Is it 17v or 18v?

[Captain Jack]

I seem to have an issue with my polarity switching on my main Ku LNB (Inverto something-or-other). Verticals are fine but horizonals are black.

The cable run is quite long at around 40m, plus there's a DiSEqC switch at the end of it to flip between C and Ku LNBs. The voltage at the LNB end, when H is selected, is around 17.6V. Is that enough to switch the LNB to the horizontal frequency? The C band LNB seems fine in both polarities. The switch itself causes a 0.4v drop - it's dead-on 18v before that.

Suspected a knackered LNB, I replaced with another Inverto (found in the garage) but that has the same issue. I need to spend some time at the dish end with a meter to see whether the LNB will switch to H at all - just in case the replacement one is also knackered. Also need to try bypassing the switch.

But it's annoying - something I thought was an easy fix is turning into a time sink.

Incidentally - what's a decent C120 LNB these days? There don't seem to be many around...

 

[ozumo]

Specs for current Inverto LNBs state 16V to 20V is needed to switch to horizontal so it sounds like yours are past their past.

 

[Beli1910]

I think that both of your LNBs are defective. I will post one satellite report and look at the voltages for H polarization.

 

[scopus]

Possibly a faulty port on the Diseqc switch? You could reverse Ku abd C and see if the problem then lies with the C Band.
Not seen any new C120 LNB's for a while, usually a convert it job nowadays..

 

[Captain Jack]

Possibly a faulty port on the Diseqc switch? You could reverse Ku abd C and see if the problem then lies with the C Band.
Not seen any new C120 LNB's for a while, usually a convert it job nowadays..

I replaced the DiSEqC switch as well as the cable (well, swapped them over) but no difference. So it just leaves the LNB.

I have a couple of Black Ultra -> C120 flange adapters courtesy of @Trust so may try those.

 

[scopus]

I replaced the DiSEqC switch as well as the cable (well, swapped them over) but no difference. So it just leaves the LNB.

I have a couple of Black Ultra -> C120 flange adapters courtesy of @Trust so may try those.

Ahh OK..I take it you've tried another receiver as well?

 

[Captain Jack]

Ahh OK..I take it you've tried another receiver as well?

Yeah, tried the F15 as well as the TM5402 MK4.

Incidentally, I also tried the "extra power" option in the E2 option, which raises the voltage by 0.5v but no go.

The receiver works fine on the other tuner input for the T90 with a 10/1 switch in between.

 

[yang sat]

V polarizing voltage range 11-14.5V
H polarizing voltage range 15.5-22V

 

[Satfaca]

Possibly a faulty port on the Diseqc switch? You could reverse Ku abd C and see if the problem then lies with the C Band.
Not seen any new C120 LNB's for a while, usually a convert it job nowadays..

Here some brand new C120 LNBs available:
Inverto Single
Inverto Twin
Invacom Single

As per Captain Jack's issue there is a problem with insuffiecient voltage coming through a long line cable sometimes, specially in moist atmosphere. There are certain (or most) images with "Increased voltage" tuner settings option which can help resolve the problem.

 

[scopus]

Here some brand new C120 LNBs available:
Inverto Single
Inverto Twin
Invacom Single

As per Captain Jack's issue there is a problem with insuffiecient voltage coming through a long line cable sometimes, specially in moist atmosphere. There are certain (or most) images with "Increased voltage" tuner settings option which can help resolve the problem.

View attachment 149631

He tried the voltage increase on his E2 image as per his post, and it didn't work. I have a similar length of cable run here and have never had a switching problem.
Those LNBs have been around a while, you will be lucky to get an Invacom these days, most that are on sale are old stock.

 

[Captain Jack]

I just replaced the LNB yet again with the last remaining C120 one I had (twin Inverto) - it looks very much worse for wear but seems to be working on both polarities (for now).

Looks like I need to stock up on these old stocks.