Amstrad PC - PC3086 Motherboard Option Links

PC3086 Option links

The PC3086 motherboard has option links all over it. They are used mainly to disable builtin motherboard functions.

LK1: Drive A: Changeline
Put a jumper on this link if drive A: does not have a changeline.
LK2: Drive B: Changeline
Put a jumper on this link if drive B: does not have a changeline.
LK3: Disable power-on self test
Put a jumper on this link to skip the power-on self test.
LK4: Memory size
According to the manual, this should be left with the jumper on pins 2 and 3. The service manual implies that moving it to pins 1 and 2 reduces the memory to 512k, as on earlier XTs.
LK5: BIOS ROM size
According to the manual, this should be left disconnected. The service manual schematic suggests that, as on the PC1512, it controls BIOS ROM size. If it is connected, the ROM is treated as 32k (2x16k) rather than 16k (2x8k).
LK6: Write Precompensation
According to the manual, this should be left on pins 1 and 2 (250ns) rather than pins 2 and 3 (125ns).
LK7: Disable motherboard COM1
Put a jumper on this link to disable the motherboard COM1 port.
LK8: Disable motherboard VGA
Put a jumper on this link to disable the motherboard graphics support.
LK901, LK902: Primary display type
Both links disconnected: VGA (built-in or external).
Both links connected: MDAor