tikimune Wrote:... now I know that 22khz is not only used for vertical but also for some horizontal channels.
i definitely get better understanding of your setup. let me explain how the (Universal) LNB is controlled:
* 13V (or a little over) supplied by the receiver means "Vertical"
* 18V (or a little over) supplied by the receiver means "Horizontal"
* 22 kHz off (22 kHz are not sent by the receiver) means LNB Local Oscillator Frequency (LOF) is set to 9750 MHz
* 22 kHz on (22kHz are sent by the receiver) means LNB Local Oscillator Frequency (LOF) is set to 10600 MHz
so, based on the above on you problem description it seems your quad LNB starts to ignore power supply for "Vertical" sends by your 6920 card, when the other receivers are in use. i think it couldn't be hardware fault of your 6920 card, because otherwise you won't have vertical at all (if the LNB power circuit is broken) under any circumstances. so, it really sounds like incompatibility problem between the LNB and the 6920. in any case as i mentioned there is no problem to replace your 6920 board, but i believe the same will happen, because it's for some reason your quad LNB doesn't like the power supply for "Vertical" that is sent by 6920 when the other receivers are in use. i agree it's really strange, because at least i expect the quad LNB has 4 completely independent LNBs inside, which doesn't seem to be true with your quad LNB. actually, maybe, your quad LNB manufacturer will have better idea about the problem, because they know how their LNB is working internally.