the custom data chip must be disconnected (cut with a sharp hobby knife) from each other and also disconnected from ground. To see MCM Design's motherboard modification procedure: Go to BallyAlley.com. Then, go to the Documentation/Hi-Res Astrocade Upgrade section. Scroll down and select the Hi-Res Package 2. Select "Low/High Resolution Modification Procedure" and read steps 1 thru 15. Reference also "Modified Motherboard Schematic" and its accompanying layout in the Hi-Res Package 1. The MCM Design address listed in Package 2 is no longer applicable. End of tour. MCM Design, Aug 2018