I have two Numark TT500 turntables. They each have a slider which controls the pitch (speed the motor rotates the platter that the vinyl record sits on). The problem is that 0% pitch distortion is supposed to be in the dead center of the slider, but 0% is at the very bottom of the slider, not in the center. The zero is way off center, rendering the tables unusable for DJing. (I can tell where the zero is based on the sound, and an LED lights up telling me when I am at 0)

I took the slider out of the turntable and measured two points on the bottom of a pcb attached to the slider assembly which I think lead to the potentiometer the slider uses. The resistance measurements are as follows:
~1kOhm slider all the way up
~5kOhm slider centered
~10kOhm slider all the way down

These seem about right, considering its a linear pot.

What I'm asking for is help diagnosing and hopefully fixing this problem with my off-center zeros. The bad pitch sliders are stopping me practicing mixing and enjoying my music. I would order replacement slider assemblies but Numark has been on backorder for them since around January of this year, so it seems I'm out of luck there.

Help would be very appreciated, please and thank you

 

Maybe a shorted resistor before or after the POT?

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It's incredibly rare for a resistor to go S/C, and it only happens when it's a large wattage one that's been cooked. A small resistor like this one (if indeed there is a resistor) isn't going to go S/C. If we're talking resistors, then the resistor at the other end (again if there is one) is more likrly to have gone high in value. However, I would also consider that unlikely, as with a 10K pot it's not going to have resistors in the range that go high, nor is it likely to be stressed in any way.

I would imagine that there's a preset inside somewhere that sets the neutral point, and that could be faulty - even as simply as a little dirty and noisy.

Really it depends how it's wired, and what the pot is actually doing.

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So what do you suggest I try and do?

Also, the board is soldered to the rest of the slider assembly at six points (not really a problem, its through-hole so I can resolder it right back if I take it apart) but its also held together by some sort of pins or clips that go through the pcb and sort of fish-hook into it. I can post pics for clarification if anyone needs them.

Anyone encounter something like that before? I'm not sure how to go about getting the pcb free without damaging it..

 

Do you have a circuit diagram for it?.

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Nope, no circuit diagram..sorry

 

I would use pot cleaner spray to make sure the pot is clean inside. If it's still way off, try these:

1) If you have say a 10K pot, solder a 51k aross the pot end terminals and see if the neutral moves toward center or moves farther off. If farther away:

2) Clip a trace going to the top end of the pot and solder a small series reistor, about 10% of the pot total resistance.

One of those two should move it towards center.

 

hi there,

it seems i have the same problem and found this thread through google. any updates on it? i'm not exactly much with electronics but can handle a bit of soldering

 

Since you have 2 identical turntables it should be easy to check voltage / resistance against the working turntable. The only faults that i have had to deal with in dj turntables have been drink spillage into Technics SL-1200 / SL- 1210, replace the slider pot and clean out the green furry stuff growing on the pcb. Also check for dry joints in the speed control circuit, its amazing how many faults go away when you apply flux with the magic soldering wand to joints

 

I have two faulty turntables, nothing that I can compare against.

Also, I think I'm going to take a slider apart and see if I can do anything to it, I can't find one to buy online!

 

i have the same measurements. it would seem that the fault is elsewhere. how frustrating

 

304, a slider pot wouldn't fail in such a manner, it has to be something external to the slider itself. You're really shooting in the dark if you don't have a schematic to work with or a working device to compare against.

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it now seems that this thread 3 identical turntables with the same fault, this sounds like a bad batch or a standard fault that the techs at newmark will know about, give them a call, sometimes manufactures can be helpfull.

A sneeky trick is to use one of those UV marker pens intended for marking things with your post / zip code invisibly, mark every component on the board and return it to them for repair. When it returns you can check the board under uv light to see which components they replaced.

 

Very sneaky joesoap =)

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hi, all

i've been onto numark, and they've sent me the service manual. i'm not much good with electronics, so wonder if any of you could have a look and suggest a possible source of the problem?

Download TT500_ServManual.pdf from Sendspace.com - send big files the easy way

thanks!