[robespierre]

There is a second connector on the video card which looks like RGB CGA, is there any way to connect it? Is there any way to verify that the video card is not dead? I can check the CGA pins with an oscilloscope, should be some signals on it? Too many unknowns and I have no second working machine to replace parts one by one and find the failed component :(

The DE9 port on Impact cards is for one thing only, stereo glasses. Earlier generation boards used an industry-standard MiniDIN-3 port for this which caused less confusion.

At least, a single "beep" from the speaker after power on gives hope that the motherboard is booting, but should it display something like BIOS on the screen without any SCSI drive and without an audio module? I think it should, but I never used SGI before.

The machine displays a "Welcome to Indigo2" screen at 1280x1024 resolution. No audio card isn't a problem, although without it there are no boot tunes to use for diagnostics.

For now, I've ordered RS422 to USB adapter, will try to see the boot log via serial, will try when the post will arrive. But I'm not sure yet if it works for Indigo 2.

I successfully used such an adapter with a MiniDIN-8 null modem cable, sold as "ImageWriter II cable". Note that the machine displays its interface on the graphics output when it detects a keyboard, and on the serial port otherwise. So to see output over RS422, the keyboard should be detached.