Hi, I bought Hitachi TRK-3D80 W. I bought it damaged to repair. I had hope it's only leaking capacitors or cold soldering joints but no. All boards are intact and clean. Subwoofer plays a kind of "wave" pumping fast in and out (nothing that could damage it as it's in fine condition). I removed all screws, and I disassemble it to the last bit, and I don't see anything unusual. I unplug that speaker and screw all back. Nothing is burned, nothing smells funny. All elements are soldered well. There are not so many expensive elements, and all of it is low voltage. I could measure some voltages if needed. That pumping is heard in main speakers too but in much lower volume. I connected it already to 12V external PSU, and it's still pumping like sonic power toothbrush. This sound is on all sources (tape,radio, line in). What causes that? I would appreciate some help. I will send some more p&v as I used sports camera, so the video has too high FOV. Thanks.
re-read, sounds like bad capicitors in the preamp circuits that you cannot knowas to being bad until you just repalce them