Measuring TT Speed


In measuring my tt speed I am seeing the lines on the strobe bounce back and forth, not holding steady. This is a belt tt with a dc motor setup with a closed loop controller, and ideas on what can cause this? I am thinking the belt may be to tight, it is a new belt BTW...
jsman
Get the app "RPM" on your phone. Not only will it give you the speed but also Wow and Flutter.
If the belt is too tight, it may be causing the motor bearing to wobble by applying a bias to one side. Try backing off on the motor mounting screws if possible.
Is the belt made by the original manufacturer? Treat the belt with baby powder and try it again. Use only original belts. RPM is much more accurate than the strobe routine. 
WoW is every rotation, fludder is intermittent? Or is that backwards..
Been a while.. If the belt is in a grove and the NEW one is just a hair to wide, as the belt comes off the pully and out of the grove, BOING! it snaps out..

Make sure there is not a wide spot. Mark the wide spot, trim if needed (with sandpaper), and re-powder the belt.. BUT wipe and clean the pullies.. DON’T forget.. A sticky spot on a pully, can drive you nuts...
Slipping belt, whole different thing, touch the platter it stops... Slow startup.. la te da.

Regards
Hi, jsman,
What are you using for a light source to check the strobe disc? If the light isn't stable you'll get strobe "bounce".
Tom