lsorrentino
New Member
Hello all, I'm trying to fix a Sansui turtable, last thing I had to fix was the platter rotation that was not completely stable, I had 0.22 speed variation, to make a long story short the problem was in the tachometric PCB alignment, after some work and some unsuccessful component substitution I found that a non constant amplitude feedback signal cause the speed variation, due to a non symmetric characteristic of the squarer before the PLL ic.
My method was to make the motor run without platter and find the better positioning and after tight the six screws.
In yellow the tacho signal before alignment:
After alignment I obtained an acceptable 0.05 wow, not as good as declared but fine respect to the starting point.
The motor drive circuit diagram, I found that the squarer eIC2a in the schematic, is not symmetric in its I/O function, even if I replace the component, this is probably due to the time it keeps exiting from saturation, positive and negative are not equals, below the plot:
Anyone experienced with this kind of repairing can help me? Any tip?
Thanks in advance and best regards,
Luca
My method was to make the motor run without platter and find the better positioning and after tight the six screws.
In yellow the tacho signal before alignment:
After alignment I obtained an acceptable 0.05 wow, not as good as declared but fine respect to the starting point.
The motor drive circuit diagram, I found that the squarer eIC2a in the schematic, is not symmetric in its I/O function, even if I replace the component, this is probably due to the time it keeps exiting from saturation, positive and negative are not equals, below the plot:
Anyone experienced with this kind of repairing can help me? Any tip?
Thanks in advance and best regards,
Luca