12 Jan 2017

Sega Mega CD I (JAP) - Sega (repair)

Today's patient: a Japanese Mega CD model 1, a beautiful machine, but having a video bug on the Sega logo which is supposed to rotate on the attract screen. Also the machine hangs 1/2 or 1s after entering the CD menu: 


There are 2 possible causes:
- one or both word RAMs are dead
- one or several traces are broken

One of the most famous disease of the Mega CD 1 being the capacitors leaking with age and spreading their nasty fluid all over the board eating traces and vias, I will start to probe each trace between the RAMs and the associated Sega custom chip.

Opening the beast:


I had to remove the small daughterboard soldered to the main board (a last minute fix by Sega to correct a design flaw, that's why this board is absent from the newer revision motherboards) in order to have access to the Sega custom chip sitting underneath:


I found a broken trace on IC11 (data line D0). Capacitor C23 has leaked and eaten a trace. I patched it with a piece of kynar wire (the red one, green ones being factory soldered). I soldered one end to the RAM and the other end on a via after testing it was good (impossible to solder directly to the Sega custom chip due to the ultra fine pitch):


Reassembling and test:


Success! 



As I don't want to waste my work I'll do a recap of the board.

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