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Author Topic: ADSL cuts out when phone rings, but ZyXEL router does not resync unless rebooted  (Read 418 times)


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I am helping a friend out with their broadband, I have an idea of the cause already but Iíd just like to see what others thoughts/experiences were.

My friend recently moved into their new house last week and has had the broadband going for nearly a month now. However upon when I set it up all for then I noticed that router would disconnect from the DSLAM intermittently when using the phone, it doesn't always do it. However when it does the router does tries to resync continuously evident by the flashing DSL light but fails, however if the router is rebooted it works again. Not sure why this is, I've not an issue like this. The router is a Zyxel VMG3925-B10B which I recommended for them instead of the rubbish Plusnet router. They are using ADSL2+ which the router also seems to not to like to sync at unless I force it to, seems to prefer ADSL Max instead. They have two master sockets in the house, one is redundant, the other is the one having this issue, and seems to be a recently added new line prior to them moving in.

There is no extensions connected to either master socket, they are using an MK3 faceplate which I recommended, with the router DSL lead in the top and phone the bottom. Their line is quite short circa 855meters including E and D side, and syncing at 23.5mbps around when they first synced, but is now reduced to 19mbps with an attainable of approx 21mbps.

My plan is to remove the MK3, try the Zyxel then in a microfilter in the test socket and see if itís the MK3 socket. If that makes no difference will try the Plusnet router and that doesn't work ring Plusnet and report a fault but as it does not direct effect the phone as the phone works I assume I donít report it as a voice fault? I am right in thinking it could be a loose or bad connected joint, or a HR fault? Their line/neighbours lines in the area where network rearranged a few years ago when they installed fibre in the village so they are now connected to a PCP instead of EO. Have any of you on here had a similar issue with a Zyxel or other brand router that seems to be the oddest to me, where it tries but fails to resync unless rebooted? itís done that few times before.

I Can provide line stats if needed but will have to wait until Monday evening before I go round to look into it further. I have done a quiet line test when I fitted the MK3 and router, I noted a slight humming on the line not very loud. The line can error a lot at times but other times its ok. When it was first connected prior to Plusnet going live it would accumulate around 400 es in 5 mins on the downstream. It got better since it went live but still occasionally go up a lot.



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  • Kitizen
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You can't have two master sockets!

Can you identify which socket the line from outside comes in to? If you can remove the front plate(s) to get to the test socket. Now check if the other socket is dead - if it is not the sockets are incorrectly wired. If you can't see which is the first socket remove everything from both sockets to get to the test sockets and check that only one is live.

If only one socket is live, plug in the router ONLY using a dangly filter and check if the line drops when you call the number using your mobile (you should still get the ringing tone). If that is OK try plugging in a phone and using it.

Report back on what you find and we'll take it from there.
Line rental: Pulse8, Broadband: AAISP Home::1 FTTC 80/20, Mobile: id Mobile


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Hi Jelv

Sorry I should said they are both two separate lines I already check that before they moved in. One line is dead the other is the one with issue and was installed recently prior to them moving in. I will have a play with the microfilter and test socket on Monday. Do you have any ideas on the ZyXEL router not resyncing until rebooted? Bit of an odd one, but annoying for my friend as they have to keep rebooting it, which they didn't know at first as a temporary fix.


  • Kitizen
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Unless it's a 2nd Master Socket for a 2nd line, there's no reason there should be 2 of them.

The Zyxel trying to use a different ADSL modulation is a red herring. Many modems pick the incorrect type when set to Auto.
You should always manually set the XDSL parameters you want.

I'd try the test socket, and if the DSL link is broken when the phone is used again then call the ISP and describe the issue in detail.

I'd also fire up registrars and see if there's anything obvious showing up from the available graphs.

edit: posts crossed, sorry I'm slow at typing, currently one handed.

As for the Zyxel not syncing till rebooting I have no idea. Never come across such behaviour.
« Last Edit: December 08, 2018, 04:00:13 PM by j0hn »
Plusnet FTTC 80/20 -  ECI now Huawei cab
retx low @ 3dB target SNRM
Zyxel VMG1312-B10A bridged with 1508 MTU + Asus RT-AC68U running Asuswrt-Merlin