Repairing a Tascam M-2524 or M-2516 – Part 2
Opening the mixer
OK, now when we have taken away all screws and nuts that keep the circuit boards in place in the front, it’s time to flip the mixer over. Careful, it’s heavy! 😉
The big silver metal sheet is what we need to remove. Which screws to unscrew is fairly obvious, but note that some of them are on the backside. However, part of the power supply is also screwed onto the bottom, and you need to remove those screws as well. The power supply is also held in place with two screws on the back of the mixer so it will not drop down, so no need to worry.
After you remove the bottom plate, you’ll notice that there is a U-bar across the mixer. This both provides some extra stability, but more importantly keeps the channel strips in place. You’ll have to remove it was well, with the remaining two screws holding it in place.
Taking things out
That’s it, the mixer is now open, and you can access the circuit boards. What you do now depends on what you need to repair. I needed to repair three of the channel strips, and one of those is channel 18, which is blocked by the power supply. So the first thing I removed was the power supply! As previously mentioned, it’s held in place by two screws on the backside, and the transformer is also held in place by two other screws.
However, those screws are not the only thing preventing you from putting the power supply to the side. No, everything inside the M-2524 is connected by soldered grounding cables. Those are the black ones you see above, and they are soldered in, and connect the three boards that form a wide band across the channel strips, and the three boards that form a thin band near the top, and the board that goes across the return and monitor section, and also the power supply. So if you want to put them aside, in a box or something, while you work on the mixer, you either have to treat them like one giant unwieldy unit or desolder some of the grounding wires. I opted for a middle ground, where I kept most circuit boards together but desoldered the grounding for the power supply. I also obviously needed to remove the cables on connector A on the power supply.
Remember to mark all cables and connectors you disconnect so you know where to connect them back. I did that by wrapping a piece of tape around the cable, and writing something on it, and putting a piece of tape by the connector on the circuit board and writing the same thing. Make up your own system that makes sense to you.
The three connecting “strips” then need to be carefully and gently removed from the channel strips. Don’t disconnect one channel strip at a time, rather gently get them off from all strips at once, bit by bit, so you don’t bend things for no reason.
The cables between the “strips” and the rest of the mixer are neatly held in place by zip ties in several places. You will have to carefully cut them off with a wire cutter.
The connecting strips are connected to each other, and with the other circuit boards with ribbon cables. You disconnect these by carefully (but rather forcefully) lifting the top part of the connector and the ribbon cable will pop out. However, try to avoid this, as you are certain to bend the wires, which makes it very fiddly to put them back correctly.
With the connecting strips and the power supply gone, the channel strips are now almost free to be removed. But just almost. The little tongue on the microphone input will get stuck in the hole. To remove the channel strip you need to reach under the mixer and press the tongue upwards while carefully maneuvering the channel strip free.
I started with channel strip 5 as this is the one with the bent potentiometer, one of those I needed to replace. I later removed all strips to better clean the front, but I had not made my mind up about that at this point, but I later decided to remove all the channels to clean the mixer front properly.
Afterwards I removed the board that covers the return and monitor boards. It’s the same here, removed it gently bit by bit from all boards at the same time.
Once that board is gone you can remove the underlying boards. However, some of them are attached to the front with little plastic “rivets” that needs removing. That is also fiddly.
To start with you need a small screwdriver to push the plastic “pin” down and reach under the mixer to pull the pin all out. It may fall out completely, so be careful that it doesn’t disappear. Then you press firmly but gently inwards and downwards on the remaining “neck” that sticks up, while you pull on the circuit board.
The transformer is easily removed by removing the two screws on the mixer backside that holds it there, and two screw that holds it into the metal “box” that surrounds the digital circuitry and the meters. One of those screws also holds a piece of wire that holds a few cables in place. It’s probably not important, but try not to lose it.
The power cable is also “hooked” into the chassis, but you can just unhook it easily.
Underneath the transformer, you find a piece of shielding attached with a screw. Underneath that is the input/output boards, which if you unscrewed them now can be just lifted out. There’s also a piece of shielding between two of the boards. If you don’t have the service manual you need to keep track of where it should go, by taking a photo or something.
I let the volume meters and the digital circuit board stay in the chassis because they are flat enough to easily clean the front anyway, so I didn’t need to. I also didn’t disconnect the input/output boards above, I instead lifted them a bit and then taped them in place so I could flip the mixer over without them falling out.
I also unscrewed one of the faders, as the knob was loose. They are simply attached with two screws from the front, nothing strange.
Next part I’ll discuss the cleaning a bit.