After trying to use the EN50494 feature of neutrino-mp, I found that as soon as I attached the coolstream neo to my coax-”bus”, all other receivers on the same bus could no longer tune any frequency. After quite some investigation, I found out, that the tuner does not lower the voltage to 13V if there is less than about 10mA of current load on the “LNB in” coax output.
I tried to work around the problem in software. However, that did not work too well, because if the neo was the only active receiver on the bus, then the SCR matrix would shut down if there was no voltage applied. So I checked if there is a way to simply fix the broken hardware.
There is. Next to the tuner “tin box” there is a transistor that has the 14/19V at one of its terminals. Just adding a 1.1kOhm resistor from there to ground made the voltage switch correctly even without any coax cable attached.
The picture is not very good but it shows where the LNB power can be tapped.
Note: use this at your own risk, soldering the resistor to the wrong terminal or shortening the wrong solder points might very well kill your box. You have been warned.
It is also very well possible that better soldering points exist, however this solution can be implemented without disassembling the box completely by just soldering on the top side of the PCB.
It would be interesting if this modification also solves the huge amount of DiSEqC switching problems that were reported last spring after some software update, it surely solved my EN50494 (aka unicable) bus blocking problem. After all the vendor has issued no statement until today, even though this clearly looks like broken (by design) hardware…