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mab1
Senior Member

Joined: 10/02/2015
Location: United Kingdom
Posts: 263

Posted: 05:51pm 07 Feb 2026

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I'm still on adsl broadband as there's no fibre where i live, but over the last 12 months i've had three instances of the broadband going slow and dropping out - only to find that replacing the line filter cures the problem.

AFAIK the filter is a simple, passive low pass filter to stop the dsl from reaching the phone.

The technical support from my budget phone co. (Pop telecom) is worse than useless, so there's no point asking them (after 4 days, they were unable to identfy a fault, and tried to tell me that 0.09Mbps is normal for my location!

), but i thought the folks here might have some ideas of what to check? The only thing know is that the dc line voltage should be 48v until you pick up the phone, when it drops to 12v.

Also, is there a simple way to test the filters? I'm not sure what's wrong with them that would affect the broadband but not the phone, as it's the phone signal that passes through the filter AFAIK, the dsl goes direct to the rj45 socket.

My only other recourse is to stock up on spare filters

phil99

Guru

Joined: 11/02/2018
Location: Australia
Posts: 2980

Posted: 08:51pm 07 Feb 2026

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Opened one up and found it had 2 inductors in series with the phone outlet and a capacitor across the phone outlet. No markings on them so don't know the values.
ADSL outlet connected directly to the input.

Something that simple should last a century or two. All I can think of is poor soldering or bad socket contacts.

Edit.
Found another that was noticeably heavier than the first so opened it up and it is full of stuff.
On top of the PCB are 7 inductors and 4 capacitors and the bottom is covered in SMDs, including 4 6 pin ICs.

Label: C10 Communications Model No. C10245M
www.c10.com.au
Edited 2026-02-08 07:25 by phil99

mab1
Senior Member

Joined: 10/02/2015
Location: United Kingdom
Posts: 263

Posted: 09:27pm 07 Feb 2026

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phil99 said Opened one up and found it had 2 inductors in series with the phone outlet and a capacitor across the phone outlet. No markings on them so don't know the values.
ADSL outlet connected directly to the input.

Something that simple should last a century or two. All I can think of is poor soldering or bad socket contacts.

I also opened a dead one

- and also found unmarked components, which makes it hard to test them.

Ironically, the phone socket and router used to be in a damp outbuilding until a couple of years ago, and i did have issues with corrosion on the contacts, but never had a filter actually fail; but now it's in the house damp's not a problem. But it's a different socket, router and filters since it came indoors.

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