The LAB2104 team restore some good analogue cassette and R2R tape decks. Maybe you know that the pure analog content sounds different than the synthetic digital content. So, you can find some good photos of the construction of the Hitachi D-5500 model on Facebook page of the lab. It is really good machine. The construction is unique. It includes infrared remote control and soft touch control. The problems on this machine were so many. From the beginning the control of the machine does not work. 
The full repair procedure took about 6 weeks. The main part of the components were replaced with new ones. Then the machine was wine tuned. This included the BIAS circuits, also the ATRS test generator. One of the problems was on the waveform of the test generator for the ATRS system. The waveform was square instead of pure sine and it was fixed in electronics. The heads were demagnetized. The tape path was fine checked for problems. One of the problems was on the remote control transmitter. There were many errors in pulse width for different modes. That is why the machine has no control. 
After fine measurement and corrections the control of the machine start to work correctly.
(to be continue…)