Today, work was started on a Sansui 881 that will be restored to good reliable working order. This unit has an audible 60hz hum out of the left channel that I suspect is a bad cap or ground. Before getting started I ran a quick test on the power amp to see where the unit stands.
Power output testing was done with both channels driven then with each channel driven individually. Right off the bat the left channel was producing a waveform that was bouncing up and down slowly showing the 60hz hum. A 1Khz sine wave was used for basic testing and the amp was driven to clipping. The right channel produced 70w before clipping the left only 50w. Individually the results was better with the right producing 74w and the left 68w. This receiver does have a few IC’s in the tone section which worries me as they are hard to obtain BA312′s. My original feeling was one of the 10000uf power filter caps was on its way out which are set for replacement anyway.
This unit is getting a good servicing. Power and amp board will have caps, diodes, and transistors changed. I would like to keep the output transistors if possible but will test them as well. Once done I will post a list of transistor substitutions as well.
The amp board is actually removable with a slot on the power supply board and so nice to work on. Here is a few pics of the board out of the unit and many more to come once parts arrive.