[julie_m]

The Uher motor is a three-phase design. It's "not quite brushless", in that it does actually use brushes for positon feedback, but the actual heavy current is being switched by transistors; the brushes are switching only small currents, so there is no risk of arcing causing interference.

If one or more phase is not being driven properly, then this is equivalent to a petrol engine not firing on all cylinders. The motor might be able to run fine on reduced power, but not accelerate from rest against friction. Can you get an oscilloscope on the motor windings? It should be obvious which is the odd one.

I did find a wiring diagram for the 4000 Report L online, but that was two computers ago. I do remember the German word schaltplan being in the title, and it was one huge .gif (if my memory serves me correctly, which it doesn't always) image, so a search for Uher 4000 schaltplan may prove fruitful. The later stereo and 3-head Uher machines use the same motor, so even if you can't find the diagram for exact model, the circuitry should be similar -- though newer transistors may have been substituted, and resistor values changed.

Good luck with it! These really are lovely little machines when they are going. Earlier attempts to build portable tape recorders had usually involved compromises such as having to lace the tape differently for recording or listening; having no playback facility at all; requiring bulk-erased tape; no or unclear recording level indication; hand-cranked rewind; no fast forward; non-standard spool sizes and even (boo! hiss!) no capstan drive. The Uher 4000 Report was just a proper tape recorder that was portable.