Chinon FB-354 spindle motor mostly doesn't start to spin

[8362r8]

Hello out there


I'm still in the floppy biz and try to bring as many of the Chinon's back to life...


With this one (FB-354, Rev.A) all the basic steps are done:
- cleaning heads
- cleaning mechanically
- re-lubricating threaded shaft, guide rail and some other parts
- replaced the 4 elcaps
- cleaning both microswitches



So far, it would runs smoothly if ... the spindle motor starts. Mostly it doesn't start to spin. The ready signal of the disk detection microswitch is fine. I learned when gently moving the spindle manually just before inserting a disk (or pushing the microswitch) the spindle starts then. Also, when manually moving the spindle gently with a inserted disk it immediatly starts to spin.


Has anyone an idea what could be broken? I found a 20 year old thread about exactly the same issue somewhere else but unfortunatley with no solution..


Thanks in advance!

[Kin Hell]

Motor sticky?

Obviously, manually making it move allows it to spin so it hasn't lost all it's magic smoke just yet....

This could suggest either worn brushes on the armature of the motor or old lubricant solidifying slightly on the motor's bearings.

Continual use as is could burn it out, effectively allowing all the magic smoke to escape.

[retrofriends]

The spindle motor seems to be weak. It takes the most amount of current to start the motor. Once running, less current is required. As another has suggested, it could be a lubrication issue. You should be able to detect this by spinning the motor by hand (when not powered), and checking for binding. If the binding is imperceptible, check the capacitors once again. Does it make any noise while spinning? Can you use an oscilloscope to measure ripple on the motor connections? Trace back from the motor and check for a capacitor you may have missed, or one that you have replaced but could be NFG. If the ripple is minimal, the motor may simply be worn out.

Try at your own risk, untested suggestions as a last resport:
You could try to get some penetrating oil into the motor. Sewing machine oil or air tool oil. Check the oil's conductivity with a DMM if you have to squirt it under the flywheel and can't wipe the excess off (make sure it has very high resistance). FYI you usually can't get the flywheel off the motor. The head of the screw used is not as strong as the threadlocker used to secure it. Heat might be able to free it. Oh, I just thought of something, heat could also change the bearing/seal/lube on the motor and might make it work better for a while, or it could ruin the thing - but if it's dead anyway may be worth a try. Good luck.