Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

My cable modem has been pushing the limits of the allowable upstream power levels (getting between 55-58 dBmV). This is causing the modem to reboot. Is there something I can do to reduce the upstream power level? I'm not entirely sure what causes this - could the number of things plugged into that surge protector affect it? Can using a different outlet affect it?

share|improve this question
There is no reason high output power levels should cause a modem to reboot. It sounds like the modem is either overheating (bad positioning?) or defective. – David Schwartz Nov 17 '12 at 15:25
I've had the modem replaced, and it's still happening. I guess overheating is a possibility. I've read that the normal power levels should stay under 58dBmV - what can happen then if I exceed those? – Jeff Storey Nov 19 '12 at 1:54
The modem knows what power levels to use, that's not the issue. How did you determine that the issue is the modem rebooting? – David Schwartz Nov 19 '12 at 2:01
I was watching the modem when it happened. All of the lights on it turned off and the reboot process started. – Jeff Storey Nov 19 '12 at 13:30

This is almost surely due to a wiring problem. The most sensible thing for you to do is to call the cable company to explain that your DOCSIS connection is unreliable and get them to send someone out to troubleshoot it and fix it. If they give you the run-around, mention that you're planning to switch to a competitor of theirs, and see if that helps.

If your downstream levels are decent (above -10dBmV or so), this could be due to a loose connection. Loose connections can sometimes impair low-frequency carriers without impairing higher frequencies very much. Tighten every F-Connector you see.

Inability to communicate upstream shouldn't cause a cable modem to reboot, but it WILL eventually cause it to re-start the sign-on process from scratch, which can take quite some time. When this happens, the blinking pattern of the cable modem's lights will look fairly similar to a fresh boot.

share|improve this answer
Thanks for the detailed reply. I've had the cable company come out twice and both times they said the signal is fine. I'll verify by downstream connections, but I think it's been primarily a problem with upstream. I'll go through all of my connections, tighten them up, replace splitters, etc and see if that helps. – Jeff Storey Nov 28 '12 at 14:47

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.