the 1900 engine is difficult to take apart, the red disc that regulates the speed icw the magnets is hard to remove and not replacable. I have restored a lot os 1900 100 and 3400 players an almost always good greasing will sove the problems in case of low speed. The upper bearing can be greased with spraying good quality oil on the axle under the red disc, just a bit, let in stay for a while and let the engine turn and see what happens. The lower bearing? Simply drill a very small hole acentric in the plastic that holds the bearing and inject a little oil in it. Do this only when you dare to do it! Success 80%!
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