budget cards don't work if voltage=0 ?

[Fox-xxxx]

3 cards, 1 splitter, vlc, linux 2.6.21.1

1 card set voltage=13 result work
2,3 set voltage=0 result don't work

if 1,2,3 cards set voltage=13 result don't work (vlc always restart after
1-3 seconds and says that can't tune)
change 4 differents splitters same result

looks like does not switch on tuner or something else if voltage=0 !
why does vlc always restart if all cards use voltage ?