Technics Sp10 MK2 instable phase tracking

[Needles]

Technics Sp10 MK2 unstable phase tracking

Hi all,

Last month my SP10Mk2 was behaving very strange at all speeds.
It made a lot of noise and the revolutions were erratic; speed was
increasing/decreasing but never stable.

After dismantling the SP10 from the console noise was gone but the speed was still unstable so I decided to replace C2,C4 and C6 on the Drive Circuit
Board and the Control Circuit Board got two new blue multi turn pots
for VR101 en VR102 . Checked the oscillator (was 54 KHz.) and set it
to 50 KHz. (960mVpp)

Now I was able to adjust the phase tracking :
33 1/3 > -6,2 ms.
78 > -2,6 ms.
45 rpm was within limits.

However these figures are not stable.
Now and then they jump to different values....and back.
33 1/3 jumps to approx (+)12 ms
45 to (+)10 or 24
78 to (+)5,8.

RPM check (RPM app on iPhone) w/f measures 0,14% and speed is a little
high at 33.39.

The SP10 is back in the console for three weeks now and the
disturbing noise was not heard so far....
Any ideas for improvement and/or double checking other values ?

Greetz !

 

[warrjon]

I would re-solder ALL joints on every PCB, it's a big job but worth doing. I found at least 6 dry joint over the 3 PCB's and these were only the ones I could see.

When you say you adjusted the 50kHz what did you adjust.

When I repaired my SP10 I found the adjustments needed an iterative approach as someone had put them way out.

 

[Needles]

Technics Sp10 MK2 unstable phase tracking

I would re-solder ALL joints on every PCB, it's a big job but worth doing. I found at least 6 dry joint over the 3 PCB's and these were only the ones I could see.

When you say you adjusted the 50kHz what did you adjust.

When I repaired my SP10 I found the adjustments needed an iterative approach as someone had put them way out.

When I changed T1 (on SFDB102-08) not only Vpp but also the frequency is adjustable.

After some more finetuning with VR101/VR102 figures are stable now.
But..
When selecting 78 rpm now and then the strobe switches off.
I checked for Voltages and starting at 33 rpm there is a approx. 6 Volt drop for every step upwards (45/78). (and increase going down)
In cases where the strobe switches off I measure 0 Volt....
I get the same symptoms with the speedselector disconnected while manual shortcutting 33/45/78 to O Volt. 140V under load looks OK.
I am lost...

 

[JonSnell Electronic]

Check the feedback pulses are stable and approximately 10v p-p.

 

[warrjon]

When I changed T1 (on SFDB102-08) not only
When selecting 78 rpm now and then the strobe switches off.
I checked for Voltages and starting at 33 rpm there is a approx. 6 Volt drop for every step upwards (45/78). (and increase going down)
In cases where the strobe switches off I measure 0 Volt....
I get the same symptoms with the speedselector disconnected while manual shortcutting 33/45/78 to O Volt. 140V under load looks OK.
I am lost...

Intermittent faults a classic symptom of bad solder joints/connections.

I would pull the PCB's and re-solder ALL components, also check motor connector for corrosion/crud in the plug/pins. I was a bench tech for Marantz and any intermittent fault the first place to start was checking for dry joints, although my eyes were better in those days. I would almost guarantee this will fix your intermittent issues.


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