Motorola SURFboard SB6121 Cable Modem (SB6121)

I felt compelled to write this to help those who will encounter the problems I faced (and mentioned here). I'm one of the many people who wanted to avoid renting a modem from Comcast and bought this modem based on the stellar reviews, only to find that on the day of installation/activation that it "didn't work". Didn't work meant experiencing the same symptoms that's been mentioned here several times - "modem connects but then resets/power cycles/disconnects itself within a few minutes." This happened to me on the day I activated my Comcast internet. The technician spent 1.5 hours trying to figure it out and ended up loaning me a Comcast modem (Motorola SB5120 DOCSIS2), which came up almost instantly and activated just as fast (go figure). He suggested I return this modem as it was defective, in his opinion. I didn't like this since the probability of this was very small. But I saw what I saw and could not get past the first page of Comcast self activation screen with this modem. Before the web page for self activation could proceed, after typing my account info and phone number, the modem would conveniently lose connection. At one point I did get to the next screen where it was scanning for devices, but the modem cut out thereby hanging the process. The modem was packed up in the box for return to Amazon when I couldn't shake how much this bothered me and by my bad luck. So I came back here and read pretty much every review. What I found was there's several people who experienced the EXACT same symptoms while trying several of the same modem. There were two reviews that stood out. One was from a person who mentioned the Comcast technician moaned when he saw it was this modem, indicating that the technician was aware of difficulties using this modem. The person mentioned that after 70 minutes of trying to get the modem to connect the technician advised him to leave the modem powered on and hooked up for awhile and to try activating later. The person did this and was successful in activating the modem. The other review was from a person who was admirably persistent. His review talks of several attempts to connect and refusal to accept that the modem was defective. He ended up leaving the modem power on and connected overnight so the modem could "download firmware". The next day he was able to activate after two attempts with Comcast self activation process. Lastly, I noticed for me that if I left the modem power on and connected but make no attempt to activate it via Comcast web site, the modem retains connection (via indicator lights) for prolonged periods of time. It only seems to lose connection when I try to activate. Based on this I felt something was broken with Comcast activation process specifically for this modem or perhaps Comcast was intentionally making it difficult to activate this modem to convince customers to rent a "reliable" modem from them. To be honest, it almost worked for me. After sitting there watching the technician agonize trying to get the modem to work, I was tempted to rent the modem and move on with life. So as one last hail Mary attempt, this is what I did:1. Took the modem back out of the box and left the Motorola SB6121 power on and connected to cable outlet overnight just to entertain the possibility that some firmware or info needed to be downloaded to the modem and that for some reason it took a long time to do so.2. The next morning I tried Comcast's self activation process.3. Every time Win7's network icon in the lower right corner of my screen indicated that a internet connection was established (vs. exclamation mark) I immediately opened a IE windows and started the activation process with my account and phone #. The modem still lost connection when I did this but I kept on trying.4. It took me about 4 tries to SUCCEED. Each time I tried, I started back on the account and phone # page. But each time it got further and further in the activation process.Attempt #1: Account/phone # screen -> Retrieving Device Information -> Modem lost connection.Attempt #2: Account/phone # screen -> Retrieving Device Information -> List of devices detected (screen showed my MOTR SB6121 modem and a DTV box both shown as "inactive" -> Modem lost connection. (A thing to note here is that Comcast's activation system could specifically identify this modem. This meant it was in their system and their system was able to communicate with it)Attempt #3: Account/phone # screen -> Retrieving Device Information -> Listing devices detected -> Clicked "Rescan" device (modem)-> Hit "Next" to activate then got to screen where it said "Activating Device - This may take 10 minutes" -> Modem lost connectionAttempt #4: This isn't a real attempt because all I did is leave the web browser in the previous "Activating Device" screen and waited for the modem to re-establish connection again. I stepped away for a few minutes and when I came back I got a screen that stated "Device Activate" (and some other instructions that didn't matter) Hallelujah! Also note, NO phone calls had to be made to Comcast to activate this modem.At this point, this modem which was losing connection all the time before, now had a seemingly rock solid connection!!! I'm using the connection now with this modem as I type this. I've did some basic testing, streamed video, surf the net,etc. NO LOSS OF CONNECTION! I did a speed test and I'm getting 25Mbps down and 3.8Mbps up.Based on my experience so far, it is in my opinion that this modem works and is as good as what the majority of the reviewers here have stated. The problem lies in Comcast's self activation process which is suspicious. What doesn't make sense to me is the fact that modem can hold a solid connection if you didn't attempt to activate and after it's successfully activated. It was only when I tried to go through the self activate process that I saw problems. I can't say much about whether step #1 helped but it can't hurt to try. I mentioned it only to inform people of what exactly I did.I truly hope this helps people. Amazon is top notch. This modem is now doing what it's suppose to do with no issues. I'll come back and update this review in about a month to report if it still holds true. I think it will but we'll see. And lastly, thanks for the people who shared their experiences here. If it weren't for them I would have returned the modem back to Amazon and go through the hassle of finding another modem or giving in and renting one from Comcast. I'm trying to pay it forward with this review.

I was one of the first to get a Motorola SB6120 -- and was very much satisfied with the ease of set-up, the awesome speeds, the functionality, and the workmanship. But, like all electronic gizmos, they tend to crap out after a few years. When my SB6120 started dropping upstream channels, I looked to Motorola once again -- right here at Amazon -- and found the new Motorola SB6121.After checking the specs, I found that the new SB6121 Model has the latest IPV6 technology (higher bandwidth capabilities)that were not available on the SB6120. The newer IPv6 technology allows connection speeds up to 160 Mbps., against the 150 Mbps of the SB6120. IPV6 is not in common usage yet, but it will be pretty soon -- And the SB6121 will be ready with the fastest speeds available!!The new SB6121 is a super-easy set-up, and the connection speeds are fast and steady. Comparing the DOCSIS 3 SB6120 to the newer SB6121 : 1.- The Sb6121 is smaller (height and depth are smaller, width is greater). 2.- The SB6121 runs slightly (average about 5 degrees F) warmer than the SB6120. 3.- Connection speeds, latency, and jitter are better with the SB6121 than the SB6120 -- and WAY faster than ANY DOCSIS 2 modems, regardless of manufacturer.Some tips I learned from using the Motorola DOCSIS 3 Modems with 2 different (D-Link DIR-655 and Netgear WNR3500L) "N"-speed Wireless Routers: The SB6120 runs coolest when mounted to a wall or other vertical surface, and spaced approximately 1/2-inch away from the surface. This allows an adequate air flow that's necessary to keep the Modem cool. Mounted with the wires pointing straight down, the SB6120 runs at about 95 degrees F in a 78 degree room when mounted away from a wall. Temperatures measured with Mastercool Infra-Red Laser Thermocouple Gun (available at Amazon). The new SB6121 is smaller than the SB 6120, and it runs a little bit warmer (98-100 F), even when mounted the same way as the SB6120. I suggest that you mount the new SB6121 1/2" away from the wall as well, but with the wires pointing straight back. Whatever you do, DON'T STACK ANYTHING on ANY Modem or Router !! Both of these devices give off heat and electrical interference, and will perform their best when spaced about 4 feet apart, which keeps the interferences from overlapping and killing the Wireless Router's range. When you get your internet connection going, go to the Motorola Modem's Home Page: Sample snapshot of my SB6121 =Cable ModemStatus Signal Addresses Configuration Logs Open Source HelpThis page provides information about the current upstream and downstream signal status of your Cable Modem.--------------------------------------------------------------------------------Downstream Bonding Channel ValueChannel ID 49 50 57 58Frequency 837000000 Hz 843000000 Hz 861000000 Hz 867000000 HzSignal to Noise Ratio 37 dB 37 dB 38 dB 38 dBDownstream Modulation QAM256 QAM256 QAM256 QAM256Power LevelThe Downstream Power Level reading is a snapshot taken at the time this page was requested. Please Reload/Refresh this Page for a new reading -1 dBmV -1 dBmV -1 dBmV -1 dBmVUpstream Bonding Channel ValueChannel ID 3 1 2Frequency 36100000 Hz 23300000 Hz 29600000 HzRanging Service ID 7425 7425 7425Symbol Rate 5.120 Msym/sec 2.560 Msym/sec 5.120 Msym/secPower Level 45 dBmV 45 dBmV 45 dBmVUpstream Modulation [3] QPSK[3] 64QAM [3] QPSK[2] 16QAM[3] 64QAM [3] QPSK[3] 64QAMRanging Status Success Success SuccessSignal Stats (Codewords) Bonding Channel ValueChannel ID 49 50 57 58Total Unerrored Codewords 1457238562 1457238645 1457237949 1457238150Total Correctable Codewords 17 26 23 27Total Uncorrectable Codewords 1031 937 1682 1468--------------------------------------------------------------------------------Status | Signal | Addresses | Configuration | Logs | Open Source | Help© Copyright 1997-2008It should give a snapshot of the specs for YOUR modem. You will be looking for 4 Downstream channels that read SNR @ 37-38 db and the power levels at around 0 dbmV. Upstream power levels on all 3 bonding channels should read around 45-50 dbmV. A deviation of 5 from any of these figures indicates a problem.If the Modem's signal is solid and constant, but the power level readings are 5 points off in either direction, check your OUTDOOR SPLITTERS or TAPS first, because they tend to crap out when they're exposed to heat for long periods. The operating temperatures for splitters and taps is only 140 degrees F. maximum, and that temperature is easily reached in direct sunlight, even when enclosed. Those of you who live in hot climates may notice that the Modem's downstream power levels drop off 1 or 2 points when the outside temps get up to 110 F or higher. Don't panic !! In case of rapture, dial 1-800-Oh Jesus. ;>) I found the RCA DH24SP High-Bandwidth (5-2400MHz)2-Way Signal Splitter (available at Amazon) to be an excellent handler of the high-speed signals of Cable, Satellite, and HDTV signals. It's a "2-Way" splitter, so the power flows equally in either direction, enabling MUCH higher upload speeds. If you need a TAP for unequal cable lengths, a CommScope SV-DC-6G Digital Tap worked well for me. For strong and clear Wireless range and reception, use only Category 7 (shielded) Ethernet cable (available at Amazon) between your Modem and Router, and between your Router and Main computer.Good Luck !!

Attention ce modem n’est pas compatible avec de nombreux fournisseurs internet au Québec.Mon fournisseur l'affiche sur son site comme étant compatible mais ce n'est pas le cas.Pourtant au téléphone ils ne m'en on fait mention qu'à la suite de trois appels.Je vais tenter de le retourner... à suivre.Par contre le service a la clientèle du vendeur excellent!

My internet provider is requesting the Customer S/N that is supposedly written (on a sticker) on the box. This sticker was scratched off and replaced with 2 other sticker with bar codes that has nothing to do with the Customer S/N, making this modem useless. I’ve tried to contact Arris/Motorola to see if they could help me with the matter and they say that there’s nothing they can do to help (they don’t have a record of their modem’s Customer S/N.Waisted money!

I purchased this modem to use with Teksavvy. It works great and my speeds are the same as what I use to have on Rogers except I don't have to pay $7 per month for rental.This is just a modem, it doesn't have a built-in switch or wireless, which is the way I like it.

Works great with my ASUS RT-AC66U, Zero issues on Teksavvy..... Bios has good info, if you need to trouble shoot signal issues.... simply and easy

Très satisfait