If you can hook up the Vector's "tape in" to your soundcard "line out", try opening this web page:
http://sensi.org/scalar/ware/555/

then click on the ellipsis next to "test.zip" - you'll see

testtp [pack].rom 997▶
testtp.rom 1024▶

Power up the Vector, then press and release "VVOD" and "BLK" simultaneously to make sure a proper hard reset and entering the bootloader mode.

Then click on the Play button symbol next to "testtp.rom"
When the sound stops playing, the "rus" led should start flashing.

If that's the case, press and release "BLK+SBR" simultaneously - this will deactivate the bootloader and start executing the manufacturer self-test.