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S34 speeds are slower when plugged directly to PC with ethernet cable than when connected to router

  • August 27, 2025
  • 1 reply
  • 110 views
P
The Many
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I have a brand new S34 modem and am using Xfinity 1.2 gig service. I have never seen download speeds over ~450 - 500mbps and have asked Xfinity support for help. They tried a few things, but the speeds still remain the same.

Of course they said to bypass the router (Asus RT-AX88U) and plug directly into the modem which I did, but then the speeds drop down to ~90mbps both up and down! 

Going back to the router, they jump back up to ~500mbps. I would expect the exact opposite to happen. I am using Ookla speed test site both times. Can anyone offer some advice?  Thanks! 

Best answer by SURFboard Moderator

There is a possibility that your Wi-Fi adapter is capable of achieving higher speeds than your Ethernet port. Please check your Ethernet adapter settings, especially if you're testing the speed through your computer. Also, try swapping the Ethernet cable to rule out any issues with the cable itself.

We recommend checking the cable signal levels within the modem. If the signal levels are out of the acceptable range, they can lead to the kind of slow issues you're experiencing.

When the signal levels are within the recommended range, your modem can maintain a stable, high-quality connection to the internet

Please refer to the link below for instructions on how to check your cable signal levels:

https://arris.my.salesforce-sites.com/consumers/articles/knowledge/S33-Cable-Signal-Levels

If you find that the signal levels are not within the recommended range, we suggest contacting your Internet Service Provider (ISP) to have them reviewed and adjusted as needed.

This topic has been closed for replies.

1 reply

S
Wi-Fi Warriors
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There is a possibility that your Wi-Fi adapter is capable of achieving higher speeds than your Ethernet port. Please check your Ethernet adapter settings, especially if you're testing the speed through your computer. Also, try swapping the Ethernet cable to rule out any issues with the cable itself.

We recommend checking the cable signal levels within the modem. If the signal levels are out of the acceptable range, they can lead to the kind of slow issues you're experiencing.

When the signal levels are within the recommended range, your modem can maintain a stable, high-quality connection to the internet

Please refer to the link below for instructions on how to check your cable signal levels:

https://arris.my.salesforce-sites.com/consumers/articles/knowledge/S33-Cable-Signal-Levels

If you find that the signal levels are not within the recommended range, we suggest contacting your Internet Service Provider (ISP) to have them reviewed and adjusted as needed.

SURFboard Community Moderator Team
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