Have a V7 motorhead serial no TS1 UK KBR3429A, bought May 2018. Main cyclone unit is cleaned out and working OK, but motorhead is still intermittent / pulsing. Basic disassembly and cleaning as per Dyson troubleshooting has not solved the problem. The motor can be turned and runs with the roller removed.
Any further suggestions? I looked at your V6 head maintenance video but this is different, do you have an equivalent for the V7? Also looking up spares on this site, the serial number isn't recognised.