Everyone is allowed two free DTAs but the Rate codes have to manually be added to a persons account when/if they get the boxes. Every account doesn't automatically have the DTA rate codes built in because some people dont need or want the DTAs and every account is different. So if you picked up two or had two mailed to you or even had two installed that doesn't necessarily mean the person who set the order up on Comcast's end built it right. That person may have added the rate code to the wrong outlet or not even added it at all.
This is assuming you have never had two DTAs working and have only always had one working and the second one never activates.
Rate code could be the cause if I understand the issue you are having correctly. For example if someone had a DVD and wanted two DTAs their account should have Video and DVR rates on outlet 1 with the DVR serial number. Then Video and DTA rates on outlet 2 and 3. If they were only present on outlet 2 then the corresponding DTA would activate but the DTA serial number on outlet 3 would not. Wouldn't matter how many DTAs were hooked up in the home or where at in the home if the Rate is missing in the billing system.
Can't guarantee that is your problem but it is something Comcast should be able to check via phone or chat.
usually this only helps a DTA that is already activated and just needs to be reset but......
Try holding down the info button to get into the Diag Screen.Once in there hit 1, 3, 7, 9 on the remote. You should see the screen go out and the DTA reset. Not sure if this will do anything for you but it will reset the DTA and get you to the place where you need a hit (which maybe where you already are) but if you have already confirmed the rate codes are on your account it is worth a try?
Hopefully someone will have a suggestion for my issue, here goes...
I'm on my 3rd DTA that won't activate. I originally received 2 and the first one activated just fine, I waited about a month to try to activate the second one and it wouldn't activate when I tried. I took it back, received a replacement and it wouldn't activate either. I took that one back, received another and it won't activate either. I can take the ones that won't activate to the same outlet as the one that was successful and they still wouldn't activate. I took the last one and connected it directly to cable from Comcast, bypassing any cabling/splitter and it still won't activate. I went into the diagnostic mode and see a signal level of around .9-0 and SNR of 37, which should be more than adequate. The LED flash pattern indicates they are ready for activation.
Have I really received this many bad boxes? I know you will probably suggest sending a tech out to my house, but since I connected directly to my input from Comcast the issue must be upstream form me.