Copyright 2014,2015 Brian Brzezicki, all rights reserved. Feel free to link to this or use the information within, but please give credit where credit is due.

7/7/2014 - Write up version 1.0
7/8/2014 - Write up version 1.01
7/9/2014 - Write up version 1.03
8/30/2014 - Instructions were wrong, in terms of socket labels
12/30/2014 - fixed typo on address range for 7V, thanks to klov user channelmanic for pointing out the error
7/26/2015 - added plug and play replacement

This is a write up of a hack to replace the galaxian daughterboard with a single 2716 and a single 2764. This hack does not actually permanently modify the board in any way.

Disclaimers

The following hacks are described

What you will need for this hack
  • 1 2716 EPROM chip (or original chip on daughterboard in position Z)
  • 1 2764 EPROM chip
  • about 6 inches of high gauge (thin) jumper wire
  • About 10 inches of electrical tape (optional)
  • 3 28 pin (.6") IC sockets
  • a few inches of insulated thin (28gauge or so) jumper wire
  • A EPROM programmer (or someone to program your 2716 2764 EPROM)
The image below shows the pinouts and the numbering of the 2764 chip (and socket). In the instructions below we will refer to the pin number shown in the diagram
  • Get 3 empty 28 pin (.600) sockets.
  • Take the 1st 28 pin socket, solder together (use some jumper wires) the top 3 pins on the right side (pin 26,27, 28)
  • Cut off the as much of the top right 2 pins (27,28) as possible
  • Grab the 1st 28 pin socket
  • using a very small piece of insulted jumper wire, strip an edge and wrap/solder on pin #14 of the 24 pin socket WITHOUT bending the pin out.
  • bend OUT pin 20 on the 1st socket so it's at a right angle
  • Strip the other end of the jumper wire that you just used.
  • solder the other jumper wire unto the bent leg of ping #20
  • Put aside that first socket for now
  • Grab the 2nd 28 pin socket
  • Pull out the pin for pin #20
  • Put aside that first socket for now
  • Bend out pin #2 on the 3rd 28 pin socket.
  • Solder an insulted jumper wire from pin #2 to pin #20 (strip the ends obviously before soldering)
  • Now stack all 3 28 pin sockets on top of each other
  • Socket 1 at the top
  • Socket 2 in the middle
  • Socket 3 on the bottom
  • Burn your 2716 EPROM with the image for location 7Z from whatever galaxian version you have.
  • Insert this ROM into socket slot 7L on the galaxian board. In can be inserted directly with NO modifications.
    OR
  • If you have the daughter board, you can simply insert the ROM in position "Z" into slot 7L instead.
  • Burn your 2764 EPROM with the following ROMs in the order listed
    • 7U - (ROM address range 0x0000 - 0x07FF)
    • 7W - (ROM address range 0x0800 - 0x0FFF)
    • 7V - (ROM address range 0x1000 - 0x17FF)
    • 7Y - (ROM address range 0x1800 - 0x1FFF)
    Note:
    • ROMs 7W and 7V appear flipped in terms of their actual location in the game program, this is done because address bits 11 and 12 are flipped in our wiring.
    • Here is a image of the neccesary file for Galaxian Midway set 1 to burn onto your 2764.
  • Wrap the socket sides once or twice with a piece of electrical tape to protect the jumper wire and add a bit of stability.
  • Now insert the 2764 EPROM into the top of the socket stack, and insert the whole stack into position 7F. Ensure that the back of the 28 pin socket lines up with the back of the 24 pin socket on the PCB board, obviously the 28 pin socket is bigger than the 24 pin socket is is beign plugged into, so the front 2 pins on each side of the 28 pin socket WILL OVERHANG the 24 pin socket.
  • The original galaxian daughterboard had zip ties holding it down, might as well use the zip tie holes to put in zip ties to hold our socket stack tight!
Done!
7/26/2015 - a plug and play replacement! available for sale at etsy.com $20 plus shipping.

Notes:
24U kit
strapped for 2732
Cut pin #2, isolate from GND
old CS (18) -> pin #2

cut CS trace CS (#18 on 2732) to 27512
wire CS on 27512 (#20 on 27512 to ground