Comcast + SB5101 + Mac = Poo

Mac users on Comcast highspeed connections may want to consider upgrading to Motorola SB5120 modems if their SB5100 or SB5101 modems aren’t performing at full speeds. My Comcast service level is 8mbps, however with the SB5101 providing Internet connection to my G5 iMac and MacBook, I was getting no more than 700kbps average download speeds. Even text pages loaded at glacial speeds. The best download test I ever saw was 1800kbps. Upload speeds were fine, however.

Numerous Comcast tech visits provided no relief. Lines were checked, coax cable and fittings replaced, modems swapped out, etc. Nothing improved the terrible download speeds.

After plenty of research and with a tip from a friend at Apple, I found that the SB5101 cable modem has a different chipset that, due to an incompatibility, aggressively throttles download speeds on certain Mac computers. It’s all pretty technical, but the end result is sub-crappy download speeds for Macs (even brand new systems with all software updates) and super fast download speeds on XP systems.

I did my own research online and found others who had the same SB5101 problem. One guy reported that the newer Motorola SB5120 solved the issue for him, so I gave it a try. Comcast brought a new SB5120 to my place, hooked it up, and within seconds I was recording download speeds of over 10mbps!!! Upload speeds remained high around 650kbps.

Conclusion – upgrading from SB5101 to SB5120 too my speeds from 700kbps to 10mbps. That’s a speed jump of about 15x.

Of course, it took half a dozen aggravating visits from Comcast, hours of down-time, hours of online research, following several wrong leads and then luckily landing on a few blogs… but hey – it works!

As a side note, Comcast phone support and upper level tech support denied the SB5101 incompatibility issue. I called Motorola directly and was told the same thing – that there’s no reason the SB5101 should give slower performance with Mac systems. Two days later, I got a voicemail from Motorola support acknowledging that the SB5101 has known issues with Mac systems. They said the reason is “unknown” but that they’re working on a solution. Easiest solution – dump the SB5101 for the SB5120 and the headaches will go away.

  1. Aww, the mp3 is missing. I kinda wanted to hear that message.

    Anyway, thanks for taking the time to post about your issues. I’ve got an old Motorola surf board and experiencing similar mac slowness. You may have just solved my ongoing problem. Many thanks, Waffen

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