Well its many years later! wow, I finally disassembled the entire spindle motor   
    from my 1541-II that is direct drive, there is a Mitsubishi 3 phase motor   
   controller chip M51784P it is a 36pin chip here is the datasheet   
      
   http://www.datasheetcafe.com/m51784p-datasheet-motor-control-mitsubishi/   
      
   pin 34 says speed control, but it is currently grounded. it shows 1:1 or 1:2   
   not sure what would happen if it was disconnected from ground.   
      
   The 1571 has a hitachi chip HA13432 24pin chip that I cannot translate the   
   Japanese or Chinese to help my life, but it looks like the speed controller is   
   changing the R/C circuit to change the pulse modulation that the chip is   
   referencing to adjust speed.   
      
   https://datasheet.octopart.com/HA13432-Hitachi-datasheet-106076.pdf   
      
   this post from lord cross references connecting but not where on Lemon64   
      
   https://www.lemon64.com/forum/viewtopic.php?t=66390&sid=14068c5de33f2ae59ce6524   
   7ffd2951a   
      
   Now if only I could figure out what pin 9 does on the 1571 Hitachi chip then   
   maybe this can be applied to the 1541-II Mitsubishi chip, I think ultimately   
   this was probably used on 5.25 1.2meg high density floppy drives and that would   
    be used to change    
   the speed from 300 to 360 rpm   
      
   have a look and if anybody can figure this one out, then please let us know.   
   Geez everything else has been figured out, even the PLA and the Vic Clock chip.   
      
   -BBP   
      
   --- SoupGate-Win32 v1.05   
    * Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)