20 Feb 2019

System 16B motherboard - Sega (repair log)

The third and last board I got from ekorz. It was sent as non going but I found game logic was actually working but:
- sound was totally absent
- colours were wrong (mostly yellow screen)
- text and background layers were missing

It's hard to see but sprites are actually drawn in white.
By looking at the board something caught my eyes: UMC (United Microelectronics Corporation) branded RAM chips (known to be unreliable).
I probed them:
- 1 * 6116 type for sound RAM: was bad
- 2 * 6116 type for palette RAM: one was bad
- 2 * 6116 type for text RAM: both were bad

Once replaced:

Motherboard fixed.

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