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Testing an LNB

Topper

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#1
Ok just curious to know how to test an LNB using a multimeter from the receiver end. What am I testing? and what results should I get?

Yes sadly I was watching BBC World and suddenly the picture kept disappearing and the no or bad signal message would flash on the screen, I switched off and back on but no signal being received at all. The dish has not moved at all so it is either the LNB or receiver.
 

2cvbloke

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#2
Topper said:
Ok just curious to know how to test an LNB using a multimeter from the receiver end. What am I testing? and what results should I get?

Yes sadly I was watching BBC World and suddenly the picture kept disappearing and the no or bad signal message would flash on the screen, I switched off and back on but no signal being received at all. The dish has not moved at all so it is either the LNB or receiver.
I don't know if a multimeter can do anything with an LNB, I think the best way to see what's died is the substitution method, and of course there could be a leak in the cable causing water ingress, or , there's bl**dy thick clouds up in the sky blocking your signals... :D
 

BadWithComputer

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#3
a multimeter would only test continuity, and i dont think there is any way to test a LNB, except for opening it and checking the internal circuitry :.)
 

dig deep

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#4
Borrow, steal or buy a new one and test it:)
 

member91040

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#5
Test On 0 Amps.
 

Llew

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#6
Careful now - don't use the ammeter check across a live LNB. You'll kill the supply.

Only works in series with the output terminal, but will only tell you if the LNB is drawing current.

Llew
 
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#7
my dear friend .

The LNB can be tested using the multimeter.
U can remove the LNB and keep the negative probe in the centre and the positive probe of the multi meter on the outer dia of the connector of the LNB .Keep the multi meter in the buzzer range and now u can seen some impedence i.e the resistance of about 500-550 ohms.If it is shorted it will be buzzing ,if no continuety there is some disconnection ,if it is showing some impedence of 500 ohms .the LNB is fine.
 

Llew

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#8
Doesn't prove the LNB is fine at all.

Oscillator may be faulty, signal stages may have gone down...
 

member91040

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#9
Are you talking about crystal Oscillator, Can be able to test manually or separately.
 

Llew

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#10
They don't use crystals member91040. They aren't precise enough at GHz frequencies.

They use a FET in conjunction with a dielectric resonator.

Don't ask me how you test it though (although the FET could be).

Llew
 

Topper

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#11
Llew said:
They don't use crystals member91040. They aren't precise enough at GHz frequencies.

They use a FET in conjunction with a dielectric resonator.

Don't ask me how you test it though (although the FET could be).

Llew
I vaguely remember it being called a mosfet? or am I dreaming
 

Llew

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#12
Mosfets, igfets, jugfets: all variations on the theme of field effect transistors. Just different electrical characteristics or structure.

Llew
 

Topper

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IDD CI24 ECONO MM Penta 1.20 Galaxy II
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My Location
Blackburn, Lancashire
#13
I splashed out for a new lnb yesterday, Triax TSI 003. After physically checking the cable and testing the cable with the meter for shorts etc, I fitted the lnb today and whilst not having tuned it properly yet I am receiving Hotbird extremely well so that will do for now.

Strangely enought before I fitted the lnb I powered up the stb with the old lnb which had not been on for a few days and for about 5 seconds it worked then no signal again, more junk for the bin.
 

Channel Hopper

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#14
LNBs by there very nature (sealed, mass produced and cheap) are disposable items.
Nobody checks first, except by substitution, and by then the call out charge, ladder up the wall, connector and amalgamating tape, have already come to many times the cost of the component.

Its also true to say that an LNB of even three years in the field, will usually have issues at some frequencies, even though it appears well, a similar new unit won't have suffered the same temperature / humidity /radiation exposure.
 
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#15
hello all,
newbee on the forum but also in regards to this stuff. Don't hesitate to make fun of me but don't chastise me either ( I could be helpful in something else, who knows?)

As the topic title says, I have suddenly complete loss of signal. I have checked wiring, obstruction, orientation (dish is solidly in place). It happened to both receivers at the same time thus signaling a central issue(?). Did the switch test on screen as well.
sat # 110,118, 119 all "ok", reception verified, switch : DPP33 w/ separator ( all this is greek to me)

so by surfing, I'm now wondering if the lnb is bad and don't know how to test it with voltmeter??

Can you guys guide me? :-worship
Remember, it will be VERY easy to loose me if you start using abbreviations for everything. I do not know what I'm talking about:-ohcrap

Greetings from Oregon
 

Llew

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#16
alainmax said:
hello all,
newbee on the forum but also in regards to this stuff. Don't hesitate to make fun of me but don't chastise me either ( I could be helpful in something else, who knows?)

As the topic title says, I have suddenly complete loss of signal. I have checked wiring, obstruction, orientation (dish is solidly in place). It happened to both receivers at the same time thus signaling a central issue(?). Did the switch test on screen as well.
sat # 110,118, 119 all "ok", reception verified, switch : DPP33 w/ separator ( all this is greek to me)

so by surfing, I'm now wondering if the lnb is bad and don't know how to test it with voltmeter??

Can you guys guide me? :-worship
Remember, it will be VERY easy to loose me if you start using abbreviations for everything. I do not know what I'm talking about:-ohcrap

Greetings from Oregon
Hi alainmax, welcome to the forum.

Forget testing with a voltmeter/multimeter. The only test you could do in theory is to check for the LNB's current consumption, which would involve using the ammeter range of a multimeter in series with the power feed to the LNB. This won't tell you whether the LNB's circuitry is working normally though.

Best to check by replacement, they're cheap enough these days.
 
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#17
Thanks Llew,

gotcha. But the weirdest thing happenend, after 24h of this, it suddenly kicked in again!!!!dunno what's going on but happy again...
Is this bound to happen again? would that be a symptom of a dying lnb?
 

Channel Hopper

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#18
Could be a symptom of any number of things, and it's best to eliminate those first before splashing out on a new one.

Over here the number of domestic Sky boxes that show no signal due to a faulty tuner/power supply should make a quick substitution with a neighbours receiver your first port of call.

Then check the cable for any cuts or damage (is it under the floorboards/house ?).
On the dish itself, spiders can make nests in the front end of central fed LNBs if they can get in, and in the fall squirrels stick food in the front end of C band stuff. I've even seen bushes grow from the dish where a seed has germinated.
 

ralphmagno

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#19
thello to all,
an lnb can only be checked for shorts with a multimeter.
there are some problems that i have seen.
cold solder joint on the mother board where the cable is connected.soldered the joint and it was fixed.
lo 2 broke lo 1 was fine. then the 22 khz was on the signal went dead.
first if amp transistor was shorted causing the level was low.
it still worked but signal and quality was bad.on an AFN decoder the strenth was 45 quality was 0 it was braking up.
changed to a new lnb quality was 8 strenth 65.
plastic lense is open and bugs built nest inside or lense was cracked and was green inside.
for the price of the lnb 5 euro swap it out.
after that line old or receiver has a problem.
if the receiver does not generate the 22 khz it will stay in upper band or if the 22 khz does not deactivate it will stay in upper.
being that bbc 1 and bbc 2 itv free view are on lower band this could be a problem as well.
lnb's do not have cristals at all.they use the ceramic diletrec chip with a microwave transistor that is the osclator tank.
ghost capacitor of the chip forms the L/C tank for the osclator to run.
just some information
ralph
 

Copecchia

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#20
Are satellite meters like Satlink for example capable of checking for LNB fault as in with a multimeter?