good evening,
a dear friend of mine gifted me his grandfather's turntable (i cannot recognize the model). i changed the belt, i put some oil in order to lubricate it properly but i still have some problems: the turntable speed is too slow (not so much) and the pitch regulation has reached the limit.
i decided to remove the bottom and give a look inside in search of some trimmer, i found two of them (33 and 45) but they are not working. inspecting the pcb i noticed a scratch on the board that cut off the two variable resistors.
i really don't know how a FG servo works i found no datasheet for the IC neither for the motor so i decided to ask here for an help
a dear friend of mine gifted me his grandfather's turntable (i cannot recognize the model). i changed the belt, i put some oil in order to lubricate it properly but i still have some problems: the turntable speed is too slow (not so much) and the pitch regulation has reached the limit.
i decided to remove the bottom and give a look inside in search of some trimmer, i found two of them (33 and 45) but they are not working. inspecting the pcb i noticed a scratch on the board that cut off the two variable resistors.
i really don't know how a FG servo works i found no datasheet for the IC neither for the motor so i decided to ask here for an help
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Offhand I don't think you need to know all these things - just seeing those traces cut in the last photo suggests to me that it would work if you jumpered them over and adjusted each trimmer so is runs at proper speed with the front-panel speed control in the middle of its travel.
today i will try to fix the traces, then if it doesn't work i will replace some capacitor.
my question is: why are the traces broken?
it's quite strange now they are visible.
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It appears that these traces were cut with the intention of bypassing the speed control adjustments. Hard to know why it was done (what problem was being solved), but a good start is just laying a cut off resistor leg along the trace and soldering it down on both ends. This should restore the function of the trim pots.
See what the behavior is like when the pots are back in the circuit. Troubleshoot from there, if necessary. If things are still not working, I second the vote to go after caps. After ~15 years, caps are a random element. The goods is they are cheap and plentiful!
See what the behavior is like when the pots are back in the circuit. Troubleshoot from there, if necessary. If things are still not working, I second the vote to go after caps. After ~15 years, caps are a random element. The goods is they are cheap and plentiful!
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sorry, i had to study a lot the previous week for some engineering exams, now i'm back to life 
i fixed the traces, but nothing is changed i mean it continues to be a little bit slow and moving the trimmers nothing change. i checked the trimmers with a ohmmeter and they are ok.
it's the first thing i've done, it spin very freely.
anyway i fixed temporarily the problem applying some scotch (0,3mm) on the motor pulley and i reached the correct speed anyway now i have 2 ways:
-reduce the diameter of the bigger pulley
-fix the board
there is another way i think, what about build a regulator with arduino? it should be easy i think, the only problem is that i really don't know how the motor feedback works.
i fixed the traces, but nothing is changed i mean it continues to be a little bit slow and moving the trimmers nothing change. i checked the trimmers with a ohmmeter and they are ok.
it's the first thing i've done, it spin very freely.
anyway i fixed temporarily the problem applying some scotch (0,3mm) on the motor pulley and i reached the correct speed anyway now i have 2 ways:
-reduce the diameter of the bigger pulley
-fix the board
there is another way i think, what about build a regulator with arduino? it should be easy i think, the only problem is that i really don't know how the motor feedback works.
I believe the reason the adjustment pots are not doing anything still is because the yellow and white wires under the pcb have been moved , probably from the 33 and 45 holes on the lower right of photo 1 . I have found a similar pcb layout on the Garrard GT 55 , you can download the service manual for this on vinylengine.com . It uses the same IC as yours and there is a reasonable schematic which would at least give you more info .
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