Airport time capsule issue - works on Verizon DSL but not on Spectrum internet

Big difference between a cable modem and a DSL modem.

The cable modem "remembers" the first device to which it connects.....which was likely your computer.....and it will "ignore" any other device that is connected unless you reset the modem. So, your first task is to get the modem to "forget" your computer, so it will associate and get acquainted with the Time Capsule.

In addition, as you might imagine, your AirPort Time Capsule was programmed with specific settings to connect to your DSL modem.....and cable requires completely different settings. So, you'll need to reset the AirPort Time Capsule back to factory default settings and then set it up again to get everything working again.

Specifically, here is what you will need to do:

Power off the modem completely by pulling the power cable from the back of the modem or unplugging the power supply from the wall AC jack. Leave the modem powered off for at least 30 minutes to allow it to reset correctly.

Disconnect the Ethernet cable between the modem and the Time Capsule.

Power up the AirPort Time Capsule.....if it is not already on.....and then hold in the reset button on the back of the Time Capsule for 7-8 seconds and release. Allow a full minute for the AirPort Time Capsule to restart to a slow, blinking amber light status.

Then,, power off the AirPort Time Capsule.

After the 30 minute power down of the modem......longer will not hurt.....connect an Ethernet cable from the modem to the WAN "O" port on the Time Capsule.

Power up the modem and let it run for 5 minutes by itself

Power up the Time Capsule and let it run for at least a full minute

Set up the Time Capsule again. You can use the same device name, same wireless name, same password, etc that you used before.

If you have been using Time Machine to back up your Mac, you may need to reset Time Machine as well, to get backups going again.