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5.3 Modem Troubleshooting

If your cable modem doesn't seem to be able to find a signal, I would check splitters first, and make sure that any splitter along the line is at least 900MHz rated.

If you suspect that there may be a wiring problem, take your cable modem out to the ground block and hook it up there. If it still acts up, it may be time to call your provider for a service call.

by Raydr See Profile
last modified: 2002-03-18 22:20:57

Make sure that you have the modem through as little splitters as possible. Remember that EVERY device you put inline with the cable modem is another obstacle it has to overcome. The cable modem will only try up to a certain amount (around 60db), and then give up.

Put it on the lowest db leg of the first splitter in your residence, if possible. If it doesn't work then, take it to your ground block and see if it works then. If not, then call your service provider.

Some providers can tell you the signal level that THEY [the head end] are receiving. If it's below a certain point, the system will refuse to acknowledge you.

Also see: Upstream Power too High (>55)

by Raydr See Profile
last modified: 2002-03-18 22:20:12

Make sure that the modem has been activated on your account, and that you've given them the correct MAC address.

Some modems will have two MAC addresses written on it, one is HFC (this is the one you give the cable company), and one is LAN.

Please note that you won't be able to tell if your modem is being rejected by the headend unless you've read the manual and it explains what all the flashing lights mean. Not all cable modems will give you this indication.

by Raydr See Profile
last modified: 2002-03-18 22:20:31

Well, the obvious action is to make sure that all your wiring looks good. Make sure you have your splitters configured properly for cable modem service, and that everything looks like it's in good shape. Read the other modem sections to get your signal levels and troubleshoot from there.

If you call technical support, they generally keep a log of your cable modem status, such as downstream power (signal it's receiving), upstream power (how hard it's working), and upstream and downstream snr (signal to noise ratio).

They can look at this chart and tell you if your modem has always had bad signal or if it's something recent.

If they tell you that the line has too much noise on it, this usually means that the shielding has been damaged on a cable somewhere, or you have a really nasty connection somewhere.

If your modem drops in and out even though all your signal levels are good, then it's most likely a loose connection somewhere or a plant (outside of your house) problem.

Please note that if your cable light never goes out but you lose connectivity, it's most likely something down at the cable company, but CAN be a bad modem, or something wrong with your computer. This is not an RF (signal) issue.

If the cable light DOES go out, then it's an RF issue and you need to start looking at the other troubleshooting sections.

Feedback received on this FAQ entry:
  • Should have inside wiring checked for ingress also. Unshielded TV sets, VCR's, Cable boxes, splitters (Radio Shack), connectors (crimped) and coax cable (damaged or store bought) can cause ingress. Most internet provider's technician has the ability to test for it. Remember, inside wiring is the property owner's responsibly, especially if you performed a self install. Coax cable should at least Quad shielded. You can Google ingress and egress. If ingress is detected you will get slow speeds or connectivity drop offs. If you have connectivity you can check transmit levels, receive levels and signal to noise levels by going to 192.168.100.1

    2010-08-15 17:37:55



by Raydr See Profile
last modified: 2003-01-14 16:37:13

Some modems provide a diagnostics page which will give you this information. If not, the easiest way to get signal levels is to call tech support and just ask for them.

Modems that provide diag pages:
(Click each modem name to get to it's diag page)
NOTE: You may need to disconnect the cable line from your modem in order to access the modem's diag page! Also, your cable provider can DISABLE this page, so if it doesn't work, try another method.
Ambit Cable Modems
Motorola Surfboard Line
RCA DCM Line

Most other modems
(Thanks to hsdcable for inspiring me to create this list.)

If you end up having to call Tech Support, they should be able to provide you with the following information:

Downstream Power
Downstream SNR
Upstream Power
Upstream SNR

Fortunately, a lot of providers offer a tool for the techs to use and check signal levels while they're at a job.

While I cannot give you a link to this, I can show you what it looks like. Click here to see my modem levels.

There is also a program you can use to get your modem levels. It's not user friendly, so unless you are familiar with working with DOS, it may be confusing to you.

There is a post in another FAQ with some help on using this program at:
http://www.dslreports.com/faq/2815 (Thanks to Bobcat for the link.)

You can find this program here:
»homepage.ntlworld.com/robin.d.h.···ocsdiag/
(Thanks to Justin for the link.)

Here is some sample output from running this program on MY cable modem:

DocsDiag v011209 Copyright 2001 Robin Walker rdhw@cam.ac.uk

Toshiba DOCSIS Cable Modem: HW 6.62; SW 1.7.007

Downstream channel ID = 4
Downstream channel frequency = 705000000 Hz
Downstream received signal power = 10.2 dBmV
Upstream channel ID = 2
Upstream channel frequency = 24752000 Hz
QoS max upstream bandwidth = 128000 bps
QoS max downstream bandwidth = 1550000 bps
SigQu: Signal to Noise Ratio = 33.5 dB
Cable modem status = Operational
Upstream transmit signal power = 48.2 dBmV
Date and Time = 2002-02-28,22:16:27.00-04:00
Configuration filename = modemcfg/generic-std.bin


Feedback received on this FAQ entry:
  • For most modems disconnect the cable line and try 192.168.100.1 on the address bar and select status tab and you will see signal levels for the forward and return.

    2012-09-29 12:24:03



by Raydr See Profile edited by ergibbs See Profile
last modified: 2003-04-17 09:05:13

Make sure to read my section on splitters and configure your house accordingly.

There are some cases in which a house is just really huge and a ton of signal is lost before it reaches the outlet. Usually, in a case like this, an amplifier or an active splitter will do the trick.

If your cable line is currently RG59, you should REALLY replace it with RG6.

Feedback received on this FAQ entry:
  • Adding an amplifier to an outlet with a cable modem is often not recommended. The cable co. I work for considers it unacceptable. It's best to make sure the cable modem outlet is fed off the first split. A two-way splitter -- one leg feeding the modem outlet, the other leg feeding signal to the splitter for the TV outlets -- does the job nicely. If an amplifier is needed to boost the signal to the TV outlets, it can be placed between the first and second splitter.

    2007-10-07 10:21:21 (defiant See Profile)



by Raydr See Profile
last modified: 2002-03-18 22:02:11

There are two common things that will cause this:
1.) Be absolutely sure that you are not running your cable modem through any extra splitters, and that you are on the lowest db ports possible. (Read my splitter section on configuring your splitters.)

If you have access to DC Taps, use them, they will most likely fix your problem in this case.

2.) If your upstream line is noisy, your cable modem provider will instruct your cable modem to raise it's upstream power in order to compensate for all the noise on the line. In this case, I suggest you review the Common cause for Fuzzy Pictures on Low Channels (2 through 7) section of my FAQ. It may seem unrelated, but Channel 2 and your cable modem return frequency are very close to each other.

If your upstream power is just "barely" too much, but runs fine, I wouldn't worry about it, but if it's so high that your cable company is threatening to take your kids away, then obviously you need to do something.

Maybe the line running to your cable modem is actually bad? Are you sharing it with a TV? Have a new line run.

Installing an AMP in this case will not fix the upstream power, it will just add another device the modem has to work through.

There ARE two way amps for situations like this. I do not know where you could find one, but I do know that they run in the hundreds of dollars range ($250 to $400).

Good luck with this one.

Note by habu187 See Profile: This is also caused by improper return path padding in amps and LEs or the return path at the node could wrong.

Feedback received on this FAQ entry:
  • Would the amplifier at http://www.amazon.com/PCT-BI-DIRECTIONAL-AMPLIFIER-BOOSTER-PASSIVE/dp/B000F28DP2/ref=pd_sim_e_2 reduce the upstream power level without affecting the downstream power level? Also, could I just install this amplifier right at my cable modem vs. at the box on the side of my house?

    2012-10-18 11:56:17 (bspencer See Profile)

  • You can get 2-way amps fairly cheaply. For instance cablestogo.com sell one for$65 http://www.cablestogo.com/product.asp?cat_id=2402&sku=41033&cm_mmc_o=dyBBTkwCjC2-ae%20zEp%20m-aeCjC1bEw%20-F5kbubwyl%20%26%204BpAkzfBylCjCSviNN

    2008-02-17 10:51:38



by Raydr See Profile
last modified: 2005-05-17 09:56:41

If you're not in a huge house, but are still having upstream power problems, here are a few suggestions from Jer Dog

Ask your service provider to run a separate drop for the cable modem.
Not all cable companies will run more than one drop to your house though. (The company I work for only allows one drop per address, which means that the only reason why there'd be more than one drop to a house is if the house is actually split in two and rented out as separate addresses.)

Run a new RG-11 Drop and/or cable line.
Another excellent suggestion. RG11 is an even thicker cable than RG6, and has much less signal loss. If your drop is over 150 feet, then it's a really good idea to have RG11 running to your house.

Although I personally have never seen any outlets run with RG11 cable, this could be done if you had access to it. If your cable company makes a habit out of using RG11 inside the home, then good for you, but if not, I doubt you could get a technician to do it. RG11 is much harder to work with, weighs a LOT, and is very unflexible.

Please note that to properly crimp an F11 fitting on, you need special strippers and a special crimper, AND a special fitting. I haven't seen any stores which carry any of this stuff.

Use a DC instead of a splitter.
This is a GREAT suggestion. DCs are really a different type of splitter, which when used correctly, can really help in loop systems or in other problematic situations.

I will have be adding a section on DCs shortly.

Feedback received on this FAQ entry:
  • hi i am kenny here i have the steam connection problem.. can u help mi to check the problem please.... thanks.... when i turn on my PC getting to Steam... but it can"t... so please do a check for mi & email ---- ACC: thamkenny20@yahoo.com

    2009-05-20 21:46:08 (thamjiada See Profile)

  • you should add a section in here about upload/ download speeds. The number one complaint that I get about our HSI system is speed, but it's allmost allways due to a crappy router. I run through a speed test at www.speakeasy.net/speedtest for all of my customers, and often times a conection will clock 5-6 mbs through a router and 20+ pluged directly into the modem.

    2009-04-10 21:20:25



by Raydr See Profile edited by ergibbs See Profile
last modified: 2003-04-17 09:06:25