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Unit came in with dc offset condition. Started checking supplies. Main rails seemed ok. -16v supply was down to +3. Removed connector from rear preamp output board, unit came out of protect. -16v was now -4. still no output. Disconnected 14 pin connector from front preamp board assy. -16v came back. Started taking resistance measurements. Seemed kind of low at 840 ohms on the -16rail. Found shorted IC (1.3k to gnd) on the rear preamp board and shorted TOL74CN IC on the main preamp front board assy. Changed those out and unit was restored. All IRF class mosfets were ok.