Its hard to see, but I suspect it is just an enclosed SCR drive. If it is, be aware the potentiometer pins will be floating around half mains voltage, so don't go touching any of the pins/wiring when the drive is powered up.

Although due to the dual voltage input, there is a possibility the drive may actually be some kind of SMPS.

If you're desperate to get running again, and want an industrial solution, something like a KBIC ( https://www.axiscontrols.co.uk/produ...eed-controller ) would work, you'd just need to ensure you don't turn the speed control up too high that you over-voltage the motor.
Or you can get a fully enclosed Sprint DC drive for around the same price - https://uk.rs-online.com/web/p/motor...llers/8209558/


Alternatively if you search eBay for "SCR speed controller" there are lots of cheap options, but you'll need to add a fuse to protect for overcurrent.