Varian Turbo-V 301 system fault. S1: Overtime

I have a Varian Turbo-V 301 pump paired with a model 969-9537 controller and it does not come up to speed, eventually displaying S1: Overtime fault.

From a soft start, during the first step, the turbo spins up to a displayed 12 KRPM with a current of 1.3 A, (P=24 W). The spin rate then slows (6-10 KRPM), though current has increased to ~1.6 A (P=33 W), which I understand to be the limit for maximum allowable power (from page 82 of manual 87-900-940-01 (F)).

I recognise that this type of symptom would typically point to a leak, however for this setup is unlikely, and the foreline is maintained in the low to mid 10-3 mbar range throughout (low while turbo is off, mid while it's trying to spin up).

Could this be a known failure mode for this controller? Is there any troubleshooting I can do in the absence of a spare controller?
I would love to hear other opinions or suggestions.

Many thanks!

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