Rhodes Chroma Polaris

I have a chroma Polaris in pretty good condition. I just replaced the front panels with new ones that I purchased from Paul. Now I am able to use the lower function button and several of the other buttons that did not work at all before. I still have one problem, however. The upper function button does not appear to be working correctly and I am needing some help troubleshooting the cause.

I do not seem to be able to get the unit to go into the diagnostics mode. I can press the upper function button and it will not stay lit. If I tap it repeatedly very quickly occasionally I can get it to light and stay lit. However, when I try to initiate the diagnostic mode the keyboard will freeze up.

I have tested some of the lower function buttons and combinations and and able to get the adjustments mode to work where I can modify voices. That is really satisfying.

I am not an electronics engineer. I am needing help figuring out what to check next. Has anyone seen anything like this? If so what do you suggest?

Thanks!

Opal