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Have CM400 modem with upload slowdowns that happen at regular intervals
I have a CM400 modem and lately I have experienced a slowdown of only my upload speed starting at a specific time of day between 7:30pm and 8pm for the past week. My upload speed goes from 30mbps bef...
OK I'm at the modem webpage Connection status is 'good'. I am using firmware version V2.01.06 which I believe is the latest comcast applied firmware based on the first link you gave me. Event log is as follows...toms and if there had been a fix for it.
| Mar 21 13:02:19 2026 | Critical (3) | No Ranging Response received - T3 time-out |
| Mar 21 13:04:09 2026 | Critical (3) | SYNC Timing Synchronization failure - Loss of Sync |
| Mar 21 13:04:15 2026 | Warning (5) | Lost MDD Timeout |
| Mar 21 13:04:55 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| Mar 21 13:06:15 2026 | Critical (3) | No Ranging Response received - T3 time-out |
| Mar 21 13:06:30 2026 | Warning (5) | MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1 |
| Mar 21 13:06:32 2026 | Critical (3) | No Ranging Response received - T3 time-out |
| Mar 21 13:07:30 2026 | Warning (5) | Initializing Channel Timeout Expires - Time the CM can perform initial ranging on all upstream channels in the TCS has expired |
| Mar 21 13:07:31 2026 | Warning (5) | TCS Partial Service |
| Mar 21 13:08:00 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| Mar 21 13:33:30 2026 | Critical (3) | No Ranging Response received - T3 time-out |
| Mar 30 21:38:16 2026 | Critical (3) | SYNC Timing Synchronization failure - Loss of Sync |
| Mar 30 21:38:21 2026 | Warning (5) | Lost MDD Timeout |
| Mar 30 21:39:13 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out |
| Mar 30 21:40:23 2026 | Critical (3) | No Ranging Response received - T3 time-out |
| Mar 30 21:40:40 2026 | Warning (5) | MIMO Event MIMO: Stored MIMO=-1 post cfg file MIMO=-1 |
| Mar 30 21:40:42 2026 | Critical (3) | No Ranging Response received - T3 time-out |
Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box.
Be sure your using good quality RG6 coax cable up to the modem.
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/