13 Dec 2017

Sega Master System 2 (repair)

This console was given to me as faulty.
It wasn't doing anything (balck screen, no sound).
I opened it and was greeted by a sticker with hearts on it, someone weird had opened the console before and left a mark.

First thing I did was to check the voltage regulator: 5V, fine.
Then I started to probe signals on the CPU, work RAM, and BIOS ROM: pin 22 (signal /EXTM2 which I consider being equivalent to /CE) was floating on the BIOS ROM.
According to the schematics it's generated by the custom chip IC5 on pin 12 and is also connected to pin 11 of the cartridge connector:

Connection between IC5 and the cartidge port was fine however the one from the cartridge port to the BIOS ROM wasn't. I patched it with a piece of kynar wire :

And tested the in-built game :

And a catridge game :

Console fixed.

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