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Class D Switching Power Amplifiers and Power D/A conversion

Need Help with Rotel Main Amp Board
Need Help with Rotel Main Amp Board
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Old 26th November 2009, 04:50 PM   #1
TMan152 is offline TMan152  United States
diyAudio Member
Join Date: Oct 2009
Default Need Help with Rotel Main Amp Board

I need help with the Main Amp Board in an old Rotel 402 receiver. I have limited knowledge for troubleshooting transistor circuits. The reciever was blowing the main fuse. The problem is not in the rectifier board nor power supply. It would only blow fuses when the + and - 30Vdc was applied to the main amp board. I thought I had narrowed the problem to a shorted power transistor (Q609 SanKen 2SC1444) but after replacement I still have the problem of blowing the fuse (if it is a 2amp AGC). When a 3amp ACG is in place (as recommended by Rotel) it did not blow but unfortunately I saw a 22 ohm resistor (R620) begin to overheat before I turned off the unit.

This is my first POST. I tried to include a PDF schematic of the main amp board for those of you who are more knowledgeable of the transistor electronics but the "size" limitation is making it difficult so it is zipped. I will genuinely appreciate any helpful input.
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File Type: zip RX-402-main amp schem.zip (472.9 KB, 33 views)
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