How do cable boxes work ?

[edgerobber]

I think the title says it all - I was wondering how that not so little black box works.
I have seen some mention of the workings in other threads, but I wanted an overall picture (non pixellated )
Some more specific random questions are :[list=1][*]Why does it put out so much heat ? - I know that any electronic equipment will get hot and it is passively cooled and all, but it does seem to get a bit hotter than my hifi kit.[*]How much power does it use ? The specs say 30W max, but anyone have any idea what the typical usage is ?[*]What does the power button actually turn off ?[/list=1]
cheers

[Mike Harrison]

1) Digi cable boxes contain a huge amount of processing power to decompress the video stream. This takes power, most of which ends up as heat. There is also quite a lot of hogh-frequency analogue stuff in the front-end which takes a not-insignificant amount of power The need to build down to a price instead of up to an efficiency spec means they produce more heat than they could theoretically be made to, and don't dissipate it as well as they could.
2) ISTR about 20 watts when I measured one a while ago
3) Almost nothing - just toggles the select line on the TV SCART , turns off the UHF output and the display. Makes negligible difference to power consumption.

[edgerobber]

thanks - I thought that the power button didn't do much.
It seems a bit odd that the box doesn't have a standby mode, but it would probably be a "luxury" they costed out of the design.
I suppose the design to cost thing also explains the size of the boxes.
I wonder if there will be a complete cable tuner/decoder on a chip ?

[spiderplant]

Originally posted by edgerobber
It seems a bit odd that the box doesn't have a standby mode, but it would probably be a "luxury" they costed out of the design.

Not a luxury. The box needs to keep running to keep the EPG data up to date and keep the smartcard active. It means you can use the box immediately after coming out of standby. And it can wake up when reminders go off so you can make recordings. And it can look for software updates. And you can still use broadband. etc...

I suppose the design to cost thing also explains the size of the boxes.

The older models are full of components. And a big box helps with the cooling.

I wonder if there will be a complete cable tuner/decoder on a chip ?

Possibly, but two chips makes more sense. Then the same decoder can also be used in satellite and terrestrial boxes.

well now I'm confused - standby or not to standby

Originally posted by edgerobber
It seems a bit odd that the box doesn't have a standby mode

yet

Originally posted by spiderplant
It means you can use the box immediately after coming out of standby

Make your mind up !

[MikeyB]

I've seen a few posts about boxes getting so hot.

How comes a Sky Digital box doesnt get hot? Must be very similar technology used to decode the pictures. Mine never even gets warm at all.

[zoombini]

How do cable boxes work ?

Intermittently in NTL's case.

Originally posted by zoombini
Intermittently in NTL's case.

Well someone had to say it ... lol

Originally posted by MikeyB
I've seen a few posts about boxes getting so hot.

How comes a Sky Digital box doesnt get hot? Must be very similar technology used to decode the pictures. Mine never even gets warm at all.

The cable box has two demodulators, one for the broadcast pictures etc and one for the return path, then also two modulators one for the RF feed of pictures to your TV, the other for sending back the return path info to the headend.

I think the modulators generate most of the heat.

[darkangel]

I Think that one of ntl's biggest problem is that pace cut corners, didn't specify adequate cooling how much of that is down to ntl I've no idea how many faults are caused by over heating boxes or dodgy eproms the die during updates etc must be quite a high number

[Tristan]

The usual figure quoted is that 1% of boxes die after every software update.

Don't know how many get fried because of overheating though. I wonder if if's possible to open the thing up and add one of those silent PC fans?

[edgerobber]

Originally posted by Tristan
[B I wonder if if's possible to open the thing up and add one of those silent PC fans? [/B]

Methinks Ntl wouldn't be too happy if you did that !!

Originally posted by spiderplant
Not a luxury. The box needs to keep running to keep the EPG data up to date and keep the smartcard active. It means you can use the box immediately after coming out of standby. And it can wake up when reminders go off so you can make recordings. And it can look for software updates. And you can still use broadband. etc...[/B]

I see what you mean, but even then things like the video decompression could be turned off (unless the epg is extracted from that ..) . I think what I really was driving at was that it should be to design a cable box that would use minimal power, while still keeping the basic functions active. For example it could be possible to have just one demodulator active and have it wake up the rest of the box (or even only the necessary parts) when the epg needed updating or smartcard checking etc.
To be honest I don't know, I just like bouncing ideas around.

Does anyone feel like doing some sort of simple schematic of how a box works ?

Plus - if the epg is on my cable box then why is it soooo slow ?

[ppolo99]

Cant they shove a fan in like a PC.

Suppose mabye more problems that may now i think of it.

[Xaccers]

Originally posted by ppolo99
Cant they shove a fan in like a PC.

Suppose mabye more problems that may now i think of it.

bearings go, fan rumbles, causes complaints etc

Now I wonder if you could take one of those huge AGP heat sinks and put it inside...

[kronas]

maybe they should install that huge fan/exhaust system they showed on the new geforce card