No signal from freesat box when coax shield connected

[Findlay2]

I have encountered a strange thing lately. My old Grundig freesat box wouldn't switch on properly, just a flickering green light on the box and no output from the scart to the TV. I just bought a cheap new Teknikal box which also didn't seem to work. It switched on but no signals detected. in desperation I disconnected the antenna lead and cut it back about 6 inches thinking it may have broken. For some reason I did not fit the plug on the lead, just held it up to the input and pushed the centre core in. The box then worked fine tuning to all stations. But it stopped working if i connected the outer shield, no stations or signal. I found the old Grundig box showed a proper stable green light with the input disconnected and worked fine on just the central core, but packed up when the outer core was connected. Anyone any idea what is going on? It is difficult to fit an f plug and not use the shield part of the cable. The feed comes from a quad detector. 2 other cables go from the dish to a Humax box which works fine.

 

[ozumo]

If the Humax is unplugged from power does the Grundig work with the ground coax shield connected?

 

[a33]

And another question: Is the centre core not too long? That is, not sticking out more than 2 to 3 mm from the F-plug?

Could be that the centre core sticks in too far in the receiver, when the F-plug is screwed on; thus causing a shortage.

Greetz,
A33

 

[Findlay2]

Thanks for your quick replies guys. I've done the experiment with the Humax unplugged. Both the Grundig and the Teknikal boxes work fine without the shield connected. When I connect the shield the Grundig immediately switches itself off and can't be brought back on. The Teknikal loses the signal but at leases stays powered on. The centre core is fairly short - as you see in the demos showing how to do it. Something weird seems to be going on.... Any more thoughts? I guess I can live with it, if it isn't dangerous, but attaching an f-plug without it going properly over the shield is difficult. At the moment I have a bodge where I cover the outer sleeve with insulating tape but can't keep it like this as it doesn't grip very well. Can you buy f connectors which clamp down on the outer sleeve, a bit like the old TV style coax type ? I've seem compression F connectors but it seems you have to buy a special tool to use them.

 

[Channel Hopper]

Is one or more of the boxes on a different floor level ?

 

[a33]

When I connect the shield the Grundig immediately switches itself off

This phenomenon would normally indicate a shortage/over-current protection of the receiver, I would say.
However, when there would be a shortage in cable or LNB-output, I cannot explain why there is normal reception with cable shield not connected to the receiver.
So I am a bit puzzled.

Do you have single output LNB, or twin or quad?

Greetz,
A33

 

[Findlay2]

Is one or more of the boxes on a different floor level ?

No, both boxes are on same floor. The Humax takes a two cable feed from the dish to the front ground floor room, about 20- 25 feet in all, the Grundig takes a single cable feed from the same dish to the back ground floor room, about 15-20 feet longer

 

[Findlay2]

I'm pretty sure it is a quad - at least that is what I asked the installer for about 11 years ago when the Grundig was installed, a few months after the Humax. It worked fine for ages. I hadn't used it for a couple of years before switching it on last week. Because it wouldn't switch on at all, just showing a flickering green light on the front panel, bought the Teknikal box to replace it. The Teknikal switched on but wouldn't tune, so I set up in the front room using one of the feeds to the Humax to test it and it tuned OK. When I connected it up in the back room, again no signal. So I took the f-connector apart to check it - seemed fine so I just fed the central core into the Teknikal input and suddenly got a signal and it showed normal TV sound and vision. When I touched the shield wires to the input surround the signal went. I Then switched on the now disconnected Grundig and found the green on light was working ok. I got this to work again by just connecting the central core. When I touched the shield wire to the outer of the socket it lost signal and switched off.

 

[Channel Hopper]

Just as a test, if your Griundig has a 'figure of eight' plug in the back, try reversing it.

 

[Trust]

Just a thought .
Do a test with a ohm meter , see if there is a short between centre core and the shield .
If the shield somewhere is broken and there is no shieldconnection with the lnb and the shield is touching the core , could be the cause of the trubble .
Lnb gets his ground from the other receiver(s) and give his signal still trough that faulty cable .

 

[a33]

And when you don't have an ohm-meter, maybe these tests give extra diagnostic information:

1. Disconnect the cable of your receiver at the LNB. Then switch on the Grundig without cable, and connect the cable at the receiver. Does it again switch off immediately, again? Then the cable seems to be at fault (shortage, or water ingress?).
(I assume you can determine, which cable of the LNB goes where...?)

2. When you swap cables at the (quad) LNB outputs, does the problem stay the same? Or does the problem 'follow' the specific LNB output?

Greetz,
A33

 

[Findlay2]

Just as a test, if your Griundig has a 'figure of eight' plug in the back, try reversing it.

Thanks - it doesn't have a "figure of eight" plug, just a hard wired mains cable

 

[Findlay2]

Just a thought .
Do a test with a ohm meter , see if there is a short between centre core and the shield .
If the shield somewhere is broken and there is no shieldconnection with the lnb and the shield is touching the core , could be the cause of the trubble .
Lnb gets his ground from the other receiver(s) and give his signal still trough that faulty cable .

Thanks - have just measured the resistance between the centre core and the shield. It comes up as 3.9 Ohms so looks like a short somewhere!

 

[Findlay2]

And when you don't have an ohm-meter, maybe these tests give extra diagnostic information:

1. Disconnect the cable of your receiver at the LNB. Then switch on the Grundig without cable, and connect the cable at the receiver. Does it again switch off immediately, again? Then the cable seems to be at fault (shortage, or water ingress?).
(I assume you can determine, which cable of the LNB goes where...?)

2. When you swap cables at the (quad) LNB outputs, does the problem stay the same? Or does the problem 'follow' the specific LNB output?

Greetz,
A33

Thanks for this. I haven't got a high enough ladder to get up to the dish so can't test for this. Seems like I have established a short by measuring 3.9 Ohms between the core and shield on the cable.

 

[a33]

So, hopefully you can find the location of the short easily; maybe where the cable makes a sharp bend or so?
Otherwise you still need to get up a ladder.... :-(

Greetz,
A33

 

[PaulR]

A common place for shorts to occur is where the F-plug is fixed to the cable, especially the screw-on type plugs. A single whispy thread from the braid can easily short across to the centre wire.

 

[Findlay2]

A common place for shorts to occur is where the F-plug is fixed to the cable, especially the screw-on type plugs. A single whispy thread from the braid can easily short across to the centre wire.

Thanks again guys. I've already cut back about 6 inches from the original length, carefully reattached the plug and still got the problem. There is a bend about 3ft back, so maybe the short is here. I'll have to get an extension lead before I cut back to here, so will be a few days before I can report back. While I'm ordering, can anyone suggest a higher quality F-connector rather than the screw type? I think these are awful. Is there a compression type that you don't need a special tool for?

 

[Channel Hopper]

Compression needs a tool, as do crimp.

Screw on types are fine, as long as you get the good ones.

There are plenty of bad versions out there, if they weren't metal I would think they were 3D printed.

 

[a33]

1.
You can wiggle the cable where the bend is, while you do the ohm measuring.
When the short then disappears, likely the bend causes the problem.
(Though you cannot use this reasoning vice versa: when the short does not disappear, there is no garantee that the short is NOT there...)

2.
After cutting the cable, you don't have to put on a new F-plug, to do your ohm-measuring again. You can measure your cable at the LNB side, and the small part on your receiver side....

3. (Added later)
I use a tool to screw on the F-connector to the cable, the T-form type e.g. here:
xxx.amazon.nl/F-stekker-opdraaiset-opdraaihulp-3-delige-montagesleutel/dp/B00NHQG4K4/ref=asc_df_B00NHQG4K4/?tag=nlshogostdde-21&linkCode=df0&hvadid=454882191249&hvpos=&hvnetw=g&hvrand=5235926014375045991&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9103798&hvtargid=pla-423167048148&psc=1
It makes the screw-on F-plug much more useable, I find.


Greetz,
A33

 

[Findlay2]

1.
You can wiggle the cable where the bend is, while you do the ohm measuring.
When the short then disappears, likely the bend causes the problem.
(Though you cannot use this reasoning vice versa: when the short does not disappear, there is no garantee that the short is NOT there...)

2.
After cutting the cable, you don't have to put on a new F-plug, to do your ohm-measuring again. You can measure your cable at the LNB side, and the small part on your receiver side....

3. (Added later)
I use a tool to screw on the F-connector to the cable, the T-form type e.g. here:
xxx.amazon.nl/F-stekker-opdraaiset-opdraaihulp-3-delige-montagesleutel/dp/B00NHQG4K4/ref=asc_df_B00NHQG4K4/?tag=nlshogostdde-21&linkCode=df0&hvadid=454882191249&hvpos=&hvnetw=g&hvrand=5235926014375045991&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9103798&hvtargid=pla-423167048148&psc=1
It makes the screw-on F-plug much more useable, I find.


Greetz,
A33

Thanks again guys. I've tried wiggling the cable at the bend while connected to the meter and no change. I'll get an extension lead and cut back 6ft or so and see if this does it. Thanks for the link to the tool!