Comcast Internet Repair

Comcast internet service is an excellent value. Yet, the Comcast (HFC) hybrid fiber-coax network is complex. Follow us as we guide you from ordering the proper service, modem settings, your building coax plant, to finally outside coax transmission lines and fiber node issues

When your lights flicker or go dark, you check your neighbor's house for power...

This simple test let's you know if it's a house circuit breaker or something bigger on the power utility pole.

Comcast Internet outages work the same way. Most Comcast outages are not due to that black box in your closet called a Comcast modem. The outages are due to equipment "on the pole". Introduce us to your business neighbors so we may monitor multiple devices on the same street. Then, when your Internet flickers or goes dark, we can report the outage efficiently and thus your neighborhood gets fixed!

How do we do this, We built special software to monitor Comcast by analyzing your cable modem and the cable modems of business sites closest to you.

Comcast problems are usually neighborhood specific. Many times a defect in the main line or an issue with the hybrid fiber/coax node (a green box down the street with a Dominion power meter) is the culprit.

We offer this as a service and it includes submissions of trouble reports to Comcast in your business name and that of your neighbors as well as follow up.

Use Business Grade Internet Service

Modem Performance Issues

comcast repair

Your Building Coax Cabling Must be Perfect

Verify Signal Quality Levels in Your Cable Modem Diagnostic Page

Comcast service delivery is like municipal water service delivery. It's a system of interconnected large and small diameter pipes. Comcast states that a working "water pressure" range is -15db to +15db with lower than -11db as being in the "yellow range". Unofficially, Comcast insiders state it should be at 0db for best performance. The picture below shows a Comcast SMC8014 cable modem diagnostic page with very low downstream power but acceptable (SNR) signal to noise ratio.

Good SNR is especially important if the downstream power cannot be improved. Inside cabling defects such as a loose connection to a TV can cause poor SNR. On critical or new cable modem installs, we will discourage connection of cable TV until performance is proven. It is the customer's responsibility to correct any deficiencies on interior cabling.

You can't measure upstream SNR but you can extrapolate it by the upstream power the Comcast CMTS (head-end) commands the modem to transmit to push the signal back to Comcast.

This is the View from Your Cable Modem Diagnostic Web Page:

comcast repair graph

Verify Signals with Comcast: (This Gets a Trouble Report Made)


Above modem performance must be within normal bounds for a week according to Comcast Scout or Grandslam systems.

Typical Scout Report health Check Report:

These reports show data marked as green, yellow or red. This report is all green.

IP Address of Modem
Current CMTS Status ACTIVE
Current Firmware
Device Make/Model SMC Networks SMCD3G-CCR
Device Up Time 104 days 9:14:35.05
Docsis Capability DOCSIS 3.0
Downstream Signal Quality (SNR) 35.0
Modem Lost Syncs 1
Modem Resets 5
Receive Power Level (downstream) 0.1 Dbmv
Receive Power Level (upstream) 2.8 Dbmv
Serial Number of the Device H29421C3C4
Transmit Power Level (upstream) 48.0 Dbmv
Upstream Signal Quality (SNR) 32.0
Current Device Status  6(Online)
End of Life Status No
Modem Boot File
Your signal quality goal....
Item Minimum specs Best we have seen
Down Power in >= 0 db 0 db
Down Signal-to-noise (SNR) > 32 db > 37 db
Up Power < 42 db < 35.5

Check Event Logs


Errors over 7 days should be within the range below. Errors T2 and up reset the modem. Not good!

T Timeout Error Description / Resolution Acceptable Range
T3 Noise outages frequently occur node-wide and while some may self-clear, many continue until a Plant Maintenence Technician locates and repairs the offending source of noise.  
T4 Service outages or maintenance activity, impairment in the downstream, major faults like damaged drops, or mainline suckouts.T4 timeouts can become commonplace when node capacity approaches 90% due to TDMA(Time Domain Multiple Access) transmit opportunities simply being unavailable.  
T6 DOCSIS configuration file is corrupt, reload  

Ground the Cable per National Electrical Code Section 800-33


Ungrounded Box

Above picture shows a Comcast Box that has NOT been grounded. Arrows indicate where grounded connection should be.

Mainline Tap Problems

two position mainline tap plate


Pictured above is a cable mainline connected to a mainline coax amplifier and to the right a two position mainline tap plate. Two RG-6 coax drops come off the tap plate. One has a blue tag and the other has a yellow tagged HBO channel filter.

In this picture, installing a new (third) connection for a new customer would require the independent installer to first call the cable company to convert the two (2) position tap plate to a four (4) position tap plate, then the installer would need to make a second trip.

Or, to get his "paid per the job" install done, the installer may install a 2-way indoor splitter and then call the office to get the main line tap plate changed.  On the later scenario, the customer who gets split, may be forced into a marginal power level condition. Plus, they will have two unexpected service interruptions. Once the single available connection is split, the second when the tap plate is properly converted to a 4 tap plate and then the new connection dedicated to it's own tap. They may also have marginal power levels and thus marginal service in between splits.

underground two position mainline tap plate

Cap Unused Taps - Check cable

Pictured above is a four position mainline tap with one unused position properly capped to prevent RF intrusion.

Orange RG-6 direct burial cable must be used for below ground installs. The cable may turn yellow with age and exposure to the sun's UV rays. Check the cable for cuts to the plastic sheath.

Cable Fiber Node Problems

Your copper coax at some point meets a "fiber node" that converts the coax electrical signal into a beam of light for transport back to the cable company. A fiber node feeds from 25 to as many as 300 homes and/or businesses. Pictured below is a ground node and then an aerial node.





Within feet of the fiber nodes is a green battery box fed by a power company AC power meter. If the power goes out, the cable node will fail 8-12 hours later when the batteries drain. We hear customers ponder why Internet stays up when their building generator kicks in and then fails later. This is why. After hurricanes, you will see generators chained to telephone poles to power fiber nodes.   

Node Power Problems

We hear customers ponder why Internet stays up when their building generator kicks in and then hours later it fails.

Within feet of the fiber nodes is a green battery box fed by a power company AC power meter. If the power goes out, the cable node will fail 8-12 hours later when the batteries drain.

After hurricanes, you will see generators chained to telephone poles to re-power dead fiber nodes.

This is a one of several reasons why Verizon selected a passive optical fiber product. It has no powered electronics in distribution cabinets that are analogous to the coax fiber nodes. You could say FIOS does it all with mirrors and it does!

Neighborhood Fiber Node Watch

So, one bad node ruins the cable neighborhood!

We test for problems at these nodes by testing the coaxial customers served by the same node.  In short, we monitor you by monitoring both you and your neighbor's Internet connectivity. Our software tracks and correlates connection problems for users of a common fiber node.

Refer Us to your Neighbors

Thus, referrals to your neighbors are the #1 thing you can do to help monitor Comcast quality issues. When we see simultaneous issues from 3 or more otherwise healthy Comcast subscribers on the same node, we can submit an engineering ticket to Comcast to check the fiber node and the mainline for issues.