Visitor

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1 Message

Saturday, May 23rd, 2026

Cable Modem Critical Problems MB 7621

I’m receiving these errors from my event log in Motorola MB 7621 ( 2.5 years old).

Warning (5)   Dynamic Range Window violation 

Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out

Warning (5) DHCP WARNING - Non-critical field invalid in response

Critical (3) No Ranging Response received - T3 time-out

Cables inside are tight. Outside cable and splitter on the pole 21 years old. 

Is this an issue with outside wiring and splitter?

Thanks

Oldest First
Selected Oldest First

Moderator

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365 Messages

1 month ago

Hi,

 

A T3 error indicates the modem lost did not receive a response within 250ms. Many things may cause this. I very well may be the line or splitter outside, but it could be something else.  The first thing I would have recommended is to make sure the coax cable is tight and secure on both ends.  It sounds like you already checked this. If you continue to get the errors, or you notice slow speeds or drops in service, please contact us privately so we can help make sure this gets fixed. Please feel free to email us at cox.help@cox.com. Please be sure to include your name, full street address, and a link to your forum post.


-Greg

Visitor

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72 Messages

1 month ago

What are your upstream power levels? Can you get rid of or replace the splitter? If its old thats where i would start.

Honored Contributor

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2K Messages

FYI I remember using Polaris to get modem levels, LOL

Honored Contributor

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2K Messages

1 month ago

FYI, the MB7621 is NOT a Motorola Modem. Zoom secured an exclusive, multi-year trademark licensing agreement with Motorola Mobility., and slapped the name on their equipment. ARRIS purchased the hardware and software, and that's why Arris is selling SURFBOARD (SB) Modems. 

In 2015 and later extended, the agreement allowed Zoom to brand and sell consumer networking gear (such as cable modems, routers, and MoCA adapters) under the recognized Motorola name. Please note, NAME ONLY, Arris has all the intellectual property. 

https://arris.my.salesforce-sites.com/consumers/articles/knowledge/Motorola-Zoom-ARRIS-Branding-Name 

(edited)

Visitor

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72 Messages

I heard Arris just got bought by someone else. Never heard of company so cant recall name. I dont think SB8200v3 is actually Arris.

Honored Contributor

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2K Messages

@BiPolaris​ Arris was purchased by CommScope in 2019, but everything is intact, all mfg, software and hardware. 

(edited)

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