Sunday, July 1, 2012

Motorola SB6121 SURFboard Cable Modem Problems

motorola sb6121 surfboard cable modemMotorola SB6121 SURFboard DOCSIS 3.0 Cable Modem is generally considered a good choice for replacing the modem that you lease from your Internet Service Provider (Comcast, Charter, TimeWarner Roadrunner, Cox, ...). Here at, we always do our due diligence by looking for any serious issues with the modem. We also offer some solutions and alternatives for this modem.

Here's a summary of the problems that we found with the SB6121 cable modem in our detailed research. These problems were seen by actual customers of the modem -

  • Motorola Surfboard SB6121 keeps resetting / rebooting every couple of minutes, hence unable to register the modem with Comcast. 
  • The SB6121 doesn't tolerate signal issues (noise, weak signal) as much as the older ones like SB6120. 
  • Takes a long time (more than 10 minutes) to establish a link with Comcast, after powering up the modem. 
  • Download speed is too low - around 100kbps even for a 15Mbps service from Comcast.
  • Random disconnections occur every few days.
  • Unable to self-install the modem with Comcast, even a Comcast technician was unable to install it.
  • Worked for couple of months, then just died.
  • Modem unable to receive signal from Comcast, confirmed by technician.

  • Download speed gradually reduces over time, until you reboot the modem.
  • The SB6121 cable modem overheats.
  • Need to keep a ping running in order to maintain connection.
  • Although runs at higher upload/download speeds, the connection wasn't stable.
  • Connects to Comcast fine, but disconnects when a router is connected to this Cable modem.
  • Dead on Arrival (DOA). The modem kept power cycling by itself for no reason.
  • The modem remains in a constant loop of self-test, with all LEDs cycling.
  • Modem connects to Comcast, but loses it's IP address every few minutes.
  • Modem doesn't seem to be fully compatible with Comcast, although it's listed as an approved DOCSIS 3.0 device.
  • No password option available, hence not secure.
  • SB6121 may not yet be supported for Comcast Business Class service.
  • Motorola doesn't seem too willing to honor their warranty, blaming the problems on the Service Providers like Comcast.
Based on the long list of problems seen by other customers of this modem, thinks that it's quite risky to buy a Motorola SB6121 SURFboard Cable Modem, as it doesn't seem to be of a good build-quality, as they call it in the industry. You too may face one of the problems mentioned above, and may have to return the modem.

Solutions / Workarounds that worked for some SB6121 customers

Many of the issues with the SB6121 modem are due to overheating of the device. Here are some solutions that worked for some customers to avoid the overheating issue.
  • Keep the SB6121 in a well-ventilated area. Keep it away from other electronic devices that may generate heat. For example, do not place it on top or near a PC or router that gets warm. Do not keep it in an area that gets hit by direct sunlight. Place it on top of a table, but not inside a shelf.
  • Blow a clip-on fan onto the modem to cool it down. Lower speed setting of the fan should be fine. Even this setting would generate some noise though...

Alternatives for Motorola SB6121 SURFboard Cable Modem

Here's what other customers purchased, after returning their SB6121 modems. The customers didn't seem to face any issues with these modems, and their connections were stable.
  • Motorola SB6120, the previous model. Surprisingly, the previous model seems to be of a better quality than the SB6121.
  • Linksys by Cisco DPC3008. You pay a few dollars more, but gain the Cisco quality and peace of mind that comes with it.
  • Arris WBM760A. This model has been Comcast OEM for a while.
  • Motorola SB5101U. This is DOCSIS 2.0 technology, upto 38 Mbps max download speed, and is considered extremely reliable.
  • uBee DDM3513.