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SkydiveArizonaJ's avatar
New Contributor
7 years ago

CM8200 Cable Modem "Upgrade"

I am now on day 10, and second Cox cable modem CM8200 -- and it still does not work!

For years I had a Motorola that gave me consistent 30Mbps (download, 5Mbps upload).  Cox upgraded my modem to this CM8200 a couple of weeks ago and right after power up I would get 70-100Mbps download and 10Mbps upload).  However after 5 minutes or so my download speed slows to less than 1Mbps!!  Upload speeds remain the same.

A Cox technician came out and could find anything wrong so he loaned me a Panasonic modem/router which worked great, and told me to replace the CM8200 (and return the rental unit) which I did.  The second CM8200 is doing the exact same thing and now I am waiting for a second visit from a Cox technician and living with a .19Mbps connection!

The receive activity light on the modem  is BLUE which indicates it's trying to use DOCSYS3.1 while the send light is GREEN which indicates it's using DOCSYS3.0.  I think something in the network is not supporting DOCSYS3.1.

Anyone else experience this and/or have any thoughts on what to do while I wait for Cox's second visit?

8 Replies

  • JeremyG's avatar
    New Contributor

    I am having the exact same problem.  I attempted to upgrade to the Gigabits package and have had the same experience as you.  I get about 2mbps on average now, but If I power cycle the modem. I can get 300mbps for about 10 mins then it is back to 2.  I have had two technicians come out both said there was nothing wrong with my end.  I exchanged the modem but the issue continues.  I have worked with support daily, and today finally was able to speak with tier2 support.  I have a third tech scheduled for this Thursday.   

    What I learned.  docsis3.1 modems operate on  different frequencies than docsis3.0, and if there are not a lot of users on 3.1 it could likely that not many people are having issues because users using docsis3.0 are not seeing any issues.  Making it more difficult for them to troubleshoot and why the tech's are not finding anything when they show up.  Being that docsis3.1 is new to my area "NE Mesa" I am probably the only one having an issue in my neighborhood if everyone else is still utilizing the docsis3.0 modems.  This explains why my upload speeds have not been affected at all, and are normal. 

    I truly feel my issue is related to a low/misconfigured signal specifically for docsis3.1 upstream from my neighborhood, but getting the right support area has been challenging. 

    Update:  After the call yesterday with Tier 2 support I feel like I have found the right path to getting this resolved.  Hopefully after my appt on Thursday I will know more.  

  • ChrisL's avatar
    Former Moderator

    Would it be possible to try testing the speeds without the router attached and see what results you get?

  • Joe_Mill's avatar
    New Contributor

    I'm having the same problem as you described. I reboot and I have good/normal speed, then after 5 minutes it drops dramatically.

    Everything was working fine until I installed the new modem CM8200....Help!!!!!!!!!!!!!!!!!!!!!!!!!!


  • Hi Joe,

    Please run a speed test directly through modem and let us know the upload, download, and ping. What speeds are you subscribed to?

    Thank you,
  • JeremyG's avatar
    New Contributor

    I have the fourth technician scheduled to come out to the house tomorrow.  Hopefully he can find the ingress signal that is killing my modems signal.  I say that because I am on my third 8200 modem the odds of getting three bad modems, has to be pretty low.  

  • JonathanJ's avatar
    Former Moderator

    Please let us know if you have further issues once the technician leaves.

  • JeremyG's avatar
    New Contributor

    Well, the fourth visit was the fix.  The technician said that there was a bad batch of 8200 modems that went out, he replaced mine with a new one he had in the truck making it the 4th modem since the original purchase over a month ago, and now everything is working as it should.  It is nice to have internet again.  

  • DeeJ1's avatar
    Former Moderator

    Hi JeremyG,

    I'm happy to hear your internet is back up and working again. Let us know if you have any other issues.