[Leo] Repairs A MIDI Sequencer

We all have that friend who brings us their sad busted electronics. In [Leo’s] case, he had a MIDI sequencer from a musician friend. It had a dead display and the manufacturer advised that a driver IC was probably bad, even sending a replacement surface mount part.

[Leo] wasn’t convinced though. He knew that people were always pushing on the switches that were mounted on the board and he speculated that it might just be a bad solder joint. As you can see in the video below, that didn’t prove out.

The next step was to fire up a hot air gun. Instead of removing the chip, he wanted to reflow the solder anyway. He was a little worried about melting the 7-segment LEDs so he built a little foil shield to protect it. That didn’t get things working, either.

Using the same hot air gun he removed the IC and then used a contact iron to clean the pads up. We couldn’t tell if he soaked his wick in flux. That always seems to help get clean wick to soak up solder better. For the soldering job, he used a smaller contact iron and very thin solder. Of course, with the hot air, he could have used paste, too.

The replaced chip looked good. Did it work? Watch the video and you’ll find out. If you like this kind of repair porn, we’ve covered a lot of interesting fixes. Check out the massive power supply repair, for example. Or the cleanup after a computer took a bath in battery guts.


7 thoughts on “[Leo] Repairs A MIDI Sequencer

    1. typically: stick the phone in a bag of rice for a week to draw the moisture out, and then give it a try.

      Some people say they wash the phone with distilled water to get rid of the impurities that might have been in the water you dunked it in.

      1. I’ve had good results by opening the phone up as far as I can, then flushing with copious amounts of deionized water (distilled will work, since DI is usually harder to find), then with a high purity isopropyl alcohol to eliminate any water that might be hiding in crevices. If you can find it, 99% or higher. My goto was 99.9%, since we had that by the drum at my last employer, and they were fine with small amounts of personal use. As long as no one went near the 99.999% purity stuff (which was kept locked up in the supply cabinet in smaller containers).

        1. Probably what I’ll have to do. It’s dry and the touch screen works, but the display is splotchy as hell. At least soak just the screen because I’m not certain how the whole phone would react to prolonged exposure. DI I believe you can get at medical supply places. Alcohol that pure would be special order. Shame I don’t have some of the cleaners we used when I worked with electronics. Laws might have changed on a few as well as pricey.

          1. I have a friend that owns an authorized repair shop. Only one in town that can fix phones on site instead of sending them in.

            First thing they tell you when dealing with water damage is DON’T put it in rice. While it will absorb some moisture it mostly just creates a bigger mess inside the phone and makes the repair harder. They usually charge more after finding rice dust.

            They then place the phone in 100% isopropyl for a couple hours. The whole thing, case, screen and all. This acts as a water displacement and is non conductive. Only then is the phone disassembled for a thorough cleaning and check for any corrosion.

    2. What we used to do with gear that had been flooded with salt brine was to wash with DI water and then put it in a vac chamber. As the pressure drops, the boiling point of water lowers and the water boils off. I have often wondered if a space saver bag with a vac cleaner would do the same thing with a phone. Haven’t tried it.

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