JVC A40 Turntable Stopped Spinning

[Ptlud]

I have a JVC A40 direct-drive turntable that I’ve been using recently after a long time of hibernation. I started noticing a very dim “bumping” sound during acoustic passages. The frequency of the bumping sound started to increase and then finally the platter stopped spinning. The syncing light is on.

Looking for advice on where to start investigating. Power supply, motor, lubrication...

Is it worth fixing?

Thanks.

 

[patient_ot]

https://www.vinylengine.com/library/jvc/jl-a40.shtml

I would start by reading the service manual. If you don't have experience working on stuff like this, might want to take it to someone that does.

 

[Fritz411]

It might be the auto-return gears that sit below the platter

 

[willyrover]

To elaborate on what Fritz411 said, pull off the platter. In the exploded view it looks like there is a large gear driven by a pinion on the motor shaft. The large gear has a notch (circled) that allow it to disengage from the pinion during normal operation.

If the return mechanism is out of adjustment or jammed (i.e., the pinion is not sitting in the notch) it could be stalling the motor.

Can you turn the platter by hand? or does it feel jammed?

 

[dr*audio]

Spin the platter by hand. If it spins freely and you hear no rubbing sounds, the problem is electronic, not mechanical. Try 45 rpm and see if that works. If so, clean the speed switch.

 

[Ptlud]

To elaborate on what Fritz411 said, pull off the platter. In the exploded view it looks like there is a large gear driven by a pinion on the motor shaft. The large gear has a notch (circled) that allow it to disengage from the pinion during normal operation.

If the return mechanism is out of adjustment or jammed (i.e., the pinion is not sitting in the notch) it could be stalling the motor.

Can you turn the platter by hand? or does it feel jammed?

View attachment 1080061

The platter spins freely by hand.

 

[Ptlud]

Spin the platter by hand. If it spins freely and you hear no rubbing sounds, the problem is electronic, not mechanical. Try 45 rpm and see if that works. If so, clean the speed switch.

The platter spins at 45, but I cannot sync the speed using the pot.

 

[dr*audio]

First thing to do is clean the speed switch and the pot. Open the bottom and inject the cleaner into any opening in the body of the pot and the switch and work them back and forth 30 times. De-Oxit works best.

 

[Ptlud]

First thing to do is clean the speed switch and the pot. Open the bottom and inject the cleaner into any opening in the body of the pot and the switch and work them back and forth 30 times. De-Oxit works best.

Progress:
(1) Cleaned the speed switch with De-Oxit D5 and now the platter spins at 33. Am able to get the speed consistent, but then the speed varies.
(2) The platter spins at 45, but there is not enough adjustment to get the speed to synced.
(3) The bumping sound continues to be heard through the speakers at about 2 Hz using my new Mani phono preamp as well as my older preamp.

 

[dr*audio]

Put your ear up to the turntable and see if you can hear the sound as it spins.

 

[Ptlud]

Put your ear up to the turntable and see if you can hear the sound as it spins.

(1) I cued the tonearm and set the speed to 33. I could not hear any sounds at all. Quiet.
(2) With the power off, I rotated the platter with my finger at different distances from the center and felt no anomalies.

I don’t think there is a physical cause for the “bumping” sound. Could it be a faulty capacitor or transistor in the power supply for servo driver boards?

 

[dr*audio]

Do you have a strobe disc you can use to see if the speed is varying?

 

[Ptlud]

Do you have a strobe disc you can use to see if the speed is varying?

The stobe light is working and I am able to stabilize the speed at 33 only for a moment, and then the speed starts varying. I am not able to get the 45 speed stabilized at all.

 

[dr*audio]

try adjusting VR3 for the midpoint of the window where the speed is stable.