The Thorens TD 150 turntable, released in the mid-1960s, is considered one of the founders of the modern floating chassis concept. Its design is still used in a number of modern models, including the Linn Sondek LP12. This device is simple in design, but requires careful attention when repairing and upgrading. This article compiles key information from technical manuals and user experiences for technicians working with the TD 150.
Electrical diagram and motor
The Thorens TD 150 uses a synchronous motor powered by alternating current. The main motor connection diagram includes a phase-shifting capacitor. This is one of the most important components, ensuring the correct rotation of the motor.
The circuit is quite simple: the mains voltage is supplied to the motor through a switch and a capacitor connected between the two windings. The capacitor is used to create the phase required for a synchronous motor. If it fails, the motor either stops starting or loses power.
The original circuit does not have overvoltage protection, so modern craftsmen often add fuses, mains filters, and soft starters. There are ready-made boards that can be purchased on specialized websites or assembled independently — for example, projects on Audioworkshop.org offer reliable and safe solutions for powering old Thorens turntables.
Tone arm and grounding
The original Thorens TP13A or TP16 tone arm in its early version has four signal wires — left and right channels with their negatives. Most devices do not have a separate grounding wire, which can lead to background noise when connected to a modern amplifier.
When restoring or replacing the tonearm, technicians are advised to add a separate grounding wire running from the metal base of the tonearm to the ground of the preamplifier. This is especially important in conditions of high interference or when using a phono preamplifier with a sensitive input.
The color coding of the signal wires may vary, but the most common are as follows: white and blue for the left channel, red and green for the right channel. When replacing the cable, it is important to observe the phase and avoid cross-connection.
Mechanics and design drawings
One of the features of the TD 150 is its suspension — the sub-chassis is attached to the main plate by three springs that isolate the disc and tonearm from external vibrations. This design requires precise adjustment: adjusting the height, centering, and balance of the springs affects the level and stability of playback.
Craftsmen involved in restoration or modernization will find the diagrams showing the location of the springs, sub-platter mounting points, motor, and tonearm useful. These drawings are contained in the service manuals available on the VinylEngine, ManualsLib, and Elektrotanya websites. There you can also find the dimensions of the support disc, bearing seat, and tonearm mounting diagrams.
The subchassis is usually made of an aluminum plate with holes drilled for the motor and disc axle. The tonearm is attached to a removable panel, which can be replaced with a new one suitable for a modern tonearm, such as Rega or SME. To do this, it is important to use accurate drawings of new tonearm bases, which are published in open sources and discussed on VinylEngine forums.
Practical repair tips
One of the common problems in TD 150 turntables is a dried out or damaged phase shift capacitor. It needs to be replaced with a modern X2-class film component with a voltage of at least 250 V. The capacitor can be soldered directly or installed on a circuit board with a fuse and switch.
Another common task is replacing the drive belt. Its length is approximately 550 mm in circumference. Use only high-quality belts, as a belt that is too stretched or too tight will result in unstable rotation speed.
Technicians should also pay attention to the bearing lubrication. The original oil has long since dried out, and the shaft may rotate with difficulty. It is recommended to use specialized oil for vinyl turntable bearings, such as Thorens Bearing Oil or similar products.
Where to find diagrams and manuals
The original drawings and diagrams for the Thorens TD 150 turntable are available on several platforms:
- ManualsLib has a service manual for the TD 150 AB and MK II, which describes the electrical diagram, dimensions, and suspension design.
- On VinylEngine, you can register for free and download PDF documents, tonearm templates, and assembly diagrams.
- Elektrotanya has a PDF file with a service manual that includes not only diagrams but also photos of the components.
Conclusion
The Thorens TD 150 is one of the few turntables that can operate for decades with minimal maintenance. However, its design requires a careful and precise approach. Technicians must take into account the nuances of electrical, mechanical, and grounding aspects. Using original schematics and modern components not only restores the device but also improves its performance.
If you are restoring a TD 150, be sure to use proven schematics and don’t forget about safety. This turntable is a classic not only because of its age, but also because of the quality of its engineering.