Listen Up Dead DiSEqC Switch

Lazarus

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I goosed a 2 Port DiSEqC switch yesterday whilst augmenting my house-wide distribution system to include DTT by the use of a UHF Splitter and a couple of Sat/TV Combiner/Splitters.

Did a test run in the dry as it were, in a room where the one pre-existing cable from the Yagi ran alongside a Satellite feed. All worked.

When the hail stopped long enough, I then went out to fit them in their intended place in a sheltered spot near one of my DiSEqC switches.

Having failed to disconnect power from any and all devices vaguely connected to the system, I discovered too late that stray "stuff" (A tingle, no less) was present.

No biggie, as they are only a couple of quid, but a reminder to the gung-ho amongst us not to fanny about connecting and disconnecting stuff with it live .... even if it does only involve otherwise harmless voltages.

Far from enhancing our viewing flexibility, I denied Sat to the front room as the switch failed stuck on Port B.

The point is, we all know how we should go about things, but human nature creeps in, in the enthusiasm to finish the job and put a smile on SWMBO's face.

Fortunately I had a spare, so all is now well.
 

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Ahh a sad lesson learned, good thing you had a spare....On some devices when you turn the front panel power off or off with a remote, there still could be DC power out to the LNB or switch, it is best to use the power switch on the back or pull the power cord from the wall or AC to DC inverter before messing with any coax connected to a satellite box or related equipment.

And if the main driving force behind getting the work done as soon as inhumanly possible says to it faster my show is on in 5, then have them hold the open end of the coax, tell them to watch for the excess DC voltage that may come flowing out if you accidentally left the power on, you will be reminded several times a second to be sure to look and see if the power cord is unplugged.

I cant remember on how many switches I've had to go replace simply because someone thought that they could re-rout this coax a bit better then the way it is now, and nothing would happen if it was a quick disconnect, re-connect.
 

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As a matter of interest, does anyone know how a DiSEqC switch actually works? Presumably there's a small, integrated circuit of some sort and maybe a relay?

It's one of those things we commonly use, but take for granted.

In the vain hope the failure was due to a sticky relay, I gave it the Manchester Screwdriver treatment, but no joy.
 

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I goosed a 2 Port DiSEqC switch yesterday whilst augmenting my house-wide distribution system to include DTT by the use of a UHF Splitter and a couple of Sat/TV Combiner/Splitters.

Did a test run in the dry as it were, in a room where the one pre-existing cable from the Yagi ran alongside a Satellite feed. All worked.

When the hail stopped long enough, I then went out to fit them in their intended place in a sheltered spot near one of my DiSEqC switches.

Having failed to disconnect power from any and all devices vaguely connected to the system, I discovered too late that stray "stuff" (A tingle, no less) was present.

No biggie, as they are only a couple of quid, but a reminder to the gung-ho amongst us not to fanny about connecting and disconnecting stuff with it live .... even if it does only involve otherwise harmless voltages.

Far from enhancing our viewing flexibility, I denied Sat to the front room as the switch failed stuck on Port B.

The point is, we all know how we should go about things, but human nature creeps in, in the enthusiasm to finish the job and put a smile on SWMBO's face.

Fortunately I had a spare, so all is now well.
Wot ??
You have a spare SWMBO ..?
Is she ok with this ?
 

Lazarus

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Terryl

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As a matter of interest, does anyone know how a DiSEqC switch actually works? Presumably there's a small, integrated circuit of some sort and maybe a relay?

It's one of those things we commonly use, but take for granted.

In the vain hope the failure was due to a sticky relay, I gave it the Manchester Screwdriver treatment, but no joy.
Screwdriver or BFH....It still will be FUBAR, a Diseqc switch is basically a transistorized switch controlled by a 22 kHz tone or tone pulses telling it what port to activate.

It also supplies DC power to the selected device or devices, if you have an understanding of electronics here is a simple schematic diagram of one.
diseqccirc2.png

The satellite receiver (connected to port XS1) selects the proper LNB by sending the switch a series of 22 kHz pulses, this input port also supplies the necessary DC power to run the switch and the attached LNB's.

The Diseqc decoder IC (DD1) decodes the commands and selects the proper port by turning on a set of power transistors, this turns on the correct LNB by supplying the DC power it needs to run, some LNB's also use a DC switching voltage to select the correct transponder polarity, the switch does not care what the DC voltage is, it just supply's what DC voltage what is coming in on the input, this could be +14 or +18 volts DC.

Now when the switch has turned on the correct LNB it has a direct signal path back to the receiver, the other LNB's are tuned off, so they can affect the signals from the selected LNB.

Now a multi receiver switch is far more complicated then this simple single receiver to 4 LNB's switch.

If you want me to tell you how that type works it will cost you a case of Scotch and you will have to wait till I find my professors hat.
 

a33

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Just to add:
Now when the switch has turned on the correct LNB it has a direct signal path back to the receiver
This signal path goes through the PIN-diodes, in the right of the diagram above.
Very ingenious setup with the PIN-diodes, I think, but that is mainly because I never had much knowledge of RF switching and PIN-diodes before I 'studied' Diseqc switches. :)

BTW A blown Diseqc switch as far as I know is usually caused by:
- blown transistor (one port won't switch on, or is always 'on'), or
- blown IC (switch doesn't react to switching commands at all).
A blown transistor can be replaced by another, if you want. For more expensive (diseqc 1.1/uncommitted) switches that might be worth the try. ;)
I've never done such repairing, though; I've never had a blown diseqc switch.....

Greetz,
A33
 

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Good work chaps.

Yes, I have a degree in electronics, but in my day thermionic valves were still mainstream ...... :D
 

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Not quite a degree here but a diploma .. not once were valves mentioned during my 2 year course. I have a perfect understanding of how transistors work but valves are an enigma. Other than the fact they took about a minute to warm up.
 

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Not quite a degree here but a diploma .. not once were valves mentioned during my 2 year course. I have a perfect understanding of how transistors work but valves are an enigma. Other than the fact they took about a minute to warm up.
OTOH, in my time at Leeds Uni doing the mainstream "heavy electrical engineering" course in 1966-69, transistors were never mentioned during the 1st year and only peripherally thereafter (which was a big disappointment to me as I was just "getting into" them).
However, on the subject of these switches:
- some (the cheap "BEST" ones in particular) just don't work properly even when new (as I found out this time last year, as described in a thread I started on the forum)
- "luckily" having connected and disconnected those and others, I hardly ever powered down the receivers, and have never yet "blown" the switches - matter of "luck" or what?
 

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6v6.jpg
Well at least you can discuss triodes and pentodes with me G ..
I was weened on 'em ..
My favourite all rounder is still the octal based 6V6
 

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May I put a word in for the often overlooked power tetrode?
 

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Another old favourite of mine ..
The Power Tetrode 807 ..
This one would happily produce several watts of RF at its anode ..and was in fact the ,meat, of the first medium wave transmitter I ever built back in my yoof
807.jpg

When a ballance tank cct was used at the output ..you could draw a healthy arc from the cap with your finger ..or better ..a screwdriver..
Unbalanced (untuned) it would glow a nice purple inside the glass envelope..
lol
 

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FWIW (probably not a lot :D) I suppose it was playing with valves (notably an old multiband receiver without any case!) before I went to Uni is what made me less scared of high voltages than "some" - "mains" is relatively trivial and a couple of kV needs a little care (and can give you quite a belt/burn!), but 50kV does need quite a lot "attention" (luckily never "experienced the full force" of that) :D
 

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Unfortunately I lost a colleague to a 500,000 watt tube TV transmitter, he was on his way out of town going on vacation when he got the call from the studio saying the the transmitter will not come up to full power, so he swung by and went in to take a look, he told the wife and kids it may take about 15 to 20 min, he looked and saw that the main output tubes were acting up, in his hurry he forgot to discharged the high voltage side of the cabinet, he reach in to reset them (we think) and POW......150 KV.........His wife waited for about 30 before she went in to look and see what was taking so long, you all can figure the results.

So I use to play around with some very big tubes, at some very high power levels, the next week we purchased a solid state transmitter, and named the transmitter site in his honor, we junked the old one per his wife's request, she got to see it being crushed by a bulldozer.
 

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Just to add:

This signal path goes through the PIN-diodes, in the right of the diagram above.
Very ingenious setup with the PIN-diodes, I think, but that is mainly because I never had much knowledge of RF switching and PIN-diodes before I 'studied' Diseqc switches. :)

BTW A blown Diseqc switch as far as I know is usually caused by:
- blown transistor (one port won't switch on, or is always 'on'), or
- blown IC (switch doesn't react to switching commands at all).
A blown transistor can be replaced by another, if you want. For more expensive (diseqc 1.1/uncommitted) switches that might be worth the try. ;)
I've never done such repairing, though; I've never had a blown diseqc switch.....

Greetz,
A33
Relevant to my question. I have 3 blown already. Can't get somebody to repair. How do I minimize blowing out?
 

a33

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Welcome to the forum, @Amosmoni !

I have 3 blown already. (...) How do I minimize blowing out?

How did they blow out?
Did you connect or disconnect LNB cables, with receiver power supply still connected to the power?
Is there a motor connected (and how/where in your setup)?

Greetz,
A33
 
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Amosmoni

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Welcome to the forum, @Amosmoni !



How did they blow out?
Did you connect or disconnect LNB cables, with receiver power supply still connected to the power?
Is there a motor connected (and how/where in your setup)?

Greetz
Three is no motor.its possible I do connect and disconnect LNBS when power is on.
 

a33

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its possible I do connect and disconnect LNBS when power is on.

That is not a good idea.
While doing that, it is possible that the center pin of the F-plug (which carries voltage, with some receivers even in standby mode!) briefly touches the 'earth/mass' of the system, thus causing a brief shortage. That is often the cause for a diseqc switch to be blown.

So rule of thumb is: always pull the power cord, when working on your system.

I sometimes don't pull the power cord, but in cases like that I very, very carefully disconnect and connect the cables, as to not touch the earth/mass with the center pin. I don't advise this method; especially not when you have to work on more than one cable!
So it's best to always unplug your receiver.

greetz,
A33
 

Amosmoni

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That is not a good idea.
While doing that, it is possible that the center pin of the F-plug (which carries voltage, with some receivers even in standby mode!) briefly touches the 'earth/mass' of the system, thus causing a brief shortage. That is often the cause for a diseqc switch to be blown.

So rule of thumb is: always pull the power cord, when working on your system.

I sometimes don't pull the power cord, but in cases like that I very, very carefully disconnect and connect the cables, as to not touch the earth/mass with the center pin. I don't advise this method; especially not when you have to work on more than one cable!
So it's best to always unplug your receiver.

greetz,
A33
Thank you so much for your technical advice. I will follow it and see the difference.
 

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