"AC1750" is not a model number. What is the exact model number of the device ?
Are you sure it's a combo "router/modem" as you have stated ? When I look up a TP Link AC1750, the only thing that comes up is a straight / stand-alone router, not a "router/modem".
If it is just a router then the answer is yes. All stand-alone router are usable on the Comcast system, as long as they are used with an approved cable modem.
I have a TP-Link AC1750 router/modem and I’m switching to comcast internet. Is this device compatible or will I have to buy a new modem or router?
This model appears to support Comcast (if this is your device):
TP-LINK Archer CR700 AC1750 Wireless Dual Band 16x4 DOCSIS 3.0 Cable Modem Router, Up to 680Mbps Mbps Download Data Rates, Certified for Comcast, Time Warner, Cablevision and Bright House
However, the link
https://www.xfinity.com/support/articles/list-of-approved-cable-modems doesn't list that model when showing TP-Link modem/routers.
Maybe an agent can clarify.
I prefer not to assume.