Weird failure

[B.J.]

The last couple days, it has seemed to me that my C-band wasn't quite as good as it had been even a week ago, but I figured that I still wasn't quite in alignment.
Well yesterday, I tuned in G28, and watched my NFL game on an S2 channel, so it wasn't working TOO terribly.
Today, I tried locking a channel on AMC-6 that I had tuned on Saturday, but I got absolutely NOTHING. Tried 2 or 3 other transponders. NOTHING. Moved the dish back to G28, where I had been. Tried to tune in Huskervision and Pentagon. NOTHING. Moved the dish to G17, looking for the analog Classic Arts.... NOTHING. I also noticed that there seemed to be a strange analog signal on 3 channels, regardless of which sat I was on, something similar to what I had seen once before when one of my LNBs would go into oscillation.
I tried switching receivers. NOTHING on 4 different receivers.
I thought maybe the master receiver wasn't providing LNB voltage. Checked and found 18V coming out of the receiver.

THEN, I hooked up my Channel Master meter, which has an AMP meter function, and it showed ZERO current going to the LNB! So I went out to the dish, pulled off the coax, and checked the voltage. Only 5V at the end of the coax!
I had checked the LNB voltage on Saturday, and it was 18V.
I looked around, and can find NO indication of any damage to the coax out at the dish.

Anyway, I switched C-band over to the Ku coax, and it's working again.

It just seemed really weird that my coax was OK yesterday, then all of a sudden today, it just stopped working.

Now, my problem is finding WHERE the coax is bad. It would be nice if it was just a bad connection out at the end, but I have a suspicion that I may have damaged the coax by pulling it through a tight space, right in the middle of the run.

Anyway, I have some troubleshooting to do here. Hopefully I won't need to run a whole new coax. I think in the meantime, I'll run the Ku over to an unused port on my diseqC switch at my Fortec dish.

 

[Anole]

good one

As I was reading through your symptoms, I was thinking:
... diseqc switch, diseqc switch, coax connector...
It wasn't clear where your diseqc was, but if it's out at the dishes, then I still like it.
But "bad connector on the coax" really works for me, too.

That "no current" is a give away.
The 5 volts is probably just meaningless leakage either through the switch or a bad solder joint, or a crimp.

Without seeing a schematic of how you're set up, I wouldn't want to offer a serious opinion,...
... but the switch or connector sure seem like glaring candidates to me. -
Let us know! - :up

 

[Corrado]

I have wasted time with the voltage test here. The trick is testing with current draw also. Otherwise one strand of conductor might be passing the voltage under no load conditions with a digital high impedance meter.

 

[B.J.]

As I was reading through your symptoms, I was thinking:
... diseqc switch, diseqc switch, coax connector...
It wasn't clear where your diseqc was, but if it's out at the dishes, then I still like it.
But "bad connector on the coax" really works for me, too.

That "no current" is a give away.
The 5 volts is probably just meaningless leakage either through the switch or a bad solder joint, or a crimp.

Without seeing a schematic of how you're set up, I wouldn't want to offer a serious opinion,...
... but the switch or connector sure seem like glaring candidates to me. -
Let us know! - :up

Well, there was no switch in the ciruit at all. LNBs connected straight to my receiver, except it did go through a power pass splitter which I bypassed when I started testing. However my testing has really hit a confusing symptom, which I'll talk about below....

I have wasted time with the voltage test here. The trick is testing with current draw also. Otherwise one strand of conductor might be passing the voltage under no load conditions with a digital high impedance meter.

I agree with this completely, and I generally test voltage with my channel master meter, which measures voltage and current while powering the LNBs, so it was under load. Saturday I got 18V. Today, even before I could connect the LNB to the meter, the meter was saying only 5V.

Well, I tried to determine whether the center conductor or the shield was faulty, so I did an experiment. And the results are a bit confusing.

I shorted the center to the shield of the "faulty" coax back at the receiver, and also connected both to the shield of the "good" coax. I then checked the resistance out at the dish.
I got ~ 1500 ohms between the center and shield of the bad coax.
I got ~ 300 ohms between center of the bad coax and shield of GOOD coax.
I got ~300 ohms between shield of bad coax and shield of GOOD coax.

I then disconnected the good coax, shorted shield and center at receiver end. Checked the resistance, and it was about 11 ohms.

The 11 ohms sounds logical for a good coax, and the 340 ohms makes sense for either the center or the shield for a bad coax, but I can't believe that BOTH would be 340, and I was expecting the 1500 to be twice 300, but instead it was more. This sort of suggested that it's a semiconductor type conductivity of some sort, ie different dependent on the direction of the current, so I reversed the polarity of the tests that gave 300 ohms, and sure enough, one gave something close to 600, but the other polarity gave something like 1500 ohms, PLUS, you could see a capacitive charging/discharging occurring, ie the resistance changed over a period of about 10 seconds while it built up to the steady value. So I'm thinking that I broke the conductor somewhere, but I'm getting conductivity through corrosion or some dielectric or something which is polarity dependent. Anyway, it's pretty clear that the coax is bad. I tried pulling out the center conductor, in case it was broken near the end, but it was solid. Also cut off a couple inches of coax at the dish end, and still got the same readings.

So the coax is clearly bad. I think it's only hope is for me to cut it in the middle, hoping to find the place where I damaged it, but I think that will have to be put off while I'm fixing other things.

 

[Kallesatman]

The prairie dogs wanted satellite tv and they tapped your coax.

 

[B.J.]

The prairie dogs wanted satellite tv and they tapped your coax.

Around here it would be chipmunks and porcupines as the likely culprit. Between the chipmunks, porcupines and mice, they've done thousands of $s of damage, including emergency visits to vet to remove quills from my dog's face.

But I couldn't see any obvious damage anywhere the animals had access. My best quess is that I did the damage myself, pulling the big ribbon cable through some rather small tight holes.

 

[brex2001]

I then disconnected the good coax, shorted shield and center at receiver end. Checked the resistance, and it was about 11 ohms.

The 11 ohms sounds logical for a good coax, and the 340 ohms makes sense for either the center or the shield for a bad coax, but I can't believe that BOTH would be 340, and I was expecting the 1500 to be twice 300, but instead it was more. This sort of suggested that it's a semiconductor type conductivity of some sort, ie different dependent on the direction of the current, so I reversed the polarity of the tests that gave 300 ohms, and sure enough, one gave something close to 600, but the other polarity gave something like 1500 ohms, PLUS, you could see a capacitive charging/discharging occurring, ie the resistance changed over a period of about 10 seconds while it built up to the steady value. So I'm thinking that I broke the conductor somewhere, but I'm getting conductivity through corrosion or some dielectric or something which is polarity dependent. Anyway, it's pretty clear that the coax is bad. I tried pulling out the center conductor, in case it was broken near the end, but it was solid. Also cut off a couple inches of coax at the dish end, and still got the same readings.

So the coax is clearly bad. I think it's only hope is for me to cut it in the middle, hoping to find the place where I damaged it, but I think that will have to be put off while I'm fixing other things.

IF you think you must cut the coax somewhere near the middle then perhaps this might help.
I've had some experience troubleshooting low voltage electrical control circuits as a maintenance mechanic/electrician. Here is something used to detect shorts in wiring. It could be used to determine where an open is located by deliberately shorting out a section of the circuit. Like a straight pin through the coax near the suspected point of damage.
One simple tool that I've used is a simple 12 V automotive turn signal flasher, a low wattage 12 V lamp & a 12 V UPS battery to put an load on the suspected damaged wiring. One end of the circuit is connected together while the other end is powered with this improvised tester. A small hand held inductive ammeter is place over the wiring to indicate current is flowing through the wiring for the complete length of the circuit. Included pics of an ammeter for clarity. These are more commonly used to quickly check automotive charging & starting circuits.
The ammeter needle will fluctuate at the same rate as the flasher. If the circuit had a short between conductors the needle would stop moving just beyond the short.
If your "open" circuit is in the coax shield, then it may not conduct enough current to operate the flasher because only a few strands are holding hands. A deliberate short nearer the tester would cause the flasher to operate. You would have to take a guess where to start.
If it were me I wouldn't want to splice in a new piece of coax to an existing run of ribbon cable unless I could be certain it was well connected & weatherproofed.
Hope this helps someone with a "shortage". Pun intended.

 

[Kallesatman]

Is the coax inside pvc pipe, what diameter and how long of a run is it?

 

[B.J.]

My coax run is ~250', of which about 150' is indoors. Goes from one end of my basement to the other side of the house, then up along pipes up through the main floor to the attic, then over through a crawl space into my garage's 2nd floor, then down to ground level, outside to a PVC conduit, which is about 50' to where my Fortec dish used to be, then it's open, waiting for me to bury the cable over to where my BUD is. The part in the PVC is probably not damaged

That meter brex describes sounds neat, I've been looking for an affordable AC version for another purpose. However my coax doesn't appear to be shorted, it's more of a partial open. I think I may try using the pin through the insulation into the shield method, shorting the end of the coax to the house ground, then use an ohm meter with a pin to the shield, until I find the point where the resistance increases. I'm pretty sure that I know ~ where the coax was damaged, because I really had to pull on it hard to get it through this one small hole that I have to feed several cables through one of the main support beams for my house... ie I didn't want to drill too many holes through these beams. The place where I think I damaged the cable is in my shop, near cold water pipes I can use to test resistance with the pin to the shield, so I think that's the best route. If I locate the break there, I can splice in another section from there to my receivers. It still seems weird to me that both the center conductor and the shield were damaged though, and just on one of the two coaxes, ie this is ribbon cable with 2 RG6, and a bunch of dc lines for the actuator and polarotor, and all that's damaged is the one coax. I'm probably going to run new coax eventually, but even if I do, I'm still going to try to use the old one for my fixed dish, assuming that I can find the point where it's damaged.

 

[rv1pop]

Squirels in the attic???? Those critters got my cable tv, antenna tv and phone lines at my old house. I have an MFJ antenna analyzer for ham radio and it has a coax tester. It can locate a fault in the cable. As I recall it finds shorts within a foot and breaks within 3 feet. There are calculations to do but they are not that hard to do. Check with a local ham club or store and see if you can borrow one -- maybe with its' owner/operator!

 

[B.J.]

Squirels in the attic???? Those critters got my cable tv, antenna tv and phone lines at my old house. I have an MFJ antenna analyzer for ham radio and it has a coax tester. It can locate a fault in the cable. As I recall it finds shorts within a foot and breaks within 3 feet. There are calculations to do but they are not that hard to do. Check with a local ham club or store and see if you can borrow one -- maybe with its' owner/operator!

Well, we definately have mice and squirrels in the garage, where the coax goes through, but I didn't see any obvious damage. I did have squirrels or mice eat the wiring in my outboard motor that I used to store outside. Launched the boat the next spring, and the darn thing wouldn't start. Opened up the top, and saw all these chewed up wires. Twisted a couple together and the thing started right up.

I almost bought one of those antenna analyzers several years ago, but I hardly ever get on the air anymore, so it's not worth it for me to buy one. I was thinking about transmitting into the cable, then going around in the dark with one of those night vision things that lets you see via infra red. I read a post from one ham once who found some bad connections in his transmission lines by using a video camera that was sensitive to IR, and seeing the connections heat up when he was transmitting.

I checked the shield of my coax from about 100' from each end using the pin through the insulation into the shield thing someone mentioned. The shield seems good every place I tested it, although I still have to test the 75' or so in the middle, which just happens to be a section that runs over my automatic garage door openers, and I seem to remember once that the cable got caught in the garage door once. I guess I'll look more carefully at that section.