Power to quad LNB

Ger Roe

I had been operating a twin LNB feeding two tv's - one using a separate set top box and the other with an integrated Sat tuner. All was working well and both TV's could receive the satellite signal independently.

I have now changed to a quad for planned expansion and have an issue where the TV with the integrated tuner, will not receive until the other TV with the set top box is also turned on.

I know it is LNB power related, but does a quad require a different power arrangement to allow the integrated sat receiver TV to operate independently? Would that TV not pass power to it's own LNB port anyway?

I am a bit baffled at the moment, any advice would be appreciated.

Ten Pin

Maybe try different combinations of LNB ports to box and TV?

Try TV on it's own with box feeds disconnected, that won't solve the problem but it'll show if TV is providing any power to LNB.

Does it matter which channels are requested on each device? Is there possibly some issue with polarisation voltage?

Ger Roe

It looks like the TV is not providing power, but I can't see any menu setting on the tv to do so .... and I am sure it worked independently with the twin LNB... although at this stage I am beginning to doubt myself.

Am I right in assuming that there is nothing additional to do for a quad installation, that each LNB port should be powered independently by the connected device?

I am hoping someone might have previous experience of the issue before resorting to going back on the roof to change back to the twin.

dubrov

Quad should be the same. Check the tv settings as there is generally an option to enable/disable power to the lnb

Elvis Hammond

It won't be anything to do with settings. This problem has come up here before, last time resolved with the problem receiver being replaced, although no indication was provided of the actual cause of the fault.

I can only imagine that people are managing to 'blow' something in the LNB power supply when they connect up, that somehow allows it to still function when the other receiver is powered on.

Ger Roe

Eventually solved this... in case it helps someone else, here is the background.

The replacement LNB was a quad with a terrestrial aerial input. When I connected it up the terrestrial signal was not coming through at all and one sat receiver would not receive unless the other one was switched on.

The terrestrial side was using a new antenna, so I was not sure I was even receiving a signal but when I connected the antenna directly to the TV, there it was. So on the face of it, it looked like the LNB was faulty.

I decided to go back to the original twin LNB and in doing so, the connector on the feed cable to the TV that was seemingly not powering the LNB, broke inside its rubber protection boot. It was corroded and by the look of it, the outer core (screen) was not connecting.

It looks like the connection was just hanging in and moving it to do the new install made it fail. It wasn't making good enough connection to take the power from the receiver, but when the other one was switched on, the screen connection was made by that and so it could receive a sat signal on the damaged cable port, but it could not pass the terrestrial signal - looks like only the higher frequency signals were being passed through.

A strip back of the cable and a new connector later and all is well - both sat ports working independently and the terrestrial signal is also coming through.

So ... the problem was a bad screen connection on one of the ports that only allowed a sat signal through when another receiver was powering another port (making the screen connection?), but it would not allow the terrestrial signal through.

Johnboy1951

Does this imply that powering one port of the LNB is sufficient and no others need to be powered to use all four ports>

I remember asking about this some time back and was told each port had to be powered individually ......

Elvis Hammond

Johnboy1951 wrote: »

Does this imply that powering one port of the LNB is sufficient and no others need to be powered to use all four ports ...

No, it just means the dodgy circuit is completed when another receiver with a good connection is powered on.

Johnboy1951

Elvis Hammond wrote: »

No, it just means the dodgy circuit is completed when another receiver with a good connection is powered on.

the problem was a bad screen connection on one of the ports that only allowed a sat signal through when another receiver was powering another port (making the screen connection?), but it would not allow the terrestrial signal through.

I am not quite seeing how a dodgy/broken screen on one can be 'fixed' by sending power through another cable.
The other cable's screen would be permanently connected in any case.

So the only difference is the sending of power through the second cable.

Maybe you could explain what I am missing? Thanks.

Elvis Hammond

I'm kind of missing an explanation myself, as I don't know enough about how the electronics work, but in this case & others that have come up before, it definitely seems as if a faulty 'earth' side of a circuit can be completed when a receiver with good connections is powered up.

Where the fault lies is another matter; in this case the coax cable, but I suppose could also be in the power supply or even the building electric wiring.

Johnboy1951

Elvis Hammond wrote: »

I'm kind of missing an explanation myself, as I don't know enough about how the electronics work, but in this case & others that have come up before, it definitely seems as if a faulty 'earth' side of a circuit can be completed when a receiver with good connections is powered up.

Where the fault lies is another matter; in this case the coax cable, but I suppose could also be in the power supply or even the building electric wiring.

The only explanation I can imagine is that if the coax screen is broken and the LNB port works when another port receives power from a second device, is that the second port's power is used to power the faulty port.

Maybe someone else has an explanation ...

Elvis Hammond

Johnboy1951 wrote: »

... the second port's power is used to power the faulty port.

No, the 'live' side is still intact, & the faulty receiver still powers & controls switching of its LNB port, as long as the other receiver is on.

Johnboy1951

Elvis Hammond wrote: »

No, the 'live' side is still intact, & the faulty receiver still powers & controls switching of its LNB port, as long as the other receiver is on.

Current cannot flow from the device with the faulty connection in the absence of its return path (screen of coax) ...... unless both devices are not of the 'double insulated' type and maybe the Earth connection could provide a return path.

That seems unlikely TBH these days.

Elvis Hammond

Johnboy1951 wrote: »

Current cannot flow from the device with the faulty connection in the absence of its return path (screen of coax) ...... unless both devices are not of the 'double insulated' type and maybe the Earth connection could provide a return path.

That seems unlikely TBH these days.

There's no connection to mains earth. The DC return path for the faulty receiver must be via the 'good' one & the other mains wiring, but only when the other receiver is powered on, for whatever reason.

Johnboy1951

Elvis Hammond wrote: »

There's no connection to mains earth. The DC return path for the faulty receiver must be via the 'good' one & the other mains wiring, but only when the other receiver is powered on, for whatever reason.

Through which line of the mains wiring?

If not earth, then either of the other two would indicate that the coax is connected to either mains live or neutral ......... a definite 'no no'!

.

Ger Roe

If it makes any sense to the discussion... the satellite signal on the bad connection port (feeding TV) was not as strong as on the other port (feeding STB) - showing as 50% less on the onscreen level meter. I initially thought this might have been a LNB skew problem and was not overly concerned.

The set top box in one room and the sat tuner integrated tv in the other, are both powered on the house wired mains sockets.

There was a similar discussion here a few weeks ago with someone else having an issue where switching off one receiver resulted in signal loss on another. I don't think it was solved, the bad connection to the shield in my case is certainly a factor, any thoughts on why the terrestrial signal wasn't passed through? I can only think that it must be frequency related?

Johnboy1951

Ger Roe wrote: »

If it makes any sense to the discussion... the satellite signal on the bad connection port (feeding TV) was not as strong as on the other port (feeding STB) - showing as 50% less on the onscreen level meter. I initially thought this might have been a LNB skew problem and was not overly concerned.

The set top box in one room and the sat tuner integrated tv in the other, are both powered on the house wired mains sockets.

Are they both three wire mains cables or the more common two wire cable for consumer devices?

There was a similar discussion here a few weeks ago with someone else having an issue where switching off one receiver resulted in signal loss on another. I don't think it was solved, the bad connection to the shield in my case is certainly a factor, any thoughts on why the terrestrial signal wasn't passed through? I can only think that it must be frequency related?

Ger Roe

Johnboy1951 wrote: »

Are they both three wire mains cables or the more common two wire cable for consumer devices?

Both the TV and the STB are two wire - plastic earth pin on the plug.

Johnboy1951

Ger Roe wrote: »

Both the TV and the STB are two wire - plastic earth pin on the plug.

That eliminates the mains earth wiring from the equation, and as the coax should not be connected to either live or neutral, it effectively eliminates the whole of the mains wiring.

Is it not more likely that power is applied to the problem port from the powered port, either by design or 'leakage'?

Ger Roe

Johnboy1951 wrote: »

That eliminates the mains earth wiring from the equation, and as the coax should not be connected to either live or neutral, it effectively eliminates the whole of the mains wiring.

Is it not more likely that power is applied to the problem port from the powered port, either by design or 'leakage'?

That's what I thought when I realised that the lower signal level was not Skew related and it was resolved when the screen connection was properly restored. I think the signal frequency issue of the terrestrial not coming through might be a factor in working out how the 'leakage' might be coming through. Some path that only higher frequencies can pass?