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Title            : Sega Coin Hack                                           :
Date             : 17-November-1997                                         :
Author           : Paul Tonizzo                                             :
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+----------.
 Background \ 
+------------`--------------------------------------------------------------.
                                                                            :
The 3VAC om Sega G80 boards is only required to keep the Z-80 from          :
reseting. The whole idea Sega had behind this was that they found a quick   :
power on/off would sometimes credit the game. The 3VAC guaranteed a reset   :
CPU on powerdown/up.                                                        :
                                                                            :
The really annoying thing is that the coining circuit requires a 1ms pulse  :
to actually coin the game. This was another of Sega's ideas to reduce the   :
chances of someone tripping a free credit any other way than with a coin.   :
                                                                            :
Here's a simple 555 timer circuit that will let you use a regular           :
Jamma-type low signal to coin the game (you can also use the service        :
switch but this doesn't help for 4-player Eliminator), to defeat the        :
idiotic coining mechanism on Sega's G-80 games.                             :
                                                                            :
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+----------.
 Disclaimer \ 
+------------`--------------------------------------------------------------.
                                                                            :
Read these instructions fully before starting!!! Do not attempt this        :
procedure unless you are comfortable with using a soldering iron and this   :
type of work.  You should also be taking anti-static precautions when       :
handling any of the components including the board. Lastly, I cannot be     :
held responsible if your board blows up so proceed at your own risk!        :
                                                                            :
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+---------.
 Materials \ 
+-----------`---------------------------------------------------------------.
                                                                            :
	Qty	Description                                                 :
	---	-----------                                                 :
	1	555 timer chip (8-pin)                                      :
	1	8-pin socket (for the 555)                                  :
	2	0.1 uF capacitor (use mylar caps)                           :
	2	1 Meg ohm resistor                                          :
	4	1N4001 diodes (4-player Eliminator only)                    :
                                                                            :
	You should be able to use a really small piece of perfboard to      :
	make this. (1-1/2" square would do it.)                             :
                                                                            :
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+---------.
 Procedure \ 
+-----------`---------------------------------------------------------------.
                                                                            :
The basics are that the circuit uses a 555 timer to generate a clock pulse. :
The pulse itself is low for ~1ms and then high for ~1ms and repeats itself  :
(1ms was the optimal value for the pulse width to get the coin to trigger). :
The circuit itself is not at all unlike the rapid fire circuit for some     :
Midway games (but it has been greatly simplified).                          :
                                                                            :
Wire it up as follows:                                                      :
    - pins 4 and 8 of socket to +5v                                         :
    - one side of first 1M resistor to +5v, other side to pin 7 of socket   :
    - one side of second 1M resistor to pin 7 of socket, other side to      :
      pins 2 and 6 of socket                                                :
    - one side of first 0.1 uF cap to pin 5 of socket, other side to pin 1  :
      of socket                                                             :
    - one side of second 0.1 uF cap to pin 2 of socket, other side to pin 1 :
      of socket                                                             :
    - pin 1 of socket to pin 5 on G-80 CPU board                            :
    - pin 3 of socket to pin 6 on G-80 CPU board                            :
                                                                            :
For all games except 4-player Eliminator:                                   :
    - pin 1 of socket goes to coin or a coining button of some kind         :
                                                                            :
For 4-player Eliminator:                                                    :
    - you also require 4 general purpose diodes (1N4001 will do)            :
    - take all 4 diodes and the ends closest to the black line should all   :
      be tied together (this is the end the electrons CAN flow to). These   :
      ends then get attached to pin 1 of the socket                         :
    - the other ends of the four diodes should go to the coining buttons    :
      (one for each player)                                                 :
    - the coining buttons also go to pins 2-5 on the i/o board.             :
    - the only other thing that changes on the i/o board is that the board  :
      outputs that go to pins 5 and 6 on the G-80 CPU board should be cut.  :
                                                                            :
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