Thanks - that explains 90% of the issue. I'll check this out when I next get a chance - probably not before next weekend. If I pull the HDMI cable out of the Sony HDTV, presumably the picture should re-appear on the old Sony fed by the modulator/coax. The only thing I'm still at a loss to understand is why (when the HDTV is plugged in with its HDMI cable) the old Panasonic still shows the HBO programming, while the old Sony doesn't. The HR23 -> component cables -> component/composite converter -> composite cable -> RF modulator -> coax -> splitter in the home-run chain feeds both old TV's. Surely both TV's running off the coax should show the same thing?