In low volume technical and scientific gear, which usually include photo gear, multi- tap transformers are rather common. They can usally be reconfigured to work with powere sources as found all over the world.
Finding documentation to figure out what the different taps on the transformer do can be a challenge.
I have more than a few times in the past bought 220/240 gear from overseas, even without the manuals for voltage conversion and converted them for my north american usage needs.
I know this is not for everyone, but here is the basic approcach.
I use an autotransformer (hooked to a GFI/RCD power source) to drive the device with the voltage it originally wanted, and measure the outputs going to the circuit board/rectifier section. Then I unhook the secondary termianls, and measure the voltage again.
Look at the leads insulation colours, and try to guess which ones might be center taps.
Look for leads on the primary tied together if coming from a 220/240 market.
They are likely used to put two 100-140V primary windings into series.
Unhook the links on the primary. Make ohm meter reading to figure which leads are part of the same winding, and whch ones are different.
Then figure which ones are at separate ends of a winding, and which ones are likely neighbouring taps separated by only a few turns.
(keep good notes/lots of digicam snaps, as you go.)
Usually the 240/220 conversion is to take a primary OEM connections, wired in series, and modify it to connect it in parallel.
Make educated guess trial connections on the primary, insulate unused leads, put the meter in AC volts mode, and hook it to the secondary leads that you have previously measure the output voltage of.
Slowly wind up the voltage you drive the primary with from the autotransformer, and stop when you get the desired votage on the secondary. Then go and see what voltage you are feeding the primary. If it is your target voltage you are done. If it is some wierd voltage, then other tap connections that look promising from your ohn meter testing results should be trialled.
Finally, once all is re-assembled, adjust the overcurrent fuse; it is likely going to need ot be doubled for a 220 to 120 conversion.
Make note of any shaded pole motors for fans , etc. They may connect upstream of the transformer, and need special treatment. A small voltage step up transformer or surplus autotransfoeras I had, for one project can be added to drive them at 220V etc. if you are on 120V mains. .