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Turntable question for the old school engineers...

T

Turntable

Ok, so I decided to spin some vinyl tonight, and to my surprise, after having the power supply off over the weekend (I usually leave it on), I switch on the supply and hit start. The platter spins at what appears to be 78rpm no matter what speed selection I make. The indicators change when any of the speed select buttons are pressed, but there is no change in speed.

I tried the obvious easy remedies... switching the power supply on and off rapidly several times, going through the three speed selections on the 'table itself in rapid succession, even repeatedly pressing each in case of some logic flaw that may have been corrected by this action-- all to no avail. I wonder if there are known issues with the power supply and/or the internal logic of the table itself...

If anyone has any information on this problem and/or a possible remedy it would be greatly appreciated, as I have invested many many hours of tweaking into this setup and I am very happy with the results... I *really* don't want to start over, and I already sold the second unit I had quite awhile ago.

Please help!

-Alan
 
Two possibilities come to mind:

1. Faulty servo IC on the main board in the turntable.

2. Loss of one voltage rail out of the power supply. The power supply unit puts out 3 x DC supplies, 140v, 32.5v and 5v off memory. You will need to check that all three are present and actually getting to the appropriate part of the main turntable control PCB.

I have a service manual here for the SP-10MKII if that is any help.
 
Update:

I hopped in the shower leaving the tt spinning. When I came back into the listening room, I noticed the platter was spinning slower, but still a little too fast. A touch of the stylus confirmed this, and in fact it was quite warbly and unstable. 10 additional minutes and it was perfect. So presumably, as the power supply had time to warm up, or 'stabilise', everything was fine. This does make me think of capacitor issues within the power supply... but the sudden, almost instantaneous onset of the problem makes me wonder.

Upon arriving home, I fired it up again and the problem is recurring. I will let it spin a while and see if it stabilizes again but... any additional thoughts, anyone?

Thanks,

-Alan
 
Ok, as expected, after about 20 minutes of allowing the unit to run, it once again settled in and is now operating normally. This strikes me as the type of problem that is bound to get worse over time. eeeeek!

Thanks,

-Alan
 
Alan Fletcher said:
Ok, as expected, after about 20 minutes of allowing the unit to run, it once again settled in and is now operating normally. This strikes me as the type of problem that is bound to get worse over time. eeeeek!

Thanks,

-Alan
Click to expand...

Those turntables, great though they were, had a reputation for flaky power supplies. I would measure the voltages to see if they are where they should be, and that they are stable and clean. A 'scope comes in handy here.

If you don't have a service manual, you may want to take up Studio1's offer to refer to his.


Kind Regards,
David
 
Ok, I have just dug the manual out. I was correct with my thoughts on the supply rails.

You have 140V, 32.5V and 5V - all DC.

There is a diagram of the power interface socket on the supply here. It has what appears to be 4 pins, plus a flat one at the bottom.

Looking from left to right (or in a clockwise direction) they are numbered 1 - 4.

Pin 1 = 0V

Pin 2 = 5V

Pin 3 = 32.5V

Pin 4 = 140V

Bottom flat pin is also 0V.

As Alan has suggested, start by checking these rails for stability and noise. The power supply is all discrete components and there are plenty of caps, resistors and transistors - any one or more could be suspect.
 
Excellent, and thanks guys.

The power supply output is a cannon jack, with 4 pins. Obviously, without unjacketing the cable, this is most likely 4 + ground, or 3 + shield = ground. I do have a scope here, incidentally a very nice Tek 468 + DMM. My curiousity lies in the fact that I am listening to the table right now and it's as perfect as it ever was, provided I leave the supply on long enough for it to (apparently) stabilize. I can check the waveforms coming out (not handy to do so right at this moment) but I think something heat related has gone flukey. Any ideas on that plane?


-A
 
Alan Fletcher said:
Excellent, and thanks guys.

The power supply output is a cannon jack, with 4 pins. Obviously, without unjacketing the cable, this is most likely 4 + ground, or 3 + shield = ground. I do have a scope here, incidentally a very nice Tek 468 + DMM. My curiousity lies in the fact that I am listening to the table right now and it's as perfect as it ever was, provided I leave the supply on long enough for it to (apparently) stabilize. I can check the waveforms coming out (not handy to do so right at this moment) but I think something heat related has gone flukey. Any ideas on that plane?

Also, I did mean to take up Studio on his offer of a S/M. If you want to send me a PDF I would be eternally grateful :)

-A
Click to expand...
 
I'm not very familiar with that particular turntable, but I have worked on lots of other direct drive versions. If the power supply checks out OK, your problem might be mechanical. The turntable spindle is actually the armature of the motor and the fairly heavy turntable is the flywheel. The whole thing rides on a bearing on the bottom side of the motor. It is possible that the lubrication on that bearing has dried out causing some friction. As it is used, things warm up and works OK. A long shot, maybe, but it might be worth looking at.

I'm still betting on power supply problems.
 
Chuck said:
I'm not very familiar with that particular turntable, but I have worked on lots of other direct drive versions. If the power supply checks out OK, your problem might be mechanical. The turntable spindle is actually the armature of the motor and the fairly heavy turntable is the flywheel. The whole thing rides on a bearing on the bottom side of the motor. It is possible that the lubrication on that bearing has dried out causing some friction. As it is used, things warm up and works OK. A long shot, maybe, but it might be worth looking at.
Click to expand...

I would have thought if this was the case, the TTable would run slower at startup, not faster. ???

R
 
True, Bob.

But I appreciate Chuck's input just the same. I'm a turntable fanatic. This particular one has been my baby for the last 1.5 years. It's mounted on a custom plinth that sits on a 350lb slab of 3" thick marble 2' x 4'. It's leveled to within .1mm per meter on both planes using an engineering grade level graduated to .001" per 10".

The current arm in use is cannibalized from a Sumiko Projekt 1.2, running a Signet TK-7ea cart, currently tracking at 1.2 grams with an antiskate of 1 gram. All in all, it's a cheap setup that works extremely well. Speed stability (now when the supply cooperates) is astronomically good, and the dynamics are phenomenal. (anyone want an old Grey Labs wooden arm?)

A good pressing played on this table will make you want to throw your CD player and CD collection out the window...

This is why I didn't want to tear it down and rebuild. Analog Rocks...

It's spinning away happily playing Rush-Signals. assuming I don't turn off the suck-ply, it's fine. Really would like to get to the bottom of this though.

A "digital man" I ain't, but what a great album...

Just a fun fact post :)

-A
 
Alan Fletcher said:
A good pressing played on this table will make you want to throw your CD player and CD collection out the window...
Click to expand...

LOL!!! ;D In my case, I highly doubt it. Cue burn, scratches and groove skipping gets old with me real fast. :)

R
 
The service manual I have here has an extensive fault-finding chart, but you need to start by checking the voltages from the power supply as per what I suggested in a previous post.

The four pins on the XLR socket relate to the four I mention - counting from left to right.
 
Many years ago, I had a similar problem with speed control on an SP-15. I vaguely remember there being some sort of stripline "coil" on a PC board, which was part of the motor stator circuit. There was a nice fat cold solder joint on one end of the stripline trace, and when it quit making contact the platter would really take off.

I don't know if the SP10 has the same motor design, but you'll want to make sure all your solder blobs look nice and solid.
 
Last year I had the same problem with two SP10 MKII turntables. It turns out that the powersupply was in bad shape. After changing the caps (also the ceramic ones) on all supply lines and soldered some new transistors everything worked fine.

In my supplyunit (the one which can switch between 120 and 240V AC) I could trim the output voltage of the three different lines according to their values in the manual (download it at: http://www.vinylengine.com/library_model.php?make=Technics&selected_model=SP10 ).

Succes,

Martijn
 
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