Herkese merhaba. 51 yıldır elektronik mühendisiyim ve daha önce hiç böyle bir şey görmedim. I bought a faulty Sony TC-K81 cassette deck second-hand. The mechanical functions, start-stop, forward, and reverse, work very well. However, when I try to play the tape without one inside, there's no sound, but the VU meters in stereo produce a very nice rhythm, as if there were a tape inside. The device does not have a Rec/Play switch slider on the PCB. Instead, it uses CX174 chips. These specific chips have been replaced. The crystal head cables and potentiometers have been tested and found to be working correctly. The supply voltages are as they should be. The VU meters reset when you stop the device. When you look at the device optically from the front, everything appears normal on the panel. When I tricked the mechanics into thinking there was a cassette inside and pressed "Play," the VU meters started playing stereo sound as if there was a cassette, but of course, there was no sound. The service manual was staring at me, and I was just staring back at it. My brain just shut down.
