PT One motor identification

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TSwede
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PT One motor identification

Post by TSwede » 28 Sep 2016 23:32

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Motor
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Hi all... long time since I posted but the PT has been ticking along nicely for ages! Now however it is not as stable and has a bad flutter on 45rpm. I bought a Funk Vector drive mounted in an Anni psu box on eBay and hope to connest it up as a repair/upgrade but the Funk has two wires coming out of it and the motor has 4 going in so there will need to be some fiddling... can anyone help me ID the motor and the specs and which wire does what? If it isn't going to be suitable I could consider either a repair to the original Board or a replacement motor to go with the Funk Vector Drive... here is a pic of the motor... thanks all
Last edited by TSwede on 28 Sep 2016 23:38, edited 1 time in total.

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Re: PT One motor identification

Post by TSwede » 28 Sep 2016 23:33

Oh dear no picture! Hang on I'll try again

tim_bissell
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Re: PT One motor identification

Post by tim_bissell » 30 Sep 2016 00:24

Hi,

The motor is the Escap (now Portescap) DC tacho motor; two wires (usually blue/purple) are for the motor DC input, and the other are the output of a DC tachometer / generator. The Speed controller uses the tacho output to regulate the input voltage.

You should be able to check which is which by taking a photo of the wires as they currently go into the board (just for safety!) and checking the lettering on the underside of the PCB; there should be + M T + or something similar by the connector block.

You may be able to drive the motor from the funk firm controller, but I don't know if the voltage would be correct or safe, so I would not try it without checking with Funk. Realistically it would be better to fix the original controller.

Having a speed variation on just one speed does not sound like a motor problem to me, more like the controller. Fortunately the controllers are simple, and the parts are readily available the problem is most likely to be the electrolytic capacitors, which are getting old and drying out, or possibly a dirty or bad connection in the rotary switch. There are only three electrolytic capacitors so I would be inclined to replace them anyway, and maybe squirt some contact cleaner into the rotary switch.

Where are you based? There may be people nearby who can help if necessary.

-- Tim

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Re: PT One motor identification

Post by TSwede » 30 Sep 2016 10:15

Hi Tim
That's brilliant thanks
An electonics engineer friend assisted me last night and we managed to get the funk tidied up a bit and got the output voltages to match those of the PT circuit. We thought we'd cracked it at that and I was just going to make a fly lead to connect the PT to the funk box. We have only connected up two wires for the voltage.. so if I am going to go with the funk.. which I'd rather do now, then we're gonna have to figure out the servo input. Can't be too many choices because there was a five pin din on the funk board and we've used two and one is earth... i could do with a pin diagram for this really. The PT circuit does not look easily removable without taking the top off.. also I've now removed the 33/45 switch so I can grommet the hole.. so it would be better for us to try to figure out how to connect the servo on the theoretically more modern and better funk (think it's from 2005).. so any tips or pointers would be most welcome... missing playing me records!!

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Re: PT One motor identification

Post by TSwede » 30 Sep 2016 10:38

Here's a couple of pictures the Vector drive.. just need to find out a bit more about it if poss and find them servo inputs...
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Alex M
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Re: PT One motor identification

Post by Alex M » 30 Sep 2016 11:31

I have a feeling that the Funk Vector system used more than one motor over the years - presumably a given drive will only be properly suited to the motor it was designed for? Just for information, my Vector upgrade, which Arthur installed about ten years ago, used a Premotec motor. The Farnell listing for this motor is

Orde code: 147875 ALLIED MOTION PREMOTEC 9904-120-18105 DC Motor, Coreless, 2.9 W, 3840 rpm

Note that the Vector motor is NOT a servo motor, and only has two connections. As I understand it, the K-Drive controller uses a current sensor, instead of servo feedback (which was used in the Anniversary).

Alex

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Re: PT One motor identification

Post by TSwede » 30 Sep 2016 11:39

Ahhh right... so if this is the case then this drive will never work with my motor unless the circuit has a servo feedback function.. ? Which you don't think it has.. i''m hoping someone can look st this thing and tell by looking at it if it is current sensor or servo feedback... if it is in fact current sensor and I need to change motor I need to try to do this without taking the top plate off the deck.. I'm trying to minimise physical disruption.. I presume a current feedback circuit won't work properly with a motor like mine? Even when connected concentionally without the servo wires?

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Re: PT One motor identification

Post by Alex M » 30 Sep 2016 14:16

Farnell still stock the Premotec motor (£56 plus VAT), so you could give this a try with your controller, but you would of course need to put a pulley of the correct diameter on it to get the right RPM.

I would suggest you contact Funk for advice.

Alex

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Re: PT One motor identification

Post by TSwede » 30 Sep 2016 14:25

On an aside I wonder where the earliest known PT is?? Might put a post on if it's not already been done

tim_bissell
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Re: PT One motor identification

Post by tim_bissell » 01 Oct 2016 11:02

I'm not knowledgeable about electrical circuitry beyond A-level physics thirty years ago, so I am not sure if brushless motors work with the current sensors or not; I think they should do. If that is the case, and the Funk electronics can be trimmed down to the 33 you can quite happily ignore the servo wires (tape the bare ends, please don't cut them off!) and use as-is.

If you do decide to go with a new motor and pulley, I am sure a few people (e.g. me!) would be happy to buy the old motor off you!

However, the top plate is exceedingly easy to remove and replace on the PT1:

Find some imperial measurement allen keys, and loosen the grub screw in the back of the triangular acrylic speed switch, then remove it. There remains one (or is it two? not at home so I can't check) small cross-headed screw(s) which fasten the top plate onto the suspension mounts; unscrew these and it is held in place by some small strips of double-sided sellotape foam - I pull the plate up from the armboard side, and use a solvent to clean off the sellotape residue.

You can still find these foam sticky pads in DIY stores, and replacement of the top plate is straightforward - it is nice to find a turntable which is so straightforward to assemble and disassemble.

Note: If you are leaving the bearing spindle in place, wrap and tape it in some protective foam sheet or bubble wrap to avoid damage to its surface or the jewel.

The old speed controller was usually held in place with a couple of screws through holes in the PCB. Again, you could probably find someone willing to buy and refurbish it.

As to the oldest PT turntable around; I am fairly sure there was a thread on this sub-forum about it; someone spotted a very old-looking designation on eBay a few years back; the topics here can be quite illuminating and are not to numerous to skim through if you have a few hours. One of our members (Pinktrichard?) worked at PT for a while, after buying an early one.

From what I have read, the very earliest had a glass (three-piece) top plate, a sliding switch for speed control and a different servo motor - I think its servo output AC and the controller design was different. However PT did provide upgrades for their turntables so I would imagine a lot of early ones were upgraded, as a lot of PT1s were updated to the PT TOO spec.

-- Tim

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Re: PT One motor identification

Post by PinkTrichard » 01 Oct 2016 22:32

The very earliest turntables had a slider switch which was gorgeous but fell apart. I'm not sure if any remained with punters or whether all were modified with the thorens style switch which preceded the acrylic triangle. My original was no 47, but I replaced it at the factory. My current model although a fairly early serial number is like triggers broom, with the serial number being about the only original part.

Early PT 1 like mine used a matsushita motor which was servo controlled. I am no expert in electronics either but I happen to have Owen Jones staying with me this weekend. He designed a new board for the pt1 and used a Swiss motor with a tacho - which is the one you have here.

In theory the vx electronics could drive that motor and just ignore the tacho. A motor without a tacho is controlled by a servo loop measuring the back emf of the motor. But the circuit needs to to be configured for the motor.

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Re: PT One motor identification

Post by TSwede » 03 Oct 2016 14:22

This is really helpful!! And interesting!! I particularly like the historical stuff and the fact that the chap who designed the drive on my much loved old turntable is still knocking about somewhere in turntable world!! Thanks Owen! It's a great design.. worked fab until just a few months ago! I've sent a couple of pictures of the Vector drive circuit to Arthur at Funk in the hope that he can tell me if that circuit would hold my original PT motor stable just using two wires.. or is it a tacho circuit that could use four wires? Or does it simply need another motor.. i'd like to know in advance of reassembly what is the best option because I only want to put it back together once.. so here's hoping!!

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Re: PT One motor identification

Post by PinkTrichard » 05 Oct 2016 16:14

As Tim noted - a PT1 is not hard to take apart and put back together again (a PT TOO is a different prospect altogether). The control mechanism is going to need to be adjusted to the particular motor. The Vector circuit does not make use of a motor tacho - it controls the motor voltage using a feedback circuit which measures the motor EMF and uses this feedback to control speed. It does not get a tacho signal to measure speed. So just 2 wires. But I would not be surprised if Arthurs response is not to tell you to use the motor the circuit was designed for.

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Re: PT One motor identification

Post by TSwede » 05 Oct 2016 20:06

Hi.. I'm half tempted to take the top off just to get the old circuit out so it can be put to good use by someone and if I have to change the motor I will... Arthur reckons this version of the K Drive could drive the escap motor with some specific instructions from him about the trim settings etc so I'm going to give it a go... if it doesn't work I'll have to change to motor and l'll be selling the escap motor and the original drive.. i'll tell you how I get on!!

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Re: PT One motor identification

Post by TSwede » 20 Oct 2016 17:07

You know - after much fiddling around and reassembly this is nearly (in italics!) working! I've still got a bit of fiddling around to do but the best I can get to is that it stablilises to a good speed after running for a few minutes too slow.. I have redone all the geometry, made a new ballast weight for the Rega armboard.. fitted the Michell VTA adjuster and all that and the deck sounds bloody amazing! However only after a few minutes.. so - I'm going to have to bite the bullet and get the Premotec motor.

So the top plate will have to come off - which I have had some advice about (thanks Tim). I do have a question though.. how do I get the pulley off my old motor and onto the Premotec one??

Thanks all

Tony

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