The MGA-1200 saves the settings and uses the DS1216B DIP-28 chip as a clock.
This means as soon the batteries in the chip drain too much it looses the settings.
When the battery’s die, it will give ‘SR’ errors on the screen.
We can repair this by finding a DS1216B or make a more permanent fix. Because the DS1216B are not produced anymore. So it will be trivial when they all run out of battery.
The website minuszerodegrees has a nice manual and research on howto fix the chip and provide it with new battery’s.
On difference is that they only need the clock to get battery power. And we want to supply the NV-RAM chip also power. So i opt to restore both batteries in the DS1216B.
Minuszerodegrees has a nice howto, to disconnect the batteries internally.
I made my own schematic for how i connected them:
I ordered these battery holders for CR2032 cells, but you can use any.
I also recycled some old motherboards on a little pcb to create this:
Finally build into the MGA-1200:
After you do this the system is completely reset to stock.
I advice the next settings:
- Cf1: Prt 1
- Cf2: Apr 1
- Cf4: Opt 1 through 4: ON –> Opt 5 through 8 OFF
- Cf5: L0 (english)
- Cf6: Ser 0
- Cf7: Rpo 1
Refer to the service manual to see what settings are set. And howto set them.