PC5086 option links
The PC5086 manual describes two option links on the motherboard:
LK1: Enable VGA
This link usually has a jumper fitted. If the jumper is disconnected then the built-in VGA is disabled and a display card must be fitted to the expansion bus.
LK7: Enable hard drive
This link enables the built-in IDE controller. If the PC does not have a hard drive fitted, then the jumper must not be fitted.
The following links are briefly mentioned in the service manual. Any deductions from their settings are my own.
LK2: Drive type
A jumper on this link connects pin 13 of the floppy drive connector to the Drive Type input on the peripheral controller. This would only be used by dual-speed 5.25" floppy drives.
A jumper on this link connects pin 13 of the floppy drive connector to the 'alternate write precompensation' pin on the peripheral controller.
LK4: Hard drive reset control
According to the service manual, this should be on pins 1 & 2 if the hard drive is a Seagate drive, 2 & 3 for other drives, and disconnected if there is no hard drive.
LK14: Speaker volume
Connect pins 1 and 2 for loud, 2 and 3 for quiet, and leave the jumper off to use the normal volume control wheel.