Hello there,

I tried searching the internet and the forums here, but so far have come up with only some basic circuits that do not quite serve my needs, so I am turning to some of you guys as the guru's that may be able to help me out for repairing a circuit for a piece of audio gear that I am restoring. Let me explain exactly what I need...

I have a very rare and unique vinyl record player turntable called a "Transcriber" made by "Transcriptors" of ireland. My turntable is rather unique in that the headshell/cartridge/needle assembly is mounted directly to the glass lid and does not move with the grooves of the record via a tonearm like a standard record player normally does. Instead, the platter and record move under the needle driven by a motor that turns a set of gears riding along a set of guiderails with the platter spinning on top of it that moves horizontally under the needle thus playing music via a sensor on the needle assembly that detects if the record needs advancing.

Basically what happens is there is a little lever that is mounted to the headshell that breaks a lightbeam when it is in alignment and does not need to have the record advance, but as it gets out of alignment and needs to turn the record advancing motor, the lightbeam then becomes visible by the detector in the circuit and runs the motor as necessary until the beam is once again broken by the lever as it is advanced thus stopping the motor until once again the light is visible by the detector and requiring the motor to advance again.

The problem of this circuit is that the unit is very old and the sensor is no longer functional and will no longer advance the record platter to realign the headshell properly. It is more than likely due to the fact that the little light that was used in the sensor has long burnt out (this unit was made in the late 70's - early 80's) and is super rare and quite valuable - and very unique. I would like to completely replace the control circuit for this unit and update it to a very accurate LED controlled circuit that will very accurately track the position of the headshell and drive the platter alignment/advancement motor at a very low and steady speed to move the platter along its rails properly so that the record can be listened to properly.

I hope that somebody here could help point me in the right direction on this project and shed some light in my direction. I would be grateful to any and all suggestions in that regard. Please feel free to ask any and all questions. I think that I have explained what I need clearly, but here is a few links that may help show what I am talking about.

The motor that I need running uses 12v when I advance it manually at full speed to position it via a switch either backwards or forwards to set the start position, or "rewind" the record position back to the start, and can run from anywhere 3v-8vDC while tracking.

http://www.youtube.com/watch?v=vbAROj46e-0
http://www.youtube.com/watch?v=IQ_r0Vk9Ct8 <---- this one really shows how it works...

Thanks for your time and any help or guidance that you may provide...

Cheers,
Chris

The simplest way would be to replace the bulb. What is the number marked on the bulb? If you can't get the bulb then you will have to measure the voltage, and if it is AC or DC. Then we could probably cross-reference it.

Yes that turntable is probably quite valuable so don't modify it unless absolutely necessary.

I agree with Bob,
That it would be easier to just replace the bulb,
keeping it as original, as you can.

But, if finding a bulb is a problem.
You could probably be able to use a LED as the light source instead.
I know guys who rebuild older stereo receivers {60's to 80's vintage}.
And use simple resistor & White LED's, to replace the 6V or 8V display bulbs.

I'd consider doing that, if it's not to much trouble modifying the bulb assembly.


Signed: Janitor Tzap

well, to be honest with you, I tried just replacing the bulb, and also just shining the light on the components to see if that was just the problem, but there is also something else that is not working right, and to get a bulb for this thing would be really tough, it is so tiny and no, there is no number on it. I would love to rebuild the turntable control unit with a newer style so that it would work even better than the original with updated style components. The circuit is not all that complex to begin with, however some of the components I cannot tell what values they are by looking at them. There are some diodes that I cannot tell what the values are, and would love to design something different for this unit. I will also have the original circuit if I ever decide to sell it, but I am planning on keeping this one around for a while, so something new would be preferable.

The old circuit was a bit sporadic and I would like to make something that would work a bit more consistent and smoothly. I don't think that the circuit would be too difficult to design, I just really do not have the knowledge to come up with something that would work exactly for what I need.

I have done an extensive search for some circuits that KINDA do what I want, and I was thinking of modifying one to work with this application.

We'll see how it goes.

BTW, I also live in the Vancouver area, (Aldergrove actually). Nice to see another BC'er here.

Cheers
Chris

Hey Janitor,

That was my first try was to replace the bulb with an LED, and it DID work - as in the light did light up, but unfortunately the circuit did not work. It would not drive the motor. It really is quite a simple circuit, as it only had a bridge rectifier, a couple resistors, a transistor, and a few diodes. I tried replacing the Bridge rectifier, and the transistor, measured the resistors and found no problem with them, but the couple of diodes I could not find any markings or numbers on them that would help me source a replacement, so they remained untouched. I am not sure whether or not the photosensor was working properly, but the value seemed to change in resistance due to the amount of light that hit it, so I think that was ok. Still the motor would not budge. So There it sat and I have not touched it since.

I would still like to have a more up to date circuit using an LED and LED phototransistor sensor that drives a PWM motor controller instead of just straight DC voltage applied to the motor.

The circuit does not have to be that extravagant, just something that varies the output increasing with light intensity. Maybe I will dig up a couple of designs that I located, and maybe someone could possibly suggest some tweaks to the circuit that would provide the results I am after. Would this be the proper way to go? I will look through my notes and see what I can come up with.

Thanks again,
Cheers
Chris

Chris,

I did some digging and came up with this website.
http://www.transcriptors.net/turntables.htm

They seem to be still around in the UK.
Also they list the {Transcriber} Turntable that you have.
Plus, offer replacement parts and service for it.

Hope this helps.


Signed: Janitor Tzap