Thanks to Will Howard for service and user technical manuals.
Pressing ESC during boot enters MFM-200 command line debugger that is contained in ROM. BIOS settings can be changed with SETUP command.
The external power supply is 16.5V (machine will work on lower voltage levels, even 12V) and the ground is in the center of the plug.
Floppy Disk Drive
Hard Disk Drive
My Supersport came without any HDD. I tried installing Compact Flash IDE drive emulator, but it did not work – it caused the display to be malformed. What works fine with this machine is a commonly available SD card IDE drive emulator. No tricks are needed, just connect it as use as an internal hard drive.
Fixing Backlight CCFL on ZenIth SuperSport 286e
Display backlight was broken on my machine. The power supply module located in the laptop base is responsible for producing the voltage for the CCFL lamp in the display. A transformer that was part of that circuit was damaged. CCFL is served by an integrated hybrid circuit called TSHIC-CCFL2. This chip produces waveforms for T301 transformer, which secondary winding is connected directly to the CCFL lamp. TSHIC-CCFL2 circuit is powered by +12V from the power supply and is enabled by +5V signal fed from the motherboard through Q301 transistor. Additionally, the brightness potentiometer in the display base is connected to the circuit for backlight brightness control.
The CCFL circuit can be replaced by a modern universal laptop or monitor inverter board, for example GYT-DK0205.
Original TSHIC-CCFL2 and T301 as well as Q301 can be removed from the power supply board.
The inverter board can be connected to the +12 and GND pins of former TSHIC-CCFL2 and directly to +5V control pin on the motherboard connector. The brightness control can be probably also adjusted to the new board, but I have not tried to do that. Connecting the brightness pin on my inverter board to ground makes it work on highest settings and I see no reason to adjust it.