MegaCD-Connect-BD-Remake

This is the Schematics, PCB and Logic for the Mega-CD Connect BD Targeting the 315-5477 (MCE V1) MegaCD.

It is to replace the 837-8327-01 IC BD MEGA-CD CONNECT BD with a failed ASIC to the older Logic version of the board that has the Peel IC.

The board is not a clone, rather a remake as i do not have access to an original logic board version to do an exact replica of traces.

• The Gerbers have been created using the recommendations from JLCPCB.

• This board uses a GAL22V10 to achieve the same logic functions as the Peel IC. Jed file is provided. Use a MiniPro to write the Jed file to the GAL Chip.

Notes:-

• I have used an ATF22V10B-15PC as a replacement for the GAL22V10. The ATF Works, but i also see this is obsolete. There is ATF22V10C range of chips, but stock seems to be low on these.

• TESTED V2.0 and this worked, but now made V2.2 and is UNTESTED

• Finally got some GAL20v8 Chips, and they do not work. Think this is a timing issue. So please use the GAL22v10's instead, unless someone wants to take a stab at getting the GAL20v8's to work. (Looks at Steve)

Version 2.2 Changes:-

• Moved traces around the middle screw holes, just incase screw heads sub against the silkscreen removing it and causing a short against the 5v rail.

• Moved the IC1 Silk name slightly up.

Version 2.1 Changes:-

• Moved /TRDIR from PIN 23 to PIN 15, This should make it compatible with the GAL20V8

• Added GAL20V8 Logic, but does not work.

• Updated Labels for Tree House Connection, TH1 and TH2

Compiling The Logic

The software i used to make the Jed file was GALasm. It can be downloaded from here https://github.com/daveho/GALasm

Only source files is provide, so you will need to compile GALasm first. I used MacOS to do this, Linux should work and maybe Windows ???

Once GALasm is compiled, use the following command to compile the Logic into a Jed file from within the GAL22V10 folder.

galasm ./GAL22V10.pld

Fitting the Board

1. Post

There is a slight modification required to make the PCB fit in the original housing.

This Post would need a little snip to allow the GAL chip pins to sit correctly in the housing.

2. Tree House J3

If you use a Pin Header, you will need to bend it slighly inwards otherwise it will not fit inside the MegaCD.

BOM

Interactive BOM

Thanks

With thanks to @fabiodl for decoding the logic of the Peel IC

• https://github.com/fabiodl/peelDecoder

Other Resources

• https://circuit-board.de/forum/index.php/Thread/25582-SEGA-MEGA-CD-1-Reparatur-PEEL-18CV8-PLD-auslesen/

• https://www.eevblog.com/forum/projects/help-with-reverse-engineering-unexpected-behavior-of-peel18cv8-223204/

!!!!! WARNING !!!!!

Use at your own risk. I accept no responsibility.