Help: Sl1200mk2-A Different Component Values

by **OneyedK** » 13 Apr 2011 21:00

While I was doing a complete overhaul of one of my decks, I noticed some oddities:

PCB: SFDP122N11A

C211
Schematic value: 47nF --> same value in mk2 and mk2-A
Actual value: 220nF ??? Is this a production error or a non documented improvement ???

C301
Schematic value: 6,8nF
Actual value: 33nF --> this was the value of the mk2 version, not the mk2-A as this deck should be. ??? schematic error ???

Could an owner of an mk2-A please verify those values?
Or explain why one or the other might be best?
--> resistance values are correct as on the schematic

by **OneyedK** » 15 Apr 2011 11:15

As the gents from Pink Floyd would say: "Is there anybody out there"...

In the meantime, I figured it out.

C211: 47nF is the right value, some not-so-brilliant Panasonic engineer tried to dampen the response of the PLL filter, but managed to do that in the wrong place, not the brightest of ideas...
--> if you have a table with 220nF instead of 47nF (or an M3D for that matter) swap it out with a 47nF

Figured it out after simulating the entire PLL circuit.
--> mostly the multiple feedback low pass filter
Next up will be vastly improving W&F, however, waiting for Dr. Feickert to return from his business trip to get the right measurement equipment and a decent test disk.
--> will start a new topic if I succeed

C301: 33nF is the right value, it's simply a schematic error, with 6.8nF, the reference frequency (262080Hz) is too difficult to adjust.
Don't bother to look inside your table, I think the 33nF must be present or the deck would never have passed the quality check...

by **rocker65** » 15 Apr 2011 11:34

Hi,
Thanks for posting the information.
It is always usefull to have these little gems as you never know when they may be needed.
Regards

by **Shoji** » 15 Apr 2011 12:07

Hello. Is not error for component value. Main PCB you are having is original destination for MK5 version of model SL-1200 series.

by **OneyedK** » 15 Apr 2011 12:33

Shoji wrote:Hello. Is not error for component value. Main PCB you are having is original destination for MK5 version of model SL-1200 series.

Thank you for chiming in Shoji, can you provide some insight in why the compont value of C211 differs?
Am I overlooking something?
Why would put such a high capacitive load directly on the output of a comparing amplifier?

This table is in my posession for about 12 years now, and I didn't buy it new, it was supposed to be 4 years old when I bought it (could be older).
That's about at least 16 years old.
It's an SL-1200mkII-A, SFNN122S10.
As far as I know, PCB is still the one originally supplied.

by **scho2684** » 15 Apr 2011 12:47

Shoji wrote:Hello. Is not error for component value. Main PCB you are having is original destination for MK5 version of model SL-1200 series.

If the photo of the board below is the one it concerns, it is no MK5 version, this one it the old one, original MKII....

Marco

by **OneyedK** » 15 Apr 2011 12:50

Indeed Marco, that's the actual board.
Looks already a bit different than on the picture

by **Shoji** » 16 Apr 2011 16:40

Hello yes is agrree if original board never changed then is unlikely MK5 type as I make suggest before. Is may be possible then board follow MK3 component pattern from 1989 ? In any case is not error from worker on sake

For question about different component value is not to make much worry about this. Such component in area of filter amplifier part of IC is concern with the noise control plus the hysteresis control of circuit. In some place there is non sense about make change in torque here. Torque for such motor type is set by mechanical construction concerning number of poles and such like. If looking for any torque control from component change then look to current delivery control elsewhere.

by **OneyedK** » 16 Apr 2011 18:31

Shoji wrote:Is may be possible then board follow MK3 component pattern from 1989 ?
In any case is not error from worker on sake

Yes, I think so, the board is marked '88, but looking at the service manual of the M3D,
it are exactly those values.

Shoji wrote:For question about different component value is not to make much worry about this.
Such component in area of filter amplifier part of IC is concern with the noise control
plus the hysteresis control of circuit.

Isn't the hysteresis control the most important part to obtain best speed stability under dynamic load???

Shoji wrote:In some place there is non sense about make change in torque here.
Torque for such motor type is set by mechanical construction concerning number of poles and such like.
If looking for any torque control from component change then look to current delivery control elsewhere.

I never mentioned wanting to change torque.
I hope the Technics engineers chose te right balance between torque, rotating platter mass and bearing friction.
If the torque was really too low, the table would not exactly be under control, the whole purpose of direct drive.

Is it possible to increase the torque without damaging the motor???

by **Shoji** » 17 Apr 2011 11:26

Hello. Is looking at hysteresis in this case for threshold control on comparator internal part of IC. If look at hysteresis for motor then yes is looking at envelope for best performance. Not forget that with all this type of motor and circuit is 2 part. Main servo circuit is control for coarse motor parameter control plus the PLL part for fine motor parameter control. For torque is set by mechanical construction of motor and is not necessary for any change with this.

by **OneyedK** » 17 Apr 2011 12:24

Thank you Shoji!

I was under the assumption that the servo circuit only needed to be "clean". But looking more closely to it, it might be possible to make a small improvement there also.

But I'll be focussing on the PLL filter first, as soon as my measurement equipment arrives.
Messing with both parts at the same time would create a two headed dragon, impossible to tame