Genesis Reproduction Board Guide

Here’s a quick guide on how to populate my custom designed Genesis/Mega Drive reproduction PCBs. There will be more information in the upcoming guides, but this is a good place to check for a good overview of the board. All the through-hole components are on the front side of the board, and all of the surface mount components are on the back of the board. A new design is coming that has through-hole slots for passive components, but not the ICs.

Front Side

IMG_20200605_115527

EPROM

Needed for: Every game
Part Number: 27C322 or 27C160 (remember to kick out pin 32 on the 27C160 if using it)
Function: Holds the ROM file

C1 – Electrolytic Capacitor

Needed for: Every game
Value: ~22 uF, at least 10 V rated
Function: Smooths out supply voltage for the board due to transients on the power supply, prevents quick changes in supply voltage when power is turned off

SRAM

Needed for: Games that save
Part Number: 62256 series SRAM (be sure to get low standby current model)
Function: Holds save game data

Battery

Needed for: Games that save
Part Number: C2032 (socket is designed for yellow ones with pre-attached legs)
Function: Keeps the SRAM on to retain data while power is off

Back Side

IMG_20200605_115537

Solder Pads

If your game does not save: Bridge the solder pad in the middle of the 74HC139D package (to the left of “IC3” marking)
If your game saves: Bridge the solder pad in the right hand corner

C4 – Ceramic Capacitor

Needed for: Every game
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the EPROM

C2, C3, C4 – Ceramic Capacitors

Needed for: Games that save
Value: ~0.1 uF, at least 10 V rated
Function: 
Filters out high-frequency noise that can interrupt the SRAM, Flip-Flop, and Decoder

R1, RC, RB – Resistors

Needed for: Games that save
Value: ~1 kΩ for R1 and RC, ~10 kΩ for RB
Function: Part of the battery management and saving logic circuit

D1, D2 – Diodes

Needed for: Games that save
Part Number: Any small signal diode will do, I used 1N5819
Function: Combines battery and main power supply to power the SRAM

Q1 – NPN Transistor

Needed for: Games that save
Part Number: 2N2222 or equivalent
Function: Part of the battery management and saving logic circuit

IC2 – D-type Flip-Flop

Needed for: Games that save, for ROM files that are larger than 16 Mbit
Part Number: 74HC74 or equivalent
Function: Part of the saving logic circuit

IC3 – Decoder

Needed for: Games that save
Part Number: 74HC139 or equivalent
Function: Switches between activating the ROM or the RAM during gameplay

Important Rework!

Needed for: Games that save, that have ROM files 16 Mbit or smaller
Rework: Solder pins 2 and 3 together on the 74HC139. Make sure the 74HC74 is not installed on the board.

IMG_20200922_222528

Examples of Completed Boards

If your game doesn’t save, it’s very easy to finish. You only need the electrolytic capacitor, one ceramic capacitor, and the EPROM.

If your game uses save data, you’ll need to populate every component, as shown here.

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