From: kaoz0091jm@gmail.com   
      
   Hey Robert, I have the same sort or issue with an awfully load (machine gun   
   like) buzz through one of the channels. I have 2 Rock-ola 480's and believe   
   all around that era used the same amp (478,480,481,483,484). I found with one   
   of the amps if had a    
   mosfet transistor in the heat sink section underneath the driver board. I had   
   +30V or -30V (can't remember) at the speaker out wire . It's supposed to   
   measure about 0.001V when volume at minimum but when one of the transistors   
   failed the balance of +30V    
   against -30V is lost to equal 0V and you get a load buzz. Check Q14 and Q15   
   transistor (one for the - and the other for the +) and replace the faulty one.   
   It could be a transistor on the driver board instead. My other 480 had a very   
   similar loud buzz but    
   problem was on the driver board. Easy way to be sure is just switch the left   
   and right channel driver boards and see if the problem carries with the switch   
   to isolate where the problem is. All my transistors tested OK on the driver   
   board except I can not    
   test the 2 in side the custom PEC-8. I believe my part is faulty and have   
   parts to build the tiny PEC-8 myself but I do not have the values of the   
   diodes or the 2 transistors. Please let me know the numbers on these parts so   
   I can determine the values to    
   build my own. You likely need a magnifying glass as the code numbers are tiny   
   (about 1mm). If your PEC-8 replacement does not work then check your other   
   transistors - they work in sets of 2 like in the heat sink circuit - one for   
   +30v and other for -30V   
      
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