I have found an old Z80 computer which was used in production in the 80’s. Specs seems to be a video card (or let’s say, a text card with video output), a Z80 MCU, 5,25″ floppy disk drive and a keyboard interface.
Connected to power, keyboard and TV the machine shows the usual monitor program. I used a good old PC AT keyboard, which seems to get power from the PC as I can see the power on self test of the keyboard (blinking keyboard LEDs). However, keyboard does not seem to work, no keystroke is displayed.
As you can see in the picture, the mainboard contains the Z80 MCU, the floppy disk controller chip D765AC, Mostek 8410 DMA controller, ROM (red label) and RAM chips. Keyboard is connected to the front panel using the small grey ribbon cable. The wide ribbon cable on the top is connected to the floppy disk.
Now the big question, why does the keyboard not work? Since it gets power from the connector I assume that it is the right keyboard type (PC AT). The keyboard works on other computers, so maybe the Z80 board is broken? Or are there older protocol variants?