Powertran Amplifier Repairs
Powertran PSI 4001
This wouldn't power up, the capacitors needed replacing; the main ones were leaking and the small 220 µF on the power amp board appear to be under rated at only 63V. The o\p transistors (Motorola MJ15003\4) were found to have no or low gain and had to be replaced. Worked okay after that. The amplifier uses an unusual feedback from the speaker to the first differential transistor and has a regulated +\- 50V to the main amplifier and a regulated 65V to the amplifier driver stages.