I dont know why you would expect the HD621 to improve the picture. Its job is to switch between 6 HDMI i/p's and strip the Audio signal for external processing.

The first step if you suspect the HD621 to be affecting the quality of the picture is to bypass it temporarily and assess. If the HD621 is fine, the second thing to check is the HDMI cables.

Like any electronics component, with age things can go wrong/fail. The good news, is that Meridian has a service department, and there are also independents that can service equipment. Of course, this will cost you money and inconvenience having to ship your unit. Hence people here trying to help. If you are confident doing it, checking the PSU output is another thing to check.

Cheers
Greg

M owner since '97