Comcast is just about ready to flip the switch on upgrades to its network in Chicago, but thousands of area customers could be left without HD service if they are still using older set-top cable boxes.

According to the Chicago Tribune, Comcast began alerting affected customers in the fall of the need to trade in their old boxes for new ones that will work properly on the network. However, the notices did not provide customers with any specific deadline.

Which is a bit of a problem now because Comcast could turn on the upgraded network as soon as… today, leaving those people who haven’t switched their boxes without the service they pay for.

The company downplays the scope of the issue by noting that most people have made the switch while acknowledging that there are “only” a “few thousand left” who have not.

Customers in Chicago who need to switch out their old set-top boxes can get self-install kits from Comcast either by mail or by going to a Comcast retail location. But if you need to have someone come out and do the install for you, that’ll be $50.

The model numbers for the outdated boxes are: DCH3416, DCT6200, DCH3200, DCT6412, DCT3416, DCT6416, DCH6416, DCT5100, DCH6200, DCT3412 and DCT6208. If you’re not sure, the Tribune says you go to channel 1995 and follow the instructions there to see if your existing box is compatible.

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