Need help with malfunctioning master control

I bought a house with a nutone im4006 intercom that worked fine. The painter pulled the master control out slightly to paint around it and it now has problems. It has a continuous hum and works sporadically otherwise. The electrician and handyman will not look at it because it's such a specialty item, in their opinion. I'm not sure if the painter pulled a wire(s) or let dust get in the machine. Short of replacing it, what can I do? Some speakers in some rooms work still with radio. I have no paperwork on it. I can't make it any worse. I'd like to try to fix it.

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