Sony WM-DD33 speed issues (and more..)

Is it normal, even when in sync, to see impulses on Pin 9? Or should it be more like a constant value?

 

A little bit more information. This picture is the voltage at the motor when it is locked. Are these spikes normal operation? Could this be a symptom of some mechanical issue that makes the voltage rise because the feedback loop detects it is slowing? Could this then trigger the speed issues?

 

Today I've received and restored to kind of working state DD22 from ebay, so new discoveries are in the way.
In the next few days I'll check the waveforms, auto stop theory and everything else

But for now, I want to say I love how stable quartz lock playback is, especially on electronic music. Day and night compared to FX877, even with partially disintegrated rubber ring on disc.

 

OK, so I could't sleep without some experiments.
So here are a lot of waveforms for every pin of servo IC601 CXA1423, recorded from normally working Walkman DD22:

PIN1: Signal from FG coil, around 200mV P-P, 1.2V offset from GND
PIN2: 90mV P-P, 1.2V offset from GND
PIN3: FG amplifier output, limited to 1.6V
PIN4: Sawtooth, 0 to 1,26V. Stable, without peak fluctuations.
PIN5: VRef, very stable 1.62V
PIN6: Very small downpeak, somewhat similar frequency to pin 9
PIN7: Power on input, 2.7V
PIN8: Power, 2.8V
PIN9: Short impulses, 2.6V P-P, about 1kHz frequency, duty cycle depends on motor load.
PIN10: Short impulses, 600mV Peak, about 1kHz frequency, peak voltage depends on motor load.
PIN11, PIN12: some stair type signal, height depends on motor load
PIN13, PIN14: Motor current request amplifier, depends on motor load
PIN15: Motor transistor control output, depends on motor load, 2.1V offset from GND.

Also, pin5 of IC701 signal is similar to Pin4, not so stable, but also not going to 6V as on my DD33.

 

Also, signal on PIN9 highly correlates to signal on pin 4.

Hope I will not be banned because of too many images in 1 post

 

Also, measured voltage directly on the Motor+ output.
Correlates with Pin15 with the IC, no tiny peaks of voltage as on your graph. Maybe motor is getting old? Frequency is very high, does not look like interference from control circuits, and spike goes up, meaning lower impedance on motor at those moments (or also could be interference on the input of the transistor) . Try cleaning the shaft of the motor, or if it could be disassembled, also there will be a good thing to clean brushes and their contact surfaces.

BTW, are you using batteries or bench power supply to power the walkman during tests? Because 30us pulse period means about 33hKz frequency, which is similar to what some power supplies are using.