Bryan Ressler

Synth Stuff


HOWTO: Korg Poly-800 II Battery Replacement

Here's a tutorial on how to change the battery on a Korg Poly-800 II synthesizer. (There's also a similar HOWTO for the Korg DW-8000.) The process is complicated by the fact that the battery is soldered onto one of the PC boards inside the machine. This HOWTO will have you install a battery holder, so in 5 years when you have to do this again, it will be easier.


This procedure is not for the technically faint of heart. It requires some basic electronics skills such as soldering. If you blow it, you could kill your synth, or worse, yourself. So if you're not completely comfortable with the procedure described here, please refer this work to a professional. I am not responsible if you mess up your Poly-800 II or suddenly feel drawn to a great white light (remember: run away from the light).

What You'll Need

  • Phillips screwdriver
  • Small flathead screwdriver
  • Low-wattage soldering iron and some electronics solder
  • A low-profile 20mm single-cell (CR2032) battery holder, like Digi-Key part BH32T-C-ND
  • Ten inches of 22-gauge wire, preferably solid-conductor
  • An inch of small-diameter head-shrink tubing
  • A lighter or heatgun to shrink the tubing
  • A new CR2032 3V battery


1. Back Removal

Turn the Poly-800 II over, being sure not to put pressure on the joystick. Make sure the unit turned off, is unplugged and has no batteries installed.

Remove all 12 the screws around the periphery, and the four big machine screws on the bottom. Don't remove the rubber feet.

Tilt the bottom of the keyboard back, "hinging" it at the back edge of the unit. Here's what you'll see:

whole inside

Board KLM-1032-A (the large board on the right) has the battery right in the middle of it (round, with yellow plastic around it). Unforunately, it's soldered on, but at least it's not soldered through the board (only to the top of the board), so we can remove it while leaving the circuit board in place.

2. Old Battery Removal

battery We're going to remove the old battery by heating up the two solder points that hold the battery to the board. This must be done carefully, to avoid heating up or burning components around the battery. Don't let the barrel of your soldering iron touch any components. Be especially careful about C66, the electrolytic capacitor to the left of the top solder pad. I bent that component up to make room.

removed Put a small flathead screwdriver under the battery. You'll use the screwdriver to lift the contacts when you heat them.

Carefully heat up the top contact, while gently applying pressure to the bottom of the battery with the small screwdriver. As soon as the solder melts the contact should lift away from the board. There's no need to vacuum or wick up the solder on that contact—you'll be soldering a wire there later.

Do the same for the lower contact. The batter should come completely off the circuit board.

3. Building and Installing the Battery Holder Assembly


Get a low-profile CR2032 battery holder like the one shown here. The clip on the top is the positive side of the battery. There's not enough room inside the case for us to put the battery holder right where the solder pads are (because of the keyboard). Instead, we'll build an assembly we can put somewhere lower on the circuit board, where there's more clearance.

Solder two 5" lengths of (preferably) solid-conductor 22-guage to the two PCB lugs on the bottom of the battery holder. Once they're soldered on, put two small lengths of heat shrink around the solder joints and warm them up with the heat gun. The picture to the right shows you what it should look like.

position assembly Strip about an eighth of an inch off the other ends of the wires. Pay attention to which lead is positive. The positive lead is the one connected to the clip on the battery holder assembly. Solder that wire to the bottom solder pad on the circuit board (the one marked with the "+"). Just warm up the solder blob there, and only add solder if necessary. Now do the same for the negative lead.

Now route the wires between components and position the battery holder down lower on the board. This will keep it from colliding with the keyboard when the bottom of the unit is reinstalled. Here I planted the battery and battery holder above the 40-pin OKI part near the bottom of the board. tape

Install a new CR2032 battery. For good measure, put some electrical tape across the top of the battery holder to ensure that it doesn't ground on some part of the circuit board it will be next to.

4. Testing

Lower the back of the keyboard back down onto the front. Replace only the four big machine screws that go into the back of the keyboard assembly. Leave the screws that go into the periphery of the keyboard back out for now.

Without all the screws in it, the keyboard as a unit is not that strong, so you need to be careful here. Turn the keyboard over and place it back on its rubber feet. Plug in the keyboard's AC adapter and turn the unit on.

It might take up to 60 seconds for your Poly-800 II to stop yawning and get its act together. The keyboard doesn't have any patches in memory. It might make sound when you play the keyboard, but it's not likely to be anything pretty. But if the LEDs on the front come on, things are probably all good.

5. Buttonup

Switch the unit off and disconnect the AC adatper. Turn the unit over (again, carefully, since not all the screws are in yet). Now replace the other 12 screws around the periphery of the keyboard's back.


Now it's time to put some patches in your Poly-800 II. You can either do this by loading from tape, or by sending some MIDI SysEx. If you don't have any patches, you can get some from me.

Enjoy your improved Poly-800 II!

© 2003 Bryan K. Ressler, all rights reserved worldwide.
If you find any errors in this HOWTO, or have suggestions for improvements, please email me.