I have just removed an IM-3003 master unit from a customers house as they the same problem of the buzzing in the speakers. I am a technician and found the trouble is in the filter capacitors for the rectifier. The capacitors were blown open and had leaking dielectric dripping down. The leak had happened some time ago as the dielectric was hardened and yellowed with age. I asked the customer if they wanted me to fix the board but they never used the unit. The charm of the unit wore off years ago. I was then asked to remove the master unit. I have it and am going to design an updated replacement board. There are new units available on Ebay that you can swap out the old units with.

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