Unknown part from a running LED light display

[DMartens]

Have an old (1980's) LED display sign, made by Text Lite, model MM300, typically used in shops windows to display promo messages etc.
Modified the unit and replaced the original microcontroller, RAM etc. by an Arduino. All is working fine but it has an unknown component in it that mystifies me and that I would like to identify.
It is 30mmx30mm square and 16 mm high. No text on top. Text on bottom has pin numbers 1 through 10 around the perimeter but only pins 1, 5 and 8 are physically present. It also has the text "29-1" and "bfi". Couldn't find anything on google text search, nor on google image search.

Anyone got any ideas what this is? Pictures of component and MM300 attached.

[capt bullshot]

My guess:

A potted toroidal inductor - not sure what the third pin is, maybe just electrically not connected and used for mechanical stability only.

[Terry Bites]

Could be an evil autotransformer..

[ajb]

What was it connected to in circuit?

These days that's a common form factor for things like DC-DC converter modules, a little plastic box that a PCB etc gets dropped into and then filled with potting compound.  But at that age, you couldn't fit all that much complexity in there just due to the components that were available.  Could be just about anything, but only having three pins limits the options a fair bit.  The potting boxes are generic and can be bought off the shelf, hence ten pin positions with only three loaded.

[StillTrying]

I don't know what it is, it does look like one of these early attempts at a DC-DC converter.

https://www.acalbfi.com/uk/Power-supplies/DC-DC/PCB-mounted/c/CAT-13-03-05

[DMartens]

Thank you all for your replies and sorry for my late response ... initially I also thought it was a DC-DC converter but the number of pins does not seem to make sense as I would expect there to be at least 4: 2 for input and 2 for output ... but the component has only 3 pins populate so a toroidal inductor as suggested by Capt Bullshot is the most likely.