heidelberg windmill press

Have you greased the pulley lately? Grease nipple in centre of pulley hub, just a guess.

It might be the brushes on the motor.

A few basic primitive tests for starters, (including) as Frank implies above, i.e. grease the nipple, General purpose grease quite adequate, initially, ordinary simple pump plunger action is sufficient, High pressure not required, H/bergs normally came with the simple pump/plunger style.!

Next possible step, with the motor off/isolated flip the top of the belt guard, to access the flywheel & belt, with the clutch engaged, with NO forme or chase in and the impression handle IN, it should be quite easy to rotate the flywheel, >clockwise< will rotate the coned pulley and the motor, proving or disproving either the problem is in the M/c. itself or the Motor, armature is the problem OR the coned pulley itself is the cause, i. e. not opening up.

Coned pulley action can be checked, initially, without altering the speed control, without removing the belt,!! by either having access to the rear of the M/c. and with 2 hands attempting to pull the outer Cone OUTWARDS>, just a fraction, You will quickly sense if the full travel is possible, the spring is not that strong and will allow the belt to settle a little further down in.
IF
The above is not practical or possible, it is fairly simple to take a small baulk of timber/lumber 18” long in the order of 2” x 2” taper a point on 2 opposing edges, from 2” x 2” down to 1-1/2” and with a mallet, attempt to push the 2 parts of the cone apart, 2-3 modest taps will verify if the moving cone IS moving, or otherwise.
IF
The coned mechanism appears to be working, next step possibly, inspect the inner surface of the belt, the narrowest part of the taper, = M/c. cycled by hand, and with
mirror, looking for cracks and/or friction marks.

And then under power, by implication double checking IF the *smoking* is from the Motor itself OR from the belt binding in the Cone mechanism.
Generally H/berg., Platens are equipped with 3 Phase motors, (under difficult circumstances a few are equipped with single phase) with a broken single phase supply wire, (usually) if wired properly the starting mechanism would not allow the motor to even begin to turn,! IF it is in fact 3 phase, ( & because the motor supply has to move through a small Arc under speed control)

If one phase wire is broken the motor would/may start and hum, but can produce smoking, BUT would normally be dissed, out of action via the 3 overload trips, normally found in the remote control panel/box.
Overload trips normally seen as oil filled dash pots, in the order of 2-3 amps per pot.

Apologies if the above be irrelevant, but may prompt better info. Mick. 01/10/`18.

Thank you for the great information.