Hauppauge HVR-2250 questions

I have a Hauppauge 2250 dual channel receiver in a dedicated PC running Windows 7.

This setup is used to watch / record digital ( ATSC / QAM ) channels and all has been well until recently.
Now I can no longer receive one group of local channels ( 8.1 8.2 and 8.3 ). A scan with WinTV 7.2 does
not detect the channel and Windows Media Center says there is no signal for those channels.
There are several interesting facts -
1 ) the channels DID work a few days ago
2 ) I can still get all of the other channels I have been receiving. Only these seem to have vanished !
3) This tuner uses an outside antenna and the coax is split in one place. the other side of the splitter
goes to a Pinnacle USB dongle tuner which CAN & DOES receive the missing 3 channels along
with everything else.

Both of the tuners are using the same antenna through a single splitter and yet only one of
them ( the USB tuner ) can receive this particular group of channels !!

I've even tried swapping the output coaxes at the splitter - still no luck.

Have NO IDEA where to go from here.

Any thought, ideas ???

Thanks in advance