A Cautionary Tale

[Rik]

There's only one way to fix this. We all buy one BT share, then go to the next BT AGM and disrupt it by asking pointed questions.

[cavillas]

How about we all contact our respective MP's and put these BT problems to them, at the same time contact TV, Radio and Papers to push the point.  Perhaps greater publicity and pressure will eventually have some effect on BT.

[Rik]

I feel that's the kind of action we need to take, Alf. BT think they are untouchable, we need to make them learn they are not.

[Lance]

Maybe we need to have a template letter written for users to download, sign and post?

[Rik]

It had gone through my mind, Lance.

[pctech]

I think the one BT share each is a good idea.

[davej99]

I opened up a V5 and used Google to identify and rule out each and every chip on the board except one, that chip has a paper label marked "589-005-045 ( ARES ROHS )  and under the label the 2Wire Logo is etched onto the chipface

Found THIS SITE helpful. It confirms:
Ares 3001-000485 [ DMT Modem/Framer/Controller]  2Wire  HomePortal ADSL2+

[MisterW]

According to Zyxel their modems don't use VCXO offset, so that would discount it as the source of the problem for the 662H.

They must use some sort of VCO to allow for slight frequency deviations in the signal from the exchange otherwise it would hardy ever synch at all. I suspect it's just that they don't display any offset like the 2700 does.

The failed 2700 has been running on Sis line since Sunday lunch with no apparent problems - at least I've not had an anguished phone call yet....   

What does it show for VCXO on her line ?

[Tacitus]

They must use some sort of VCO to allow for slight frequency deviations in the signal from the exchange otherwise it would hardy ever synch at all. I suspect it's just that they don't display any offset like the 2700 does.
What does it show for VCXO on her line ?

I can only go by what Zyxel tech support told me, but I think you are probably right.

Regarding the 2700 on sis line, I can't tell you at mo but I'll take a look when I go over there at the weekend.  My own 2700 is currently displaying -112.6ppm.  The old one consistently showed -120 together with a warning that something might be wrong.

[Tacitus]

According to ASL24 the 2-wire is STMicroelectronics and the Zyxel P660 series is TrendChip. This rather rules out the chipset.

According to Zyxel the chip in the 662 (and presumably in the others in the P600 range) is an Infineon AR7.  Apparently Infineon bought Texas so they fall under one umbrella.

[kinmel]

I can only go by what Zyxel tech support told me, but I think you are probably right.

Regarding the 2700 on sis line, I can't tell you at mo but I'll take a look when I go over there at the weekend.  My own 2700 is currently displaying -112.6ppm.  The old one consistently showed -120 together with a warning that something might be wrong.

MY V6 2700  shows  VCXO Frequency Offset:    7.8 ppm    

Is that good, or bad.

[Glenn]

This any use? http://www.analogzone.com/nett0626.pdf

[davej99]

According to Zyxel the chip in the 662 (and presumably in the others in the P600 range) is an Infineon AR7.  Apparently Infineon bought Texas so they fall under one umbrella.

Infineon is the Microelectronics spin out of Seimens AG, who had acquired the DSL product range of TI, I think. So I guess Infineon chipsets are descendants of the old AR7. In the case of 2wire it seems to be an in house design, with firmware originally from TriMedia, a Philips IP spin out and later superceded. This proprietary 2-wire design may be fabbed by STM's foundry in Singapore on a basic design rule set like ARM. The only thing I know about Ares, as on the 2 wire chip, is as a design tool for pcbs and as a flat panel maker. It may be a defunct silicon foundry - don't know. Like most current products, system design, firmware, silicon design and silicon foundry are no longer vertically integrated. So all of the bits of chipset info we have make a kind of sense but we have no way of knowing what it really means as bystanders.

Apologies to Mods. We should be having this chat in the networking section. Will leave it here.

[kinmel]

This any use? http://www.analogzone.com/nett0626.pdf

thanks for that, but a bit beyond me     

[Glenn]

Was for me too 

[pctech]

Infineon is the Microelectronics spin out of Seimens AG, who had acquired the DSL product range of TI, I think. So I guess Infineon chipsets are descendants of the old AR7.

You are correct Dave.

[davej99]

MY V6 2700  shows  VCXO Frequency Offset:    7.8 ppm    

Is that good, or bad.

Now this is an arm waving guess; but I think the ADSL signal demondulation requires a local oscilator, which is kept in sync with the transmitter. A voltage is applied to a local crystal to adjust the local oscillator frequency by up to about 200ppm, but far less in normal operation. I read that 100ppm is high suggesting the demodulator is running on the edge. So 7.8 ppm should be OK. No facts were harmed in the making of this BS!

[Tacitus]

........A voltage is applied to a local crystal to adjust the local oscillator frequency by up to about 200ppm, but far less in normal operation. I read that 100ppm is high suggesting the demodulator is running on the edge. So 7.8 ppm should be OK.....

This begins to make some sort of sense.  The problems I was having were mainly when doing a power cycle.  Unplug the mains and powerup again and neither modem would sync.  Well they might eventually - it took 5hrs on one occasion.  At that point when sync had been gained (VCXO -120 so it was probably on the edge) I could do a software reboot and it would resync with no problems.  It was mainly when booting from cold that the problems occurred.

What you say about a voltage being applied to the crystal, suggests the modem was not applying the correct voltage until it had warmed up, possibly combined with a fault at the exchange which meant the target frequency range was too high.  Mind you that argument fails, since it only took minute or so from a cold start to gain sync on sis line, so why should it be any different on mine?

Dunno.      I suspect that unless someone very knowledgeable put both modems on a test bench and used a frequency generator and oscilloscope, we shall never know. 

It could be that both modems have developed a similar fault, in which case I've been very unlucky. However, given the nature of the fault I suspect there has to be something going on at my exchange as well.  Getting BT to check that out, is a forlorn hope and, given the new costs imposed by BT it's not a risk I'm prepared to take.  Given iDNet's current relationship with BT, I doubt they would be willing to push it any further and, given I currently have a working line, I can't altogether say I could blame them.

[Rik]

The interesting thing would be to 'scope the signal at your master socket, Tac. I suspect that's one side of 'normal' while your routers are the other side. If you compared the signals at your house and your sister's, you'd likely see a significant difference, imo.

[davej99]

What you say about a voltage being applied to the crystal, suggests the modem was not applying the correct voltage until it had warmed up, possibly combined with a fault at the exchange which meant the target frequency range was too high.

Look on the applied voltage as fine tuning of the crystal oscillator from its nominal figure to demodulate the signal received. If it has to stretch too far. say well over 100ppm that could indicate a faulty local oscillator and it might fail to lock and so demodulation will fail. But on two modems?

Now I am just speculating here, because I have no sure knowledge of the workings of ADSL; but I wonder if it might indicate a faulty transmitter on your card at the exchange, if both modems showed a high ppm, yet a nominal ppm on other lines.. We really need an expert to help us here because I am well out of my depth; sorry. So please do not let me send you off on a tangent.

[Rik]

I agree with you, Dave, I'd bet that the card is out, but that most modems will still work with it so BT will do nothing.

[Tacitus]

I agree with you, Dave, I'd bet that the card is out, but that most modems will still work with it so BT will do nothing.

I agree too Rik, but the only way to find out would be as you suggest, to 'scope' the signal at the test socket.  Unfortunately there's no way to find out what the VCXO reading is for the Zyxel.

I think davej99 is right on the mark.  The card at the exchange is probably sufficiently off for both my modems to fail and yet be sufficiently near for other modems to work.  Given the variety of modems, chipsets and firmware, this is entirely possible.

It really needs a high level engineer (and I do mean an engineer) on the case, but I think Hell will freeze over before that happens.

[Rik]

And thaw again, Tac.

[Glenn]

On my 2700 it reports a VCXO of  2ppm

[Tacitus]

On my 2700 it reports a VCXO of  2ppm

Which, since mine show, -120 (the 'dud' one) and -112.6 (the current V6) suggests that the theory is broadly correct.  -120 seems to be right on the edge since it prompted the 2700 to post a msg saying something looked wrong.  Current 2700 is not far off at -112.6 but is obviously far enough from the danger zone to enable it to work.

The only way we will get to the bottom of it is as Rik suggests - put a scope on the main socket and see what the readings are.  Alternatively BT could look at what's happening in the exchange and try swapping the card, but we've already ruled that out.....