Casio MG-510 midi guitar indicator light

Many years ago I purchased a Casio MG-510 midi guitar and paired it with a Taurus amp and Siel EK600 expander.  It played beautifully until I put it aside.  I have since picked it up and found that the expander quit.  I bought a used roland GR-20 synthesizer to replace the Siel.  Unfortunately, when I hooked it up the midi indicator on the guitar does not go on (fed by either a 9V adaptor or 9 volts of batteries). 
Is there any simple fix that I can check or do, or a more complicated fix that I can bring to a shop?
Thank you for your help.  

Regards,
Ron P 
Pocono Mountains