Free Play ROM Hack Description and Installation:

Download installation instructions Acrobat PDF file: Biltronix_Sega_Star_Trek_Free_Play_Hack_Installation.pdf
Download CPU ROM Images: Star_Trek_CPU_ROM_Images.zip

Description:

Regarding Free Play:

Sega created the Star Trek color vector arcade game machine in 1982.  The game is based on the G80 platform that was also used for some other games such as Eliminator, Tac Scan, Space Fury, and a few more.  Now, so many years later, most of the surviving machines live within privately owned arcade game collections.  For home use machines, the requirement to feed the machine quarters or tokens may at times be a little inconvenient.  Collectors who are purists might not mind this; after all, it is how the machines were original supposed to work.  More casual collectors may appreciate being able to turn on all of their machines and set their guests loose in the arcade without worrying about handing out tokens or having to open the coin doors to add credits.  While there are other ways to add credits such as adding hidden crediting switches or installing an extra wire from a player-start button to a coin switch, it is generally desirable to be able to simply flip an existing option selection switch (called a DIP-switch) on the original electronic game board to select or enable a built-in free play operating mode.  That way, the player can simply press the start button and play.  Many games had such a feature right from the factory but Star Trek sadly did not.

Fortunately, a very talented game collector and enthusiast recently created a ROM hack to allow Star Trek to operate in free play mode.  No, it wasn’t me.  I cannot take credit for this fine contribution to the arcade hobby.  That honor goes to:

Mark Jenison
Vectorlist thread: http://www.vectorlist.org/Vectorlist/2006/04/0039.html
Webpage and patcher tools, game hack links: http://users.rcn.com/jenison/mars/romhacks/
Download zip file: http://users.rcn.com/jenison/mars/romhacks/startrek_freeplay_v1.zip

ROM Hacks:

Put simply, a ROM hack is a relatively simple way to change the functionality of the game by replacing the original program code with modified code by swapping the original EPROM chips with new ones or by erasing the existing chips and reprogramming them. The best option is to program new chips and save your old working ones as a backup.

The game code is typically stored within PROM or EPROM chips, hence the name "ROM hack". The game program code (the data that goes into the chips) is stored on your PC within files called "ROM images". To install any ROM hack, you first need a new EPROM chip that is programmed with the modified ROM image. You have the option of buying preprogrammed chips from an appropriate supplier (ie: HobbyRoms.com, Arcadechips.com), having a friend who has the required equipment program new chips for you, or if you have your own EPROM programmer, you can do it yourself. Once you have the new EPROM chip (or as many chips as required), all you have to do is remove the original chips and plug in the new ones.

 

Installing the Star Trek Free Play Hack (Method #1):

If desired, refer to the links above to get the patcher tools.  The free play hack is presented on Mark's site without the game ROM image (to avoid copyright infringement I would think) and the patcher is a tool that can be used to modify the original ROM image that you must provide or acquire yourself.  I had some problems using the Java patcher (wrong Java version, typical Java issue in my experience) so I just dug into the script and pulled out the information specifying the changes.  If the patcher works for you, that’s great.

To apply the hack my way, do the following:

1. Remove the original 2716 (2k x 8) EPROM chip from location U25 of the CPU board.  The chip should be labelled 1873 or 1873A.
2. Use a universal chip programmer to read the chip and save the image to a file.
3. Edit the appropriate bytes using any free HEX editor program and save the modified copy to a new filename.  Refer to the table below for the addresses to edit and the values to enter.
4. Once the new CPU ROM image is in hand, burn it (flash it, write it, program it, whatever) into a blank 2716 (2k x 8) EPROM chip. 
5. Plug in the newly programmed EPROM chip at location U25 on the CPU board.  Enjoy free play.
   The CPU EPROM image data is modified as follows:

After applying the above CPU ROM hack, your Star Trek machine will run normally but without coins.  Just press either player start button to play.  The attract screens still all work so screen burn is not a concern.

 

A Better Way To Get Free Play (Method #2):

A better application of the hack described above would be one where you could easily switch the game between the original coin play mode and the new free play mode by flipping an internal switch instead of having to swap the CPU EPROM chips.  Fortunately, this is extremely easy to accomplish.

This method requires only a tiny bit more work than the first method.  All you have to do is program a 2732 (4k x 8) EPROM chip and wire its highest order address input to a switch.  Once programmed, the 2732 has the normal code in the bottom half and the free play code in the upper half.  The switch selects which half will run and thus provide either coin play mode or free play mode.  Fortunately, the 8’th DIP switch at SW1 is not used by the original game code so we’ll use this switch to select coin play mode or free play mode.  Closing the switch (on position) selects coin play mode.  Opening the switch (off) selects free play mode.

To make your job simpler, I have provided the original and modified binary image files on my website for you to use to apply this modification. 

Download CPU ROM Images: Star_Trek_CPU_ROM_Images.zip

Filename	Description
cpu1873.bin	The factory original unmodified CPU EPROM image of the chip located at U25 on the CPU board.  It is normally programmed into a 2716 (2kx8) EPROM.  It requires coins to play.
cpu1873f.bin	The completed hacked CPU EPROM image file for free play mode.  This is intended for a 2716 (2kx8) EPROM chip that would be swapped with the original CPU EPROM chip at U25.  This provides free play mode but does not allow an easy switch back to coin play.  You would have to swap the original chip back in again.
cpu1873cpfp_2732.bin	The image file used to program a 2732 chip (4kx8) that will be used to replace the original CPU 2716 EPROM.  It is the concatenation of files cpu1873.bin and cpu1873f.bin.  This version allows switching between coin play and free play. Warning!  Refer to and follow the installation instructions below carefully or you could damage the CPU PCB and/or your machine.  This modification is perfectly safe when installed correctly.

 

Switchable Free Play Modification Installation:

1. Remove the original 2716 (2k x 8) EPROM chip from location U25 of the CPU board.  The chip should be labelled 1873 or 1873A.
2. Get a new or used blank 2732 (4k x 8) EPROM chip.
3. Use a universal chip programmer to burn the new chip with the “cpu1873cpfp_2732.bin” image file.
4. This is where you must be extra careful.  You must plug in the newly programmed 2732 chip at location U25 on the CPU board, however, you must first bend pin 21 outward such that it does not enter the chip socket.  Pin 21 of the chip socket is tied to the system +5V power supply.  If pin 21 goes into the chip socket, the play mode selection switch will short the system +5V supply to ground when it is closed (on).  This would be very bad as it would free the genie from the bottle if you take my meaning.
5. Cut a piece of 30ga solid insulated wire (wire-wrap wire) about 6” long and strip each end to expose about 0.1” of wire.
6. Wrap one end of the wire around the protruding pin 21 of the new 2732 chip and very lightly solder the connection.

Here’s what it should look like at this stage ( Click pics to enlarge ) :

Make sure that pin 21 is not inserted into the socket.

Wrap the bare end of the wire around the pin and solder it to the protruding pin.

 

7. Route the wire towards the pull-up resistor for SW1 (8x resistor package RP1) under existing component bodies as shown in the photos below.
8. Solder the end of the wire to RP1 pin 9.  This is the pull-up resistor that is connected to DIP switch number 8 of the 8-switch package SW1.

 

The complete installation looks like this:

 

To select the desired play mode, coin or free, simply select it using SW1-8. Switch SW1-8 is the last one on the right. It is shown here in free play mode (up = off). Just flip it down for coin play mode.

 

Enjoy Star Trek Free Play !!!

 

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