Visitor

 • 

7 Messages

09/15/2026 3:07 PM

Power Levels Causing Random Modem Hard Lockups - DOCSIS 3.1 DRW Violation

Hello,

I am experiencing random hard lockups with my Arris S34 modem (3-4 times over the past week). A physical power cycle temporarily restores service.

I checked my signal levels, and the physical line appears to be delivering an out-of-spec signal, causing a DOCSIS 3.1 Dynamic Range Window violation:

  • Downstream Power: Coming in very hot, ranging from +5.7 dBmV to +8.8 dBmV across 32 SC-QAM channels. SNR is excellent (40.9 to 44.6 dB) with 0 uncorrectables, meaning the line is clean but too loud.

  • Upstream SC-QAM Power: Sitting around 36.8 to 37.0 dBmV across 4 channels.

  • Upstream OFDMA Power: Channel 41 is bottoming out at 28.8 dBmV.

Because the downstream is coming in so hot, my modem is barely transmitting. This creates an 8.2 dB spread between my SC-QAM and OFDMA channels, which violates the 6 dB Dynamic Range Window.

Right before the modem hard-locks, my event logs consistently show:

  • Warning - RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW

  • Warning - REG-RSP-MP Mismatch Between Calculated Value for P1.6hi Compared to CCAP Provided Value

  • Warning - Lost MDD Timeout

  • Multiple CM-STATUS event codes 2 and 5 indicating dropped channels.

I am requesting a line technician to check the tap and balance the line (or install an appropriate pad/attenuator), as the continuous DRW violations appear to be crashing the modem's firmware.

Thank you!

Oldest First
Selected Oldest First

Official Employee

 • 

3.3K Messages

6 hours ago

@papow Hello! Thank you for reaching out to us here on the Xfinity Forum. We'll be happy to take a closer look at the signal we're sending you to see what is going on. Please send a Direct Message with your full name and address.

To send a Direct Message: 

  • Click "Sign In" if necessary  
  • Click the "Direct Messaging” icon (upper right corner of this page)  
  • Click the "Start new conversation" (pencil and paper) icon  
  • Type "Xfinity Support" in the "To" line and select "Xfinity Support" from the drop-down list  
  • Type your message in the text area near the bottom of the window  
  • Press Enter to send your message 

How To: Direct messaging within the forum 

[Edited to remove Modmail instructions and add the Direct Messaging instructions]

(edited)

Expert

 • 

121.2K Messages

6 hours ago

@papow @XfinityBenjaminM 

This is not the Reddit Platform. These are the Comcast Community Help Forums. To send the requested information in a private message via this platform;


  • Click "Sign In" if that prompt is visible

 
  • Click the "Direct Messaging" icon  [Edited to remove link to Direct Messaging]

  
  • Click the "New message" (pencil and paper) icon

  
• The "To:" line prompts you to "Type the name of a person but don't do that.

      Instead, type Xfinity Support there. As you are typing a drop-down list appears.

  • Select "Xfinity Support" from the list. An "Xfinity Support" graphic replaces the "To:" line.

  • Type your message in the text area near the bottom of the window

  • Press Enter or tap the > icon to send it

[Permission from and credit given to BruceW].

(edited)

forum icon

New to the Community?

Start Here