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Repairing a Tascam M-2524 or M-2516 – Part 4

January 20, 2018

Potentiometers

Potentiometers are tricky, because there exists many different kinds. They have a resistance value, which is the maximum resistance, and when you turn them they go down to zero. For audio applications you’ll have single pole and dual pole potentiometers, where dual pole are for stereo applications, and you can have linear, logarithmic, audio and panning taper, and they can be with or without a center detent, ie that little middle “click” so you can feel that you have put it in the center position.

In addition to that you can have different types of shafts and different lengths of shafts, and different sizes and wattages and pinouts and… yeah. It gets complicated.

For that reason, buying your potentiometer replacements from an official channel is almost always required. You have to be lucky to find the right potentiometer online, and if you need to replace several, it quickly becomes impossible.

Other circuits like resistors, transistors and electrolytes generally have less variants and it will be easier to find replacements, except for transistor types that aren’t manufactured any more.

The markings on the potentiometer is also not very helpful, but they are enough to distinguish them once you have bought the correct ones. This one says 104B, which means a 100k logarithmic. The 202H seems to be a manufacturing code. It probably tells the manufacturer where and when it was manufactured, but you would need to know how this specific manufacturer marks it’s potentiometers.

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Old

This is the new potentiometer I replaced it with. Notice that this one has the manufacturer code on top and the 104B below.

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New

As mentioned in the first blog post I won’t discuss how to solder or replace parts, there’s plenty of blogs and YouTube videos on how to do that. But use a soldering pen that has a thermostat so it doesn’t get too hot, and use tools to get the old solder away and it’s not very hard. Take it easy and be careful and you’ll be fine.

I also replaced one if the channel faders. That was very easy, because the faders are connected to the channel slider bu this blue-white-red triple connector.

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Old

So all I needed to do was to desolder it and put it on the new fader.

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New

These mixer uses ALPS faders, a very popular and famous brand, although these ones are not the professional faders they are famous for. But it still means that you can find these faders quite easily online. The service center has them as well, of course.

Assembling the mixer

Repair done, it’s now time to put the mixer back together. In general that’s just a question of putting things in the opposite order of how you took it out. Here the photos you took when disassembling comes in handy.

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How to know which screws goes in which hole.

A few steps can use some extra hints, though:

The potentiometer shafts will hit whatever your mixer is resting on (in my case a blanket, to protect the mixer from the table and the table from the mixer). So when assembling it, you will have to prop the mixer up, so that you can position the circuit boards properly.

Although the easiest way to get the channel strips in is to just put them all in, and then mount the transverse connector boards, this is not true for the output/effect/return section shown below. I tried several times, and in the end resorted to putting the whole section together as one, and then carefully putting it in place and wiggling everything to get it into the right place.

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The trickiest part

Here a phone/camera came in handy,  so I could verify that all the buttons were positioned properly.

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All in!

You also might want to put a few cables into the connectors in the output section before you flip the mixer over, as those circuit boards will fall down and land on the power supply transformer otherwise.

Once all the circuit boards are in place, it’s time to again put in the metal bar that holds everything in place, and the back plate and flip it all over. This is a good point to check that everything still works, before you put back everything on the front.

Putting back the nuts is pretty annoying, I found that the quickest way was to use a socket wrench socket (but not the wrench) of the right size, and twist it a few turns counter-clockwise to get things into the right position, and then clockwise to fasten it. Using just my fingers was uncomfortable, and using an adjustable wrench means you will scratch the front.

That’s all! Here is a closeup to see how nice and clean it looks now.

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Compare with the first picture in part 1. Quite a difference.

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I even made a dust cover.

I hope this information will help someone!

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From → electronics

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