The Sony TC-152SD has a complicated power supply consisting of a DC-DC converter module, which generates +24 V, -24 V, +9 V rails from 6 V.
Whether the six volts came from the four 1.5 V batteries, or from the mains transformer, the module has to generate the various voltage rails if the system is to operate. If the module fails, then the unit will not work.
One advantages of a DC-DC converter is that it does not place a great load on the batteries, but instead draws current in very small pulses, prolonging the life of the batteries.
I managed to find another tape recorder with a failed DC-DC converter module and repaired it by creating the same voltage rails using another circuit. You can see these articles in the tape recorder section of the site.
Circuit Diagram of Power Supply
The output from one bridge rectifier feeds around six volts to the DC-DC Converter, while the second bridge rectifier feeds power to the speaker amplifier circuit. The 10 mH and 470 mH coils provide filtering to the power rails based on the oscillator frequency of the DC-DC module.
It is interesting to note that the live and neutral from the mains socket connect directly into the primary windings of the step down transformer; therefore, the transformer isolates the high voltage. Later versions of this model had only two pin sockets, without the earth pin.
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TC-152SD / TC152SD Stereo Cassette-Corder
TC-152SD Audio Board
TC-152SD Cassette Deck
TC-152SD Automatic Stop Issue
Power Supply DC-DC Converter
TC-152SD & TC-153SD Mains Cable
TC-152SD Circuit Diagram
Toshiba TA7122 Preamplifier IC
TC-152SD Features & Images
TC-152SD Audio Connections