Sky Digibox hackery


IMPORTANT: Please note that you carry out any of these modifications at your own risk, and that these will almost certainly invalidate any guarantee that your box may have.


1. Telephone line connection

Some Digiboxes will give an on-screen message when powered up if the phone line is not connected. My Pace doesn't, my friend said his Grundig does.
Frankly, this is undesired as I don't give two hoots about whether or not I'm missing out on loads of on-line services. Additionally, I live in France so it simply wouldn't work.

Thankfully the line detection is pretty simplistic, so it can be tricked into bypassing this problem. How? Simple - we trick the Digibox into believing that you have a phone line, it is just 'in use' right now.

Fake phone; JPEG 19K
Simply find a phone lead from a modem or old telephone. The Digibox uses the central two pins. The phone line uses pins 2 and 5 (the outer two of the four on the phone jack). This is where things get a wee bit complicated. If your phone lead only has two wires, then pins 2 and 5 will be the ones to connect to. If your phone lead has four wires, then pins 3 and 4 (the middle two) will be the ones to connect to.
In the picture on the right, you can see what I mean. The left-most example is a two-wire phone lead. In this case, the middle pins of the modem (Digibox) end connect to the regular 2 & 5 of the phone jack. The phone lead supplied with the Digibox should be this type of lead.
In the right-most example the middle pins connect to the middle pins. This is a fully-wired lead, commonly used with actual telephones, but not so commonly used with faxes and modems these days. The other two connections are shown in light grey so as not to obscure the diagram.
Here, the middle pins are the ones that we desire, and they connect to the middle two pins of the phone plug, so you should wire your battery to pins 3 & 4...

NOTE that some (rare) two-wire leads use 2 & 5 to 2 & 5. This type will not work.
This peculiar situation has arisen because most modems do not require the 'ringer' and earth line(s) to be connected. In some countries, these lines don't even exist. Therefore, to cut costs, a way was found to economise on the phone lead. Why have four wires inside when two will do?
Wiring; GIF 4K

Take an OLD 9V battery (PP3, the rectangular type) and wire it so +ve goes to one of the pins of the phone jack and -ve goes to the other, as shown in the picture above.
Now whenever the Digibox tries to access the phone line, it will believe the line is busy. Hopefully it will be smart enough to not put the annoying start-up message on-screen if your phone is apparently connected and 'busy'.

Go to the System Test option (in Services) - I think... and when you try this it should report that the phone line is busy. If not, check your battery isn't totally dead. It should be used, but still carry a little bit of charge. If that isn't the problem, then simply swap the wires to the other two contacts on the phone jack.


How it works...
When the phone is 'floating' (no call is taking place), the phone line rests at -48V. This is the ideal figure. It varies slightly from place to place.
When the phone line is in use, the voltage drops. I've measured between 5V and 16V DC. The actual voltage, again, is not so important as the current. Telephones work by forming a current loop, and it is this current that allows the system to work, not the actual voltage.
We use an old 9V battery because 9V is a good figure to use for a start, and also since the battery will be weak, we are less likely to 'cook' anything. This entire idea may work if you hook up a 12V car battery - but given that a car battery has enough discharge power to make a solid metal spanner turn bright red and burn in half (I know, I tried it once - don't ever do this as your battery is likely to explode and cover everything in really nasty boiling acid!), are you so sure you want that kind of oomph presented to the innards of your Digibox? Best to stick with a nearly-flat PP3. :-)

Finally a note - if you plan to play with the phone line, be aware that the ring signal is between 90V AC and 130V AC. It shouldn't shock you seriously, but it will bite and it won't feel at all nice. However, there is always the possibility that it can kill you. So if you think messing with phone lines sounds like fun, please please take the same precautions as you would for live electrics - okay?

It has been pointed out that this tweak could be used to get free pay-per-view movies. This is apparently correct... The Sky card can hold up to four movies which will be credited to you immediately (and you can pay later if the phone line is busy).
The problem? You cannot ever let your Digibox near the phone line, and if you want more than the four movies you have to either cough up the cash or try to persuade Sky that the kittens ate your viewer card. They aren't stupid - the card should live inside your Digibox so how did it get 'eaten'? They might charge you more for the new card than the movies you stole. Is it worth it?
I'd have liked to have seen several PPV movies... Guess what's going to be on BBC 1 this winter!



2. Forced air cooling (internal)

This modification requires you to open up your Digibox. This will invalidate any warranty and also will expose you to hazardous voltages as well as requiring you to competently probe for a power supply source and then tap it.
If you do not feel confident with any part of this - read the following section.
Remember - Digiboxes use 'switchmode' power supplies, which can be lethal for hours after the box has been unplugged. Always use extreme care!

What is it about satellite receivers that the things run so hot? My old analogue Amstrad got almost ridiculously hot. My Pace MSS200 gets itself pretty warm. And the Digibox? It isn't as bad as the Amstrad but it is way warmer than my VCR or my DVD...

Apparently, the fault is due to two things. The power supply is operating near the top of it's capacity. Some people believe a 20W supply operating at 20W is more efficient than a 40W supply operating at half of its capacity. I beg to differ, but I digress. Secondly, the tuner modules run hot. It is perhaps ironic that the man from SatCure says the Digibox CPU in later Pace models is prone to overheating ... as the temperature of the CPU was nothing compared to the temperature of the tuner unit.

This does raise the obvious question - if fitting a fan would improve reliability (especially given that people will do stupid things like stick the box in a closed cabinet, or stack it along with their VCR, PS2, and other boxes) why don't they fit a fan inside the thing?

An "industry insider" who does not wish to be named said what you and I suspected... cost. A hundred thousand units could mean a hundred thousand fans, and even if they could source them for a pound each, that'd be enough to buy a reasonable house overseas.
I did wonder about the costs of 'fault returns' due to not having a fan, versus fitting fans, but we must not lose sight of the fact that it is a technological appliance. Its quoted service life isn't a decade, is it?

In order to aid the cooling of my Digibox, I found a processor fan and fitted it into the space reserved for the expansion module. Here is how...

The fan, installed; JPEG 27K
Above you can see the fan installed. I have taken the 0v connection from the tag mounted to the metal shield around the tuner. This is quite solidly bonded to the metal casing of the Digibox so it seemed as good a place as any for the 0v connection.

On my Digibox, there are four diodes below the power supply. These provide weird voltages such as +8V, +16V, something around +24V and something like -14V.
The fan is rated at 12V, so the safest option is to connect it to the +8V diode. This, on my model (a Pace BSkyB 2500B) is the left-most of the four diodes, the end closest the front of the box. This will run the fan at a comfortable 2/3 of its capacity. It won't exactly chuck out the air (less so since the fan output is partly obscured) but it'll run quietly.
The other option is to run the fan 4V over its rated voltage by hooking it to the +16V diode. This is the right-most diode, the end closest the front of the box. This will positively toss the air out, and possibly blow dust-bunnies around the back of wherever you place your Digibox! I have run my fan this way for quite a while and it coped, however cheaper fans may fail if you run them for too long at this voltage. I only swapped my fan to the lower power as it runs continuously (as long as the box is plugged in, regardless of whether it is 'on' or in standby) and it wasn't exactly quiet...

The picture below shows the four diodes in more detail.

The fan, diodes; JPEG 32K
This describes the power supply of the Pace BSkyB 2500B Digibox.
For other receivers, you'll need to look for something similar and verify it with a good multimeter. IT IS VERY IMPORTANT to be aware that extremely hazardous voltages are present within switchmode power supplies (even after the power has been disconnected). Look only for the diodes and don't just poke around at random in the hope of finding a suitable voltage.

(and if you cannot find suitable diodes, give up while you're ahead)

The diodes are the cylindrical black things with the silver stripe. The stripe shows the 'polarity' of the diode. They allow current to pass in one way only, so are often used to convert AC power into 'rectified' DC and also to prevent power being hooked up back to front.
That's your electronics lesson for the day. :-)

In this picture, the left-most diode provides 8V. You can clearly see the fan hooked up to it.
Ignore the square thing.
There are two more diodes, one 'upside down'. These carry 'weird' voltages, so you'd be best not touching these.
The right-most diode carries 16V.

It is VERY important that you check and recheck that nothing in your wiring is touching anything else. If it is, the best you'll get is a dead and possibly irreparable receiver. The worst? A loud pop and bits of smoking hardware flying across the room.
Obviously, it goes without saying that you perform this modification with the Digibox completely disconnected from everything. Don't decide it is 'okay' to just switch it into standby...

Again, I remind you that this description is for the Pace BSkyB 2500B.

To fit the fan, I was lucky. The fan itself was intended for a Pentium processor (the original type). Once the clip-on harness was removed, the fan itself was less than a millimetre too large for the module slot.
This, as it happens, is an advantage. I put it into the module slot and - ensuring it was clear of all components on the circuit board - pushed it firmly. It is held tightly in place, at a slight angle and I don't need to worry about it coming loose or otherwise rattling around inside the Digibox.

Something I have not covered is air direction. I could have fitted the fan to blow air either way. It is for good reason that the fan blows air out of the box. This takes the warm air from inside the box and pushes it out. More air is sucked through the vents in the Digibox case. Doing it this way may not quite keep the box as cool as forcing air inside, but on the other hand you don't run the risk of the fan sucking anything undesired into the box. If you run your fan over-voltage, it runs the risk of sucking in small metallic objects such as staples. You can imagine how much your Digibox would appreciate that...

The fan, rear view; JPEG 18K
I have not fitted a finger guard as I know the fan is there. If you have children, you might like to fit a guard of some type so fingers can't poke the fan blades; though I myself might feel tempted to fit sharpened metal blades so people who go poking around the backs of things learn very quickly not to do such a thing again - and even if they wanted to, they'd have no fingers. No, seriously... a piece of 0.5mm x 0.5mm plastic netting like the type used in bug screens would be a simple way to mask off the fan. If you plan to use metal mesh like fine chicken wire, I recommend you hold it in place on the outside with some hot-melt glue so as to make it difficult for anything conductive to find its way inside the Digibox.

As you can see, I have replaced the two screws that held the module cover in place. This is so I don't lose them!



3. Forced air cooling (external)

If it looked a bit hairy adding a fan internally, all is most definitely not lost! The simplest method is to get yourself a 9V to 12V fan, and run it from a separate power supply.
An alternate way to cool a Digibox...
In my installation, I have a 12V DC fan salvaged from an old computer power supply unit. It is powered by a tiny 9V unregulated Nokia mobile phone charger. As we are running the fan at roughly three quarters of the rated voltage, it is quite quiet.

As you can see, the television is perched on top of the Digibox (which is on top of my VCR) with a space of about two inches given by books carefully placed so as not to obscure the ventilation slots. The fan has been placed to suck air up and out of the Digibox. This not-terribly-warm air is pushed up into the television, where it helps to keep that cool. Although the Digibox has no vents underneath it, because it remains cool, it helps to keep the video recorder cool. So this one fan, carefully placed, is keeping everything cool.

If your make of Digibox does not have cooling slots across the back, you may be forced to 'pick a side'. My recommendation would be to cool the tuner as a first priority, and then the power supply. In the Pace design, these parts are pretty close.
If you have no idea what's inside your box, put your hands on the top of it. If one part feels hotter, put the fan over the vents closest.
Of course, if your vents are on the side or the back... you're going to have to use a bit of ingenuity. One or two tiny 'processor fans' attached to the side may well do all that you need. Obviously, placing a TV on top of a Digibox on top of a VCR is not an ideal situation. I'm pressed for space. If you stack any of your equipment, you must pay attention to its cooling.

The very worst thing you can do is what many people do in fact do - stack the equipment tidily inside a closed cabinet.
With the permission of a friend, I rigged up a temperature sensor inside such an installation and found that the ambient was 28.5°C (the living room was 23°C), but the narrow spaces in between units measured 36.8°C. I did not take any of his equipment apart, so I cannot provide exact figures of the internals of his equipment. So I went home and measured my own Digibox's tuner at 57.2°C after six hours without forced air cooling - yes, too hot to keep a finger on!
Imagine how hot the thing would be in an enclosed space with the conductive ventilation obstructed. I would imagine temperatures in the order of 75-85°C would not be untenable. This, of course, will have an affect on the life of the component - not to mention the life of components nearby, especially the electrolytic capacitors.



Your ideas...

If you have made any useful modifications to your Digibox that you would like to share, please get in touch.


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Copyright © 2006 Richard Murray