How to Fix a Faulty Coax or DSL Line from ISP to Modem

🔧Step-by-Step Fixes

Fix 1: Check Your Modem's Signal Levels

For Cable Internet (Coax):

1. Open a browser and go to 192.168.100.1 (or check your modem's manual)
2. Look for "Signal Levels," "Diagnostics," or "Connection Status"
3. Check these values:
   • Downstream Power: Should be -15 to +15 dBmV (ideal: -7 to +7)
   • Upstream Power: Should be +25 to +52 dBmV (ideal: +35 to +49)
   • SNR (Signal-to-Noise): Should be above 33 dB
4. If values are outside these ranges, you likely have line issues
5. Take screenshots to show your ISP

For DSL:

1. Access your DSL modem's interface (check manual for address)
2. Look for "Line Statistics" or "ADSL Status"
3. Check:
   • Attenuation: Lower is better (under 40 dB is good)
   • SNR Margin: Should be above 6 dB (higher is better)
   • CRC Errors: Should be low or zero
4. High attenuation or low SNR indicates line quality issues

Fix 2: Inspect and Clean Connections

For Coax Cable:

1. Unscrew the coax cable from your modem
2. Inspect the connector:
   • Center wire should be straight and extend slightly beyond threads
   • No corrosion (green/white buildup) on metal parts
   • Outer metal sleeve should be tight, not loose
3. If corroded, clean with isopropyl alcohol and cotton swab
4. If damaged, replace the connector (need a coax crimping tool)
5. Screw connector back on finger-tight, then 1/4 turn with wrench
6. Don't overtighten - can damage the port

For DSL Phone Line:

1. Unplug the phone cable from modem
2. Inspect the RJ11 connector for bent pins or corrosion
3. Check the cable itself for damage, especially near connectors
4. Replace cable if damaged - use shortest quality DSL cable possible
5. Plug directly into the main phone jack (bypass any splitters/extensions)

Fix 3: Remove Unnecessary Splitters and Extensions

For Cable Internet:

1. Trace your coax cable from where it enters your home to your modem
2. Count how many splitters it passes through
3. Each splitter adds 3.5-7 dB of signal loss
4. If possible, run a direct line from the entry point to your modem
5. Or ensure your modem is on the first split (shortest path)
6. Remove any old, unused coax splitters
7. If you must split, use a 2-way splitter rated for 2-3 GHz (not cheap ones)

For DSL:

1. Connect modem to the main phone jack (usually where line enters home)
2. Remove any phone line extensions between wall and modem
3. Bypass any DSL filters if testing (but add them back for phones)
4. Use the shortest, highest-quality phone cable possible

Fix 4: Inspect Outdoor Connections

1. Locate where the cable/phone line enters your home (usually outside wall)
2. Look for:
   • Loose or damaged connectors
   • Exposed/frayed cable due to weather, animals, or age
   • Water damage or corrosion at entry point
   • Cable touching metal (causes interference)
3. Take photos of any damage you find
4. Don't attempt repairs yourself - this is ISP responsibility
5. Contact your ISP and show them the photos

Fix 5: Test with a Direct Connection

1. Temporarily bypass all internal wiring:
   • For cable: Connect modem directly to where cable enters your home
   • For DSL: Connect to the network interface device (NID) outside if accessible
2. Test for 24-48 hours
3. If problems disappear, the issue is your home's internal wiring
4. If problems continue, it's the ISP's external line

Fix 6: Document and Call Your ISP

1. Gather evidence:
   • Screenshots of poor signal levels from modem
   • Notes on when outages occur (weather patterns, times of day)
   • Photos of damaged connections or outdoor issues
2. Call your ISP support and request a "line quality test"
3. Ask specifically about signal levels and line noise
4. Request a technician visit to inspect outdoor connections
5. If first tech doesn't find issues but problems persist, request escalation

ISP is responsible for the line from the street to your home's entry point. Insist they check it thoroughly.