Thorens TD-320 MkIII service manual
Looking for a service manual for your Thorens TD-320 MkIII? I'll tell you: it does not exist! But this page does and might help. In short: the TD-320 MkIII is a cross between its predecessor, the TD-320 MkII, and its successor, the TD-2001. So not much surprise there. Get both service manuals and you should be covered. This page should help you understand when the first manual is applicable and when the other one.
Thorens TD-320 family
| Model | Year | Tonearm | Motor | Pulley | Belt |
|---|---|---|---|---|---|
| TD 320 | unknown | TP16 | RSM 50 | smaller | 508 × 5 × 1 mm |
| TD 320 MkII | TP90 | ||||
| TD 320 MkIII | 1991–1998 | RDM 57/12 | larger | 544 × 5 × 1 mm |
Mechanically and visually, all 320s are quite similar. They share the same leaf-spring suspended subchassis concept, common to the whole 3xx series. Main differences between 320s are the tonearm, the motor and the circuit board.
Motor
- TD 320 and TD 320 MkII: Berger Lahr RSM 50, a 16-pole synchronous motor running at 262.5 rpm on 35 Hz.
- TD-320 MkIII: Berger Lahr RDM 57/12, a 24-pole synchronous motor running at 175 rpm on 35 Hz. In theory, 24 poles should give smoother rotation and less motor vibration. This motor was used in many models that came at the same time or after the TD-320 MkIII: TD-318 MkIII, TD-321, TD-325, TD-280, TD-290, TD-295, TD-2001, TD-3001, Ambiance.
Drive electronics
Both motors are driven by the same kind of electronic generator, but the actual boards differ. TD-320 MkIII uses the board described in the TD-2001 service manual.
Pulley
A 24-pole motor turns slower than a 16-pole one at the same drive frequency, so the MkIII needs a larger pulley to reach the same platter speed (about 1.5× the diameter). The pulleys are not interchangeable between MkII and MkIII.
Belt
The greater pulley means longer belt path:
| Thorens type | Circumference | Diameter | Length (laid flat) | Width | Thickness | OEM type |
|---|---|---|---|---|---|---|
| TD 320, TD 320 MkII | 508 mm (20.0") | 162 mm (6.4") | 254 mm (10.0") | 5 mm | 1 mm (or 0,6mm ?) | FBM 20.0 |
| TD 320 MkIII | 544 mm (21.4") | 173 mm (6.8") | 272 mm (10.7") | 5 mm | 1 mm (or 0,6mm ?) | FBM 21.4 |
Vendors describe belts differently: by circumference, length (circumference / 2) or diameter (circumference / π). Length is easiest to measure for an average human being.
You often find belt 6800574 on the Internet, called the "universal Thorens belt". Its actual circumference is about 510 mm, which is way too short for the TD-320 MkIII. You may be able to fit it, but it will stress the motor and the bearings, and it may tend to slip off when changing the speed. Not recommended by any means.
I tested the following belts on my TD-320 MkIII:
- flat belt 173 × 0.6 × 4 mm: works fine.
- flat belt 176 × 0.6 × 5 mm: seems to fit nicely, but slips off.
- flat belt 169 × 0.7 × 5 mm: a little too short.
- Thorens universal belt 6800574 (mentioned above): actual circumference about 510 mm, way too short.
- standard Pro-Ject belt (⌀ 158.9 × 4 × 0.9 mm): way too short.
Manuals
This is where chaos meets confusion:
| Model | Instruction (user) manual | Service manual |
|---|---|---|
| TD 320 | TD 320 instruction manual | TD 316/318/320/321 service manual |
| TD 320 MkII | TD 320 MkII instruction manual | TD 316/318/320/321 service manual applies except for the tonearm |
| TD 320 MkIII | TD 320 MkII instruction manual applies, except for some technical data | TD 2001 service manual applies mostly |