Rockola 483 Loud Buzz

[R Sado]

Hi,

I have a Rockola 483 that just started making a loud buzz sound when turned on, along with the "Speaker Overload" light coming on.

I recapped and reflowed the solder joints on the connections several years back and it has been fine until now.

I purchased a pair of Rockola PEC 52357 modules hoping that this will fix it. Is there anything else I should be looking at?


Thanks,
Robert

[John Myers]

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