Mastermix 130 mixer switches off after about 30 seconds?

I have a Mastermix 130 mixer that switches off after about 30 seconds of use.

I suspect that this may be the NVR switch rather than the On/Off switch but would be grateful if someone could clarify this before purchasing a replacement.

I have used the mixer on a shorter mains lead as has been mentioned in an earlier question but the issue is still the same.