Korg Electribe ESX Repair - Fuse Replacement
The Symptoms
It happened to myself and I heard it from several people on the web: After a modification or just out of the blue you end up with a broken Korg Electribe ESX. The symptoms are an amber glowing LCD and tubes after power on. But you don't get any reaction on keypress and no information on the display.
What has happened?
Complex musical devices like the ESX need more than one power path to work. The Electribe has +/-12V for the tubes and audio path, +5V, +3V and +1,8V. The 1,8V path is the broken one. This voltage is needed for the digital core of the embedded microcontroller.
These voltages are generated by Low Drop Out Regulators, or just LDOs. These things just take a voltage slightly higher than the one they want to create, in case of our 1,8V you may need 2,5V. They regulate the voltage down to 1,8V and convert the remaining energy into heat.
In front of our 1,8V LDO is a fuse and this fuse has to be replaced. This is the red rectangle in the above pichture. Unfortunately these things are not huge glass tubes with a wire anymore but devices mounted on the surface of the PCB (printed circuit board) - Surface Mounted Devices, SMD.
How to fix it?
First remove all plastic knobs. Just pull on them. Unscrew all the allen keys. Remove the front. Remove four „golden" screws, not the black ones. Remove the panel holding the knobs. Your ESX should now look like on the left picture.
Now look for the region with the many capacitors. These are the big round tons. Have a look at the next picture.
There is a device marked FUSE1, marked red on the picture. On this fuse is printed a G. This is the one we are looking for, but first make sure that the fuse is really broken. You can do this by two ways:
- ESX turned off: Set your voltmeter to "Continuity test". This is often paired with "Diode Test". If you put the two tips together, it should beep. Then put one tip on one side of the fuse, the other tip on the other. If the voltmeter beeps, the fuse is intact and your problem lies elsewhere, but not in the scope of this document.
- ESX turned on: Put something not conducting below the PCB. A magazine or something similar to my mousepad in the second picture. Then turn on the ESX. Set your voltmeter to "DC Voltage". Then measure on one side of the fuse. You can get a decent ground from the black IC above and a bit left of the Fuse called "IC14". Use the big pad on the left side of the IC. If you get 3,3V on one side of the fuse and nothing on the other side, your fuse is broken. If you get 3,3V on both sides of the fuse, the fuse is intact and your problem lies elsewhere, but not in the scope of this document.
What to replace?
This is a tricky one. Yes, a wire will work. But do this only if you are in a hurry. You should replace the fuse by another one, she is there for a reason. If you want to desolder the fuse it is best to get a second soldering iron and use one on either side. If you have only one available, heat one side for 1s, then the other. Change between both sides as quick as possible while pulling on the fuse with tweezers. This needs some practice.
Because SMD are very small, they're marking is somehow cryptic. A G stands for a fuse with 0.75A. But my measurements showed, that if you stress your device, set all LEDs on etc., the current can be up to 1.7A through this fuse. So I tried a 2A fuse with no problems. I then ordered from Farnell the order number 120-6723, soldered the new fuse in and had no problems since then.
If you want to try something advanced you can have a look for a resetting polyfuse. These have a little more voltage drop than conventional fuses. But as I explained earlier, the fuse just leads to an LDO, which converts 3,3V into 1,8V. And it's kind of regardless if he creates the 1,8V from 3,3V or from 3,0V. The advantage of the polyfuse is, these things reset themselves after a while. But as I said, I haven't tried this.