First Act MI115 LED

First Act MI115

       Recently I found a fully functioning First Act MI115 electronic drum machine in the garbage, and thought it would be a fun toy for my 2 year old daughter. Despite its (somewhat) professional look, this thing is really more of a kids toy than anything, and certainly isn't suitable for real musical work. If I had to guess, I would bet that's why this one ended up in the trash.

Whatever the reason, my daughter now had a new device to make a lot of noise with, and she was very happy. But there was a pretty big problem with the drum kit that was driving me nuts. There was no indication of whether or not the thing is turned on, and worse, pressing any button on the device (other than the pads themselves, at least) turned it on.

With this thing taking 5 AAs at a clip (and no provision for external power), the first time my daughter left it on overnight and killed the batteries, I was looking for a fix.

Looking Inside

       The idea seemed simple enough. Crack this thing open, turn it on, and poke around with my meter until I found some traces giving out 3+ volts that I could use to drive an LED mounted into the front panel.

As soon as I opened up the drum machine, I knew this was firmly in the territory of child's toy. I haven't seen internal construction this lame in a long time, it looked like a cheap piece of electronics from the 80's inside. The one thing I can say positively about the construction of this device is that they did do a pretty good job labeling traces and wires, but that isn't saying a whole lot. The mass of wires and explosion of hot glue definitely doesn't instil confidence, and I don't know how long this could last with my daughter smashing it like a lunatic everyday.

MI115 Internals
This is just terrible.

That little piece of PCB that looks like a reject from a $1 calculator is apparently the brains of the whole operation, as everything else on the board is passive. I figured this was the best place to look for a source of steady voltage that would toggle nicely with the power state of the device, so I started working my way along the edge connector that connects it to the main board. Edge Connector

Making A Connection

Luckily, it didn't take too long. The third pad from the right gave me a steady 4.5 volts when the drum was powered on, and nothing when off, and the negative line coming in from the battery compartment was right in the neighborhood.

Solder Connections

I soldered two leads onto the pads, and rummaged through my parts box until I found a suitably sized LED and a resistor close enough (around 200 Ω) to the appropriate values to keep it from exploding.

I trimmed the leads down on the LED, soldered the negative wire directly to cathode side, and put the resistor and positive wire on the anode side.

Back of LED

I found a spot on the front of the drum which had a relatively smooth backside, drilled through, then pushed the little LED assembly right in. I drilled a small enough hole so the LED fit snuggly inside, but I thought it was a good idea to judiciously apply some hot glue to the whole area to make sure it didn't work its way back out. At any rate, it matched the construction of the rest of the device.

Before reassembling the drum, I wrapped the exposed LED and resistor legs with Kapton, so they were insulated from each other and anything else that might decide to bump up against it inside of that shoddy enclosure.

Installed LED

In the end, the power LED modification worked very well. The location I drilled for the LED was a bit too close to the membrane for the keypad, which meant I had to install the LED in a slightly off-center way. The plastic also chipped a bit when I was drilling through the front panel, which I didn't expect. In hindsight I should have drilled through the back instead of the front, which would have looked a little nicer.

Of course, none of those little details mattered much to my client this time around. She was just glad to have her drum back, and I was glad to be able to tell if she had left it on after her latest impromptu jam session.

Doing a test