Might be a stupid question but had a customer asking why their television changes to 50mhz when the HDR input is selected; when their television is 100mhz.

Is this a setting forced by the receiver itself? Is there an option within the HDR to change this?

Bit puzzled here, the numbers presumably should be Hz not mhz. 50hz gives 25 frames per second from an interlaced source and 100Hz doubles the frame rate by interpolation to 50 fps to reduce flicker. May be the frame doubler only works for SD inputs and can't frame double for other than a 576i input. It would be asking a lot to turn a 1920 x 1080 25 fps input into a 1920 x 1080 50fps signal

Sorry, meant Hz, was spec'ing up a computer processor at the same time (mhz)

I would say that most likely is that it can't interpolate an HD signal, as said above.

Perhaps ask the user to use the 'v-format' button to set the HDR to 576i output.

The TV manual will almost certainly say, if you can get the make/model off them.

The TV display shows the details of the incoming signal, which is always 50Hz or 60Hz - the TV may then double it to make it 100Hz or 120Hz, but it will still display it as 50/60Hz because that's what the source is, and what it needs to tell you.