Cable Modem Light Stays On

Obviously I don’t know much about computers. I just got a cable modem and hooked up to a cable. The computer is hooked up to a surge protector, of course, and this modem is connected to the computer (of course). Now, when I shut off the surge protector, the modem lights stay on. The computer must have some sort of battery to keep the clock running. What kind of battery is it? And is that that is keeping my modem lights on?

The cable modem should also have its own power supply. If you didn’t install it yourself perhaps the cable guy that did pluged it into the wall and not the surge protector.

Your modem might be picking up some DC off the TV cable.

Your computer has a little battery which maintains power to a clock chip. Like a digital watch battery, it lasts for years.

The modem is connected to the computer and not the wall outlet. I did not do it myself, but I can see that’s the way it is connected.

Your modem is powered via voltage from the cable itself.

Thats strange, the Toshiba PCX1000 cable modem I am useing takes external power from a “wall wart” type transformer.
When the AC power goes off the modem dies.
I bet that if barbitu8 looked hard they would find the modems power supply pluged into another outlet and not the surge protector.


Each local area broadcast systems work differently. Some supply power via cable and some use an external CPU for the modems. It all depends on your local cable company and the type of modem.

from this post-

-I was under the impression that the modem did not have an external power supply. (He killed the power to all his devices but the modem is still on! Obviously it would still be on, if not plugged into the surge protector)

I would need to see the actual setup of this system to say for sure.

“Jesus Christ, you have the modem hooked to the printer serial port …Hello! What’s with this Tesla coil in the closet?”

I have a cable modem. It is powered through a power cord (damn wall wart), not the computer. The lights on it stay on after I have shut down the computer. Hope this helps.


P.S. Get yourself a good firewall. Cable modems are a constant connection.

Easy. Unplug serial cable from modem, is it still on?

Sometimes they use that extra power connector in the back of the computer (how many of you forgot its there?) which used to output only enough voltage for a crummy mono monitor, but now put out full voltage. If the modem is using that, unplug it & see if it goes off.

DO NOT plug the modem serial cable back in when the computer is on. There is voltage there, but you can unplug it when its on.

My cable modem is connected to the computer via a network card. I don’t think you can get power from a nic. Maybe there are cable modems that connect via a serial port but I wouldn’t think that they would want to have the UART speed limitation. If the cable modem doesn’t have its own power source I think the power must be comming from the cable itself. Handy’s suggestion of unplugging connections to see what causes the power supply to go away is a good one though.

A network card was installed and the modem is connected to that. There’s a cable, of course, into the modem. There is also an electrical cord from the modem (which should furnish its power) but it is connected to the surge protector. The guy who installed it said that the modem should always be on. I informed him that I shut off the surge protector after I shut down the computer. He said that maybe I should connect it to a different source. I didn’t, but the modem stays on anyway. I haven’t tried disconnecting anything yet, as I’m obviously on line.

OK, I’m back. I disconnected the cord from the modem to the surge protector, and the modem lights went out. Now, explain to me how the modem is getting power from that cord which is connected to a surge protector which has been shut off.

WAG - some of the sockets on the surge protector aren’t switched. What happens if you plug something else into the socket that the cable modem is currently plugged into? Does it continue to get power even with the surge protector off?

Another WAG - Your surge protector is hosed. Get a new one.

I’m back in my office now. By the way, I know there’s a link somewhere in the caption of SD where all the abbrev. you guys used are located, but I can’t locate the site. What do I click on for the abbrev. I see WAG quite often, but don’t remember what it stands for.

Anyway, it’s a new surge protector and it works because I have to shut it off to shut off the speakers. If I don’t shut it off, the green lights on the speakers stay on. When I get home tonight, I’ll try plugging something else in it.

OK, I came home and tried another appliance in the surge protector outlet I use for the modem. With the protector off, the appliance worked. But I know the surge protector is good because it shuts off my speakers. Why would some of the outlets not be switched?

WAG = Wild Assed Guess

I’d say you have proven through experimentation that at least one of the sockets is not switched. This could be by design or it could be due to malfunction. One reason that it might be nice to have a surge protector that has some unswitched sockets is say you want to have a lamp and all your computer stuff plugged into the same surge strip. You want to be able to turn all of your computer stuff off with the one switch but you don’t want to sit in a dark room.

If I were you I would make sure that the socket in question is supposed to be unswitched. If not replace the thing. Then I would make sure that just because it isn’t switched it is still on the surge protection circuit. If not replace it, or make sure everything connected to your computer is surge protected. I’m assuming that this really is a surge protector and not just a power strip. If you don’t have any documentation on the thing and it doesn’t have any answers written on it, I’d play it safe and buy a new one. They are cheap, especially compared to any one piece of your computer hardware.

You might want to use a non-switched outlet to avoid turning off your printer or computer accidentally. Both of them go through a power-down sequence, and simply removing all power cirumvents this and can cause problems, just like a power failure.

id get a new power strip if any of the outlets have voltage. Those things don’t last forever.

When in doubt, read the directions. You cued me in to referring to my user guide for the “Surge Arrest.” I quote from item no. 4: “Two Always On Outlets. These two outlets provide conditioned power directly from the utility source. It is recommended that they be used for charging equipment or for devices that require constant power.”

Luckily, the only one I use now is the one for the modem. I guess if I could just read I wouldn’t have bothered you guys, but thanks a lot.

Mystery solved.