LNBF overheats and quits

#1

While waiting for Dreamcatcher 3.01 system, I’ve been playing with Direct TV dish I don’t use anymore. I mounted it on wood board on ground. It’s 20 x 18". Removed the triple LNB and replaced it with a single MK1-PLL. Power is fed via a 20 volt PS up the RG-6. It’s designed for satellite TV. Has 2 F-type jacks, power Out and receiver In. Connected regular RTL-SDR dongle to receiver In. USB of dongle connects to PC running SDR#.

Anyway, after working a few days, now not seeing much on screen. Felt LNBF connector. Plenty warm, almost too hot to touch. Read specs. Says current max is 135 ma. Measured current using an old piece of RG6 with connectors. Opened center conductor up and measured current of 270 ma. Got to be bad. Sent it back through Amazon and ordered new one. Now seeing 110 ma. Seems to be OK now. Don’t know what happened, but have read some LNBF’s are prone to failure. Moral of story, handle your future LNBF carefully!

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#2

Sometimes modern but not so well designed electronics can be damaged due to static discharge or other unwanted voltages. I could imagine that an LNB gets damaged when it is mounted sort-of-grounded and then a coax cable (F connector) is plugged in that is connected to another system that is floating or has a mains input filter but is operated ungrounded. The capacitors in the mains filter work as a capacitive divider that puts half the mains voltage (at high impedance) on the ground line of the circuit, which could damage the LNB when the center connector makes contact before the ground (shield). Which of course it does when F connectors are used.
So, it would be prudent to unplug the receiver from the mains when connecting or disconnecting the LNB.

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#3

pe1chi
This is truly the case with F type connectors. Never thought about it. Really a poor connector design today. That’s probably what happened, for I was connecting this and that, And most likely I had PS connected. Usually I do disconnect PS. But, it only takes once! Thanks sir. w6rwn

#4

@donde I was thinking about this … Your power supply is meant for a SWiM system.

Is the Maverick MK1-PLL rated at 13/18V ? Can it handle 20V?

–Konrad, WA4OSH

#5

Konrad
Well, the specs say this :
Polarization Switch V = 12 - 15VDC
H = 16.5 - 20VDC

I believe you have the same one. I probably zapped it changing cables with power on. New one seems OK, but I’m being real careful.

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#6

I have the same LNB. But I’m feeding it with a 15v lab power supply into a bias-tee. I’m running it at 13v and set the skew and polarization manually.

–Konrad, WA4OSH

#7

20v is a bit high. You also need to take particular care with F connectors that a strand of the outer braid does not wrap around the centre conductor.

Normally LNB’s are very reliable and only need to be replaced due to water ingress or UV damage. External F connectors should be covered with self amalgamating PVC tape.

I have seen wasps living in a LNB with a cracked cover. Not sure if it caused a buzzing sound on the receiver.

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#8

I was thinking about that. This is the PS I’m using.

https://www.amazon.com/gp/product/B06ZZHZPHW/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

Right now it seems to be OK. I’m running 24/7 till hear new Dreamcatcher 3.01 ships. I believe board will have H & V switching built-in. So won’t need PS.

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#9

If you are using it with a broadcast satellite receiver that normally provides the power so you should not need a power unit. The power unit you have is really for a different LNB. Maybe worth metering its output too as sometimes the voltage is higher than what the spec says.

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#10

Jimwatt
You are right! The 2nd MK1 did work, now now not very well. Looks like gain has dropped way down. Current just a bit less at 105 ma. Was 110 ma. I know not much change. Only seeing about 2.8 SNR on same Galaxy 19 I saw 15 SNR earlier. The PS/inserter I have is this one:
AT&T (Formerly DIRECTV) 21 Volt, Black Power Supply, for SWM3, SWM5, DSWM13, DSWM21, and DSWM2RB LNBs. Used for All DIRECTV SWM LNBs (PI21) Measured out voltage 20.5. The H voltage for the MK1 is 16.5 to 20.0. I figured it could handle it. Maybe a spike did in the MK1. Think I’ll return both PS and MK1 to Amazon. And just quit playing around and wait for the new DC 3.01. Did learn how to orient a dish on the outside round glass table! Konrad did right thing: Got a mini-circuits bias-tee and controllable bench supply for the MK1.

#11

Yes, I did mention that the 20v from the SWIM power supply might be a bit much for the Maverick MK-1 PLL. :wink:

I realize it won’t be needed when the DC3 comes out, but I also rolled my own bias tee. It’s useful for a number of things. It turned out almost as good as the mini-circuits, but it’s not shielded. I will post pictures and a schematic if you all are interested.

Also I bought a Freesat V8 Satfinder. I’m looking at setting up a dish (converted to FTA with the MK1-PLL), about 50ft of RG6 and using a splitter with DC bypass on one side and isolation on the other. On the isolated side, I’m going to insert enough attenuation to simulate what the DC3 will need. I’m looking on that side with my SDR to see what signals I see as I switch the satellite tuner from H to V and 22KHz on / off. I did go ahead and also order an analog sat finder meter to help orient my dish.

I’m a bit concerned with the skew adjustment for satellites that are not exactly due south of me (121 deg).

–Konrad, WA4OSH

#12

To get the angle use http://www.dishpointer.com/ which also gives you the skew.

However, first find the satellite and the skew is the final adjustment.

I bought a Freesat V8 and have only used it once but it seems a good tool and beats sitting on a roof in the hot sun with a television and a satellite receiver in a cardboard box for shade :slight_smile: 50ft of cable is fine as the drive from a LNB is high enough to deal with any loses on the cable. One thing I do now is to fit a length of cable from the LNB to the back of the dish and have a joint there using two F connectors and a barrel so if I need to adjust it afterwards I don’t need to get at the LNB. I’m normally using larger dishes 1m or 1,2m so that helps. Everything is covered in self amalgamating tape and the cables are tied firmly to the LNB arm with black cable ties. I also arrange the cable coming out of the LNB to go down and then up so rain runs off rather than than down the cable. The new upcoming receiver promises power for the LNB and the Freesat V8 also provides power.

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#13

The skew might be a minor issue for the DC3. The LNB pointing fixture may need to make allowances for setting it.

–Konrad, WA4OSH