Expression RFU

My company bought a used Express 24/48 just last year to replace an old Expression.  While doing some spring cleaning I have come across an old ETC RFU.  I am assuming it went with the Expression because it has an old key layout--fewer, slightly different buttons.  I plugged it into the Express because I am desperate for an RFU and I was just hoping.  It did squat.  Does anyone know if it is just not compatible with the newer Express, or should it work and it's broken?

Thanks,
-Tim

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