DM800 DiseqC switch inline amp

[davvo]

DM800 4 way DiseqC switch 28/19/16/13 east
all switch ok all SD work fine
but about 5 HD channels glitch on 28 east

so i put in a 20db inline amp HD channels now fine no glitch
all channels on 28/19/16/ fine

now i get no signal on most of 13 east SD and HD

so i take amp off
all channels on all sats fine apart from the 5 HD channels that glitch on 28 east

and with inline amp signal on all sats goes lower not higher

amp is on the right way

any help appreciated