DC40 Brushroll Puzzle

[macman]

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Another year, another DC40 ERP with a non-working brushroll... I fixed this same machine back in March and replaced the whole cleaner head: hair build-up had melted the brushroll spindles.
So when it came back in, I assumed probable yoke loom failure. The brushroll spins on start up but stops again in less than a second. Tested the yoke loom for continuity, fine. Measured voltage at the cleaner head socket, fine at 320V DC. Stripped the cleaner head, motor looks OK, it turns freely, and no visible damage to the comm.
 I'd assume brushroll motor failure, but its only 9 months old,  so any suggestions please? Possibly the PCB is failing only when under load, though no signs of burning on it. Would the momentary start up indicate this?
Unfortunately I don't have a spare brushroll motor I can swap in to test, or another DC40 to swap the head with.

[macman]

Update: the brushroll motor was burning out. I found an old DC25 head I'd forgotten I still had, swapped the motor over and it worked fine.
I know these motors are fragile, but that's the first I've seen fail in less than a year.

[MVacs]

A dodgy PCB can cause them to fail prematurely.