TC-152SD Automatic Stop Issue

Automatic Stop Mechanism

The TC-152SD was one of the earliest tape recorders with an automatic stop (auto-stop) facility. This is a vital facility for a product operating on battery power for portable applications; however, it was an over-engineered mechanism.

The basic problem all engineers faced was in finding a mechanical solution to sensing the end of the tape in a cassette, and using that mechanical signal to trigger the auto-stop mechanism. It was very clever, and the equivalent of pressing the stop button.


Crack in the Cogwheel

Capstan and Cogwheel

A common fault with these machines was the development of a crack on the plastic cogwheel around the capstan spindle. Sometimes this wheel remains in place, but becomes free running.

The mechanism uses the inertial force of the capstan to trigger the auto-stop mechanism. When the larger plastic cogwheel behind the capstan engages with the smaller one, the torque does not transfer from the capstan spindle to this wheel, and therefore, the auto-stop mechanism does not work.

The temporary solution to this is to apply a tiny amount of super glue to bind the cogwheel back to the capstan spindle.

End of Tape Sensor

Servomechanism

When the tape reaches the end, the torque load on the winding spool increases, and this increase in torque load provides a signal to the mechanism to trigger the auto-stop mechanism.

The engineers achieved this through the design of a new component known as a servomechanism, which consists of a clutch assembly that divides the motor torque into two components. The first torque component drives the tape-winding spool. When the tape reaches the end, all the torque transfers to the auto-stop mechanism, which causes the plastic cogwheels at the capstan spindle to engage, which then triggers the stop button assembly.

The clutch assembly is the most critical component, because the two slip surfaces govern the ratio in which the torque divides. They together with the pressure plates determine whether the auto-stop mechanism will trigger.

Over the years, the felt type material between the slip surfaces wears out and may influence the operation of this mechanism.

This Article Continues...

Sony Cassette Recorder
TC-152SD / TC152SD Stereo Cassette-Corder
TC-152SD Audio Board
TC-152SD Cassette Deck
Ferrite Head
TC-152SD Automatic Stop Issue
Power Supply DC-DC Converter
TC-152SD & TC-153SD Mains Cable
TC-152SD Specification
TC-152SD Manual
TC-152SD Circuit Diagram
Toshiba TA7122 Preamplifier IC
TC-152SD Features & Images
TC-152SD Audio Connections