NUTONE INTERCOM SYSTEM 3003

I have a 3003 Master station that had been hit by loightning at least 4 times. It was repaired or replaced each time. I have so much money tied up in this unit. It still works as a doorbell but can barely hear the radio at the master staion and to turn it up you get a screeching noise. Can anyone send me the schematics and or which part to replace. I have my house up for sale and seriously need to get it repaired 1 more time as cheaply as possible.
Thanks in advance

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