5.1 surround rear speakers not working

I'm having trouble with my rear speaker.
I have re-installed my windows 10 and the updated drivers for my onboard audio card.
Set audio channels to 5.1 surround and ran the test.
All speakers are working.

Yet when I run a 5.1 surround test from an external audio source (YouTube) there is no sound coming out of the rear speaker.
In fact the sound that was to be coming out of the rear speaker is actually come out of the front speaker.
The rear speakers are also not working with any other player.

I just can't figure out why I can't get it to work.

Please help

Rob