Technics 1210 internal regulation mods

[Mike_New]

Hi Martin and also Paul,

Looking at the image of Martin’s PCB indicating where the track should be cut, alerts me to a possible improvement. Looking at where Martin has marked a line to separate the 21V supply into two separate supplies.
You will notice that there is another track on the RHS of the cut, which goes up to the motor coil assembly. This track supplies the common 21V to the three pairs of position-detect coils, which are stimulated by the ‘star wheel’ on the underside of the platter.

I believe that for the ultimate isolation from the drive motor, these coils should also be fed from the second 21V supply.
This can be achieved by cutting the track at an angle where the DR is in the word ‘DRIVE’ as shown in Martin’s image of the PCB.
This then leaves these coils to be supplied by the second 21V supply.

[MartinT]

I've been looking at it and the circuit diagram, Mike. Interesting, however it seems to me that those sense coils are leading into the motor drive chip IC101. I'm not sure how that IC would behave with two different power supplies to different parts of it (albeit through one of the coils - P1)?

[Mike_New]

Hi Martin,
This could be possible, but if you look at the 'Block Diagram' of the system the coil inputs really are just another set of circuits within an IC with a common supply voltage which powers the various internal active components as well as being the current source for the motor coils.
I suppose my idea could be accademic, since the active components of the position dectect coils and the oscillator and comparators are powered by the 21v motor source.

[MartinT]

I was thinking that common mode noise could be worse if the power rail for the coils was different from the power rail for the IC electronics. Paul will no doubt answer this when he takes a look.

[Wakefield Turntables]

Lovin these posts! I honestly cant wait for 2012 to get started, mainly so things can get back to normal and then the 1210 can have its next phase of updates!

[Artifolk]

I'm sitting comfortably waiting for the results... even though most of this electronics malarkey is going straight over the top

[Paul Hynes]

Mike and Martin,

At this point I could not say what the effect of separating the coil supply from the AN6675 supply would be, as I have not tried it. With systems like this, where details of the chip circuitry are not generally available, it is a difficult prediction to make from just a block diagram (which incidentally has errors on it). Some experimentation will be required to verify the results. I will look into it further once I have my current projects out of the way. It is not going to make any difference to the current internal regulator upgrades, as it would be an easy retrofit to add another regulator.

Regards
Paul

[Pete]

Bravo Martin!

I've fallen behind

Now I need to order the TDR-21 custom dual regulator module from Paul.

I assume Paul provides info on what resistor must change on the SR5-21 to convert it to 27V output?

Cheers
Pete

[MartinT]

It's straightforward, Pete. Just open up the SR5 front panel (the end with the LED) and you will see an adjustable pot with a small screw on the PCB. Using a digital voltmeter, turn it until you get 27V.

With your system resolution, I think you'll find the mod very worthwhile.

[Pete]

It's straightforward, Pete. Just open up the SR5 front panel (the end with the LED) and you will see an adjustable pot with a small screw on the PCB. Using a digital voltmeter, turn it until you get 27V.

With your system resolution, I think you'll find the mod very worthwhile.

Indeed! But according to Paul I have to check my regulator because it may have older parts not rated high enough for the 27v output. Time to crack open the case on my DIY SR5.

Isn't this fun?