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Common causes of DSL troubles inside the home

1. Filters

Filters, filters, filters... Check for missing, defective or incorrectly installed filters. Filters need to be plugged into the jack first and then the phone plugged into the correct port. Filters can cause sync issues if installed backwards. All equipment except the DSL modem that uses the DSL line needs to be filtered. If you need to have a filter at the same jack as the modem, be sure to plug the modem into the correct side of the filter. Sometimes a filtering issue will not be noticeable and work for years on lower speed packages that get a strong enough signal, but then problems will often occur when upgrading to a higher speed package.

These are some of the often overlooked devices that need filters - dish receivers, dialup modems, alarm systems, phones in the garage, basement or outbuildings, outdoor or extension ringers, some types of water meters and some types of secured entry systems also use the phone line. In some instances a splitter install and home run will be needed to provide proper filtering, usually in situations involving alarm systems, water meters and secured entry systems.

2. Infected Computer

At a bare minimum, make sure to regularly update the operating system and perform virus scans on a regular basis. Infected computers can cause a range of problems that are often confused to be DSL problems, slow speeds, high ping times, etc..

Some free programs to try are Ad-Aware and Spybot S&D. These programs can sometimes find items that your regular virus scan doesn't find.


Spybot S&D

3. Firewalls

Some firewalls, ZoneAlarm is a known example, need to be configured properly to prevent problems accessing the internet. To eliminate this as a possible problem depends on if it is a hardware or software firewall. For hardware firewalls, set up the computer to connect directly to the modem. For software firewalls, disable or shut it down temporarily. If the problem goes away, then the firewall is suspect. If your network contains multiple computers, switches, etc.. you either set it up yourself and know what your doing or you better call someone that knows what they are doing.

4. Customer Equipment

Usually routers are the main culprit, due either to improper configuration with the modem, firmware issue or a hardware failure. Common issues are intermittent surf, connection problems and slow throughput. Set up the computer straight to the modem, if it works ok that way, then the router is suspect. Other common problems involving hardware connectivity are defective network cards and patch cables.

Surge protector power strips with phone line ports sometimes cause problems, make sure the DSL modem phone cord is plugged straight to the jack and not through one of these power strips.

Some older 2.4MHz cordless phones can also cause issues with wireless connections. If you have one of these, unplug it and see if the issue goes away. If so, move the phone as far away as possible from the wireless equipment, otherwise try replacing with a newer phone in the GHz range.

Some rare bizarre things in the home or even a neighbors home can affect DSL. Dimmer switches, treadmills, motion detector lights, defective or failing television sets and monitors can potentially cause intermittent problems. These types of problems are usually rare, are difficult to isolate and involve a good amount of head scratching.

5. Defective Modem

You usually receive a modem from your DSL service provider. Like it or not, the modem is ultimately your equipment unless specified otherwise by your provider. Warranties and replacement policies also vary depending on provider and manufacturer. The average lifespan for most DSL modems seems to be around four years. The usual ways to determine if a modem is defective is to try the connection with a different computer, or borrow a modem and see if your problem persists with the borrowed modem.

If you are sure that the modem is defective and under warranty, call your provider for a replacement. If no longer under warranty, they can be purchased at electronic stores such as Best Buy, Circuit City, etc.. otherwise, call your service provider for either a replacement modem or a tech visit.

Note: Most service providers do not provide technical support for modems that they do not sell or provide.

6. Defective Phone Jacks and Patch Cords

With a visual inspection you can usually tell if a jack or patch cord is defective. Check for loose connection and broken pieces. The other thing to look for is black or green stuff on or between the pins that indicates corrosion or a lightning hit. Most defective jacks and cords are found in basements or garages. Unless you live in a house where someone thought it was a good idea to put a jack in the bathroom or outside.

Avoid using flat patch cords if at all possible with your DSL modem. These types of cords are very prone to interference, often very poor quality and can cause many sync issues with DSL.

If you are handy, a multimeter can be used to determine if a cord or jack is defective. If not sure how to do this, contact someone who does know before tearing the wiring apart and causing a bigger problem.

Jacks and cords are cheap and generally easy to replace. If in doubt, change it out. Again, contact someone who knows how to do this if you can't figure it out.

7. Loose wiring connections

These can be difficult to isolate, but the usual culprits are taped splices and wire nuts. Other places to check are jacks, junction blocks and at the Network Interface or protector. Usual symptoms that you might notice during voice calls are static and erratic ringing. Do not use alligator clips for connectors, for some reason I keep finding more of this lately and it makes for a terrible DSL connection.

8. Excessive Inside Wiring

Generally, if you have more than 5 jacks on your DSL line, you could have excessive inside wiring which acts as multiple bridge taps that could possibly degrade your DSL by causing signal loss or reflection. In these situations, a splitter install and home run to the modem is recommended.

9. Poor Quality Inside Wiring

Ideally, you should have a minimum of category 3 grade cable for inside telephone wiring. However, most older and even some newer homes have quad cable originally installed. Quad wiring has four wires, red, green, yellow and black. Even older wiring has three wires, red, green and yellow. Older still is cloth covered wiring. If you have quad wiring or older, jokingly referred to as category 1 cable, can allow interference from outside forces (usually AM radio) to disrupt the DSL circuit.

Worse yet, is when people use other wire types as a substitute. Some of the wire I have seen used is speaker wire, thermostat wire, doorbell wire and among other wacky stuff an electrical extension cord buried to a garage. Usually duct tape and wire nuts accompany such handiwork.

A splitter install and home run normally is the easiest and most cost effective way to take care of these types of issues.

10. Corrosion

Usually these problems are found at jacks, junction blocks, and the Network Interface. However, the problem could be at any point that condensation can build up. Usual symptoms that you might notice during calls are static, hum, crosstalk and erratic ringing. Check your line at the Network Interface to determine if the problem is with your wiring. A multimeter or other test equipment is usually used to help isolate these types of problems. Again, if not sure how to do this, contact someone who does know before tearing the wiring apart and causing a bigger problem.


Thank you to MrFixitCT See Profile, nunya See Profile and Shadow01 See Profile for their help.

By Shortbus28

Feedback received on this FAQ entry:
  • I am a computer tech, it's been a while since I was called out to a DSL problem. Your info was spot on. THanks for the tips and the money it made. :) ROCK ON!!!!!!

    2009-04-09 12:03:20

Expand got feedback?

by 59126125 See Profile edited by lev See Profile
last modified: 2006-08-05 10:54:13