PT1 servo disaster

[Eric van Spelde]

Longstory short: I've got only one speed anymore - too fast. Removing/putting back either of the two wores to the servo in the Escap motor doesn't make any difference.

Background: was making a new bottom cover and one of the servo wires came undone while test fitting, so the top plate had to come off. Then I tried my new battery PSU (and yes, I did make sure the connection into the TT is tip positive) - nothing, hooked up 9V wallwart supply - problem.

I hope I only burnt out the servo board and not the motor servo in the Escap...

Not the first time the speed control has let me down, either. Might be time to have something rather more serious/robust made - if the motor has survived that is.

Not the weekend hifi tweaking I had anticipated on...

[Steerpike_jhb]

Difficult to say without seeing or knowing the motor model, but the servo sensor is probably just an induction coil. Very thing wire, so it could break if the solder tag was stressed. An ohm-meter should show a low-ish resistance on the tacho pins of the motor - tens to hundreds of ohms.

[tim_bissell]

Difficult to say without seeing or knowing the motor model, but the servo sensor is probably just an induction coil. Very thing wire, so it could break if the solder tag was stressed. An ohm-meter should show a low-ish resistance on the tacho pins of the motor - tens to hundreds of ohms.

If it is the Escap motor, it is the Escap HL 11 213 E 204 1 model (23mm diameter)

I I get a chance I'll check the resistance of one of mine... if the motor is running, you should get a DC voltage across the servo wire (someone correct me if I am wrong)

-- Tim

[Eric van Spelde]

Update: it's at my repairer/modifier of choice and the way I understand it so far, they got inconclusive results on measuring the whole caboodle but it's very probable the servo on the Escap is borked.

The route forward will probably be some sort of optical sensor drive system, either using the existing motor disregarding its servo, or one of a batch of Maxons they happen to have lying around, although these are ball bearing variants and as of yet they're not sure of the suitability of those for use in a TT.

On the upside the arm will be wearing an SPU Royal N when the PT returns. I'm sure these particular folks (designers of Pink Faun gear) will come up with something rather more advanced, not to mention stable, than the 1983 Arthur K. servo board, too.

I'll keep y'all posted.

[Eric van Spelde]

Right - 't wasn't so bad after all. Op amp and some other stuff replaced/upgraded on the servo board, motor is fine. 9V DC Battery PSU placed in nice metal housing with brushed alloy fascia and switch for either running the deck or charging the battery; SPU Royal N installed. Output goes into Audio Innovations series 800 step up. Pretty much the ultimate non-Vector PT now.

First impressions over the weekend are very good; more detail, but also individual sounds have more body and energy than before. The analogue rig now edges my rather excellent cd set up (modified CEC TL5100 transport/modified Audio Note DAC One.1x Signature) once more...

[tim_bissell]

That is great news!

Glad it sounds good; where did you get the battery PSU?

cheers,

Tim

[Eric van Spelde]

Matthijs of Triple M/Pink Faun made a small circuit for me that outputs a clean 9.00 V DC from a 7A, 12V lead acid battery that I bought for this purpose earlier. A wallwart 12V charger tops up the battery when not in use, with a dipswitch to choose either charging or DT output.

Then they put it in a nice metal box for me that they normally use for some of the Pink Faun equipment... Works like a charm, although the double sided tape wasn't enough to keep the battery in place within the case during transport.

[tim_bissell]

Hmmm... sounds like a project - I could get all those bits from Maplin (although it would be just a basic kit-based voltage regulator circuit. I have peered at all the batteries available, wondering how many Ampere-hours I would need for it to be practical!

-- Tim

[natty_dredd]

And me....

I keep picking up 12V sealed gel batteries as they get dumped by workmen where I live. Perhaps no good for higher current purposes anymore but certainly ok for lower current things and I ran a class-T amp off one without even charging it for days with no loss to terminal voltage.

There is supposed to be a lot of noise from lead acid batteries (I guess chemical reactions happening randomly) so might need a fair bit of smoothing via caps but perhaps not a concern for turntable psus.

I don't think you'd need that many Ah, current is going to be fairly low I'd have thought.

As I say, people chuck away (recycle) 38Ah batteries at work sites that are absolutely fine for this sort of thing - i got my first from a theatre I worked at which were now rubbish for their genie/cherry picker thing but perfect still for hifi.

Must make sure they are properly fused though as you can weld with the current these things put out when shorted... including inrushes into too large capacitors!

[Eric van Spelde]

Took a piccie the other day... It's simple but more than adequate giving an output variation of <0.01V under load....

[Zebulon_minor]

Eric,

That is a thing of beauty, I *really* would like one for my Anni, come to think of it, for my PT1 and FFV too.. You wouldn't have any closeups of the circuit board, perchance...?...

Z_m

[Eric van Spelde]

I might have the original drawing of the circuit by Matthijs, somewhere at home... I'll look and ask his permission for putting it up here, provided I do find it.

[Zebulon_minor]

Eric,

That would be the bees knees, I recon a lot of us here on this sub-fora would be very excited if it were possible

Z_m