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Philips GA312 Turntable

eckmyredavid461920's picture

I have this unit (listed above) in for repair, and I'm more about the big amps and guitar amps....however, the boss put this in front of me and told me that the table turns at an inconsistent speed. I have the spec for adjustments, but that's at a stable running speed, which is not the case here.

I need the turntable gurues to give me an insight of why this table is turning at inconsistant speeds. I believe that the motor has developed a flat spot on the windings, causing an inconsitency...am I close??

Inconsistent speed GA312 TT


First of all: Check the power supply smoothing capacitor, most grey ones are leaking by now.
Causes all kinds of problems, including yours.

Did you check the preset- AND the adjustment pots on the PCB? TWO for each speed.
They tend to get very dirty or corroded (or even crack when stored very cold).
Measure the output voltage to the motor and just push the pots sideways with a screwdriver.
Any change in measurement?

Have a look at the signal coming from the tacho generator inside the motor using a scope.
You should do this with a constant DC source driving the motor, bypassing the electronics.
Motor should be completely detached from the PCB.
Tacho generator can be defective, but I have seen this only once.

Motors from GA212 and GA312 are identical, should not be hard to find a scrap one.