Fixing Korg I3s


I have found that there are many users online which have this wonderful Korg Arranger. I’ve fixed one which had poor display and no sound output. I’ll list what went wrong.

#1 Fading backlight on LCD Display Screen. Although the display screen works, it can be difficult to see the text without a backlight. Firstly check that the contrast control works. Sometimes the contrast level is turned all the way up/down and you can’t see the text.

If the backlight is broken, you can replace the LCD perhaps an LED type 240×64 LCD display. You can get brandnew LCDs with LED backlights there on Aliexpress.com quite cheaply about $20 USD. You need the T6963 type LCDs. Remember also that the EL backlight on the original LCD needs about 100VAC which the internal inverter takes care of. If you are replacing it with an LED display, please use 5V ;).

#1a Unit turns on, LCD goes ‘black’ and no lights or keys / sound comes on. I have found one cause of this to be the powersupply +5V not starting up quick enough. The work around solution is to place a 10uF capacitor from RESET to Ground.

Where is the RESET pin? Fine the big D70433GD Microcontroller located on the Bottom Right of the Main Processor board.
Get the link here: http://pdf1.alldatasheet.com/datasheet-pdf/view/6999/NEC/UPD70433GD-12-5BB.html

Find Pin 8, and follow it around to the Specialised KORG MB622E 15 IC. There is a place where you can easily solder a capacitor between this RESET line and ground.

See this capacitor at the top? Add it, add it to the 5th ‘electrical via’.
IMG_1661

#2 Bad Capacitors. Does your Korg i3 smell like fish? Because if it does, corrosive electrolyte from the capacitors has leaked allover the board! Terrible! This causes tracks to be damaged and can cause open circutis and short circuits too.

Other than a visual and nasal inspection you can probably find the damaged capacitors.

#3 Still no sound? I’m not sure why but the Headphone / Line output ports of the i3 are controlled with quite a few of these NPN transistors. (Which have a non-conventional SOT23 1-B 2-C 3-E pinout, most SOT23 NPNs have 1-B, 2-E, 3-C.. but anyway) I found that these NPN are connected in common emitter mode (Emitter is tied to ground) the audio signal is passed in the Collector and the base is controlled by this ‘interesting’ circuit.

This is the mute circuit. If the mute circuit is damage the unit will always be MUTE! Again the mute circuit relies on a working capacitor, if this capacitor is dried up like most electrolytics are, then you need to replace this.

I also found that all these NPN bases are all commoned. I found the voltage base control circuit output 1.4V and all the NPNs were fully on. Hence the loss of sound (it got grounded!)

You’ll also see that there is a 1MOhm resistor pulling the base output to the -12V Rail, but it’s too weak to have any effect.

So to get sound, simply HardGround / Shortcircuit the base output to 0V. Yay the NPN’s don’t turn on and we get sound!

See that black wire at the bottom? Add it to ground somehow.. I just used the screw mount.
IMG_1662

#4 I also had an issue with the PCM69 DAC… it didn’t seem to be outputting any sound despite Digital audio data being put in. So I replaced it with a PCM1781. The PCM1781 output also has to go in after the first stage OPAMP otherwise you’ll get really bassy sound. I also noticed that at high volumes there is digital distortion which is not good. Does anyone else get this on their Korg i3 at MAX all volumes? The distortion is not related to headphone clipping as the master volume is an analogue control not a digital control like the rest.

Hopefully that helps you guys get things fixed!

Taking and putting back together a Korg I3 is really a pain as there are a lot of screws needing to be taken out. Especially with the Display you pretty much need to take it all out before being able to have access to the display module LCD.

You can also download the Korgi3 Service manual here:
KORG i3 Service Manual

Great USE!

36 thoughts on “Fixing Korg I3s

  1. Hi Adrian,

    You replied to my post on KORG Forum iSeries a while back and thank you for your time and effort. Sorry it’s taken me so long to reply.

    Your second (above) image looks like one of the two “green caps” I found inside my i3. Are they what you’re referring to? (I’m not skilled with electronics but I’m trying 🙂 If it/they are, which one and how would I ground it to a nearby screw?

    Thank you very much for your help and I look forward to hearing from you.

    Mike (Silmaril)
    makowalski@isp.com

    1. Hi Adrian,

      yesterday I fixed a problem in my i3 according to your problem #3 above. After being switched on for 1 minute or so, all outputs (line, headphone) were distorted and the signal level became very low. The problem was the electrolyte capacitor C40 (see the service manual) in the power-on mute. I changed it and everything works fine now.

      You wrote:
      “the Headphone / Line output ports of the i3 are controlled with quite a few of these NPN transistors … these NPN are connected in common emitter mode (Emitter is tied to ground) the audio signal is passed in the Collector and the base is controlled by this ‘interesting’ circuit. I didn’t bother finding out what this interesting circuit does …”

      Here are my thoughts on the function of “this intersting circuit” (the mute circuit):
      The collectors are tied to ground, not the emitters (see service manual). These 6 npn transistors are working in reverse-mode (collector and emitter exchanged). If their bases exceed 0.7V w.r.t. ground, the emitters are pulled to ground and therefore the analog signals at the emitters are grounded (=> mute). The circuit around transisor Q7 and capacitor C40 (47µF, 16V) realises the power-on mute. When switching power on, the mute signal on the collector of Q7 ( = bases of the 6 mute transistors) goes to +12V, and the analog output is forced to zero. Then the voltage on C40 increases; when it reaches ~10.5V, the mute signal goes to -12V, and the analog output is functional. The reason, why 6 transistors are used in reverse mode lies in the -12V at the 6 bases. In normal mode, the base-emitter diode breaks through at ~7V, the base-collector diode at 30-120V. So ist is safer to use the transistors in reverse mode.

      So it is not necessary to tie the 6 bases to ground; replacing C40 will fix the problem in many cases. If C40 has some leakage, it will not reach ~10.5V, the 6 transistors will not switch properly on/off and the outputs are distorted and partially muted.

      Greetings from Germany,
      Siegbert Steinlechner

    2. Grounding it to the nearby screw means connecting it to the screw hole with a conductive wire.
      Otherwise, if you have a soldering iron, remove the leaky fish smelling capacitor (smells like fish when it’s leaking) and replace it with a new capacitor of the same type.

      Or you can use the work around described above, solder a wire from the capacitor to the metal screw pad. See the picture with the black wire.

  2. Hello,

    I have a starting problem with my korg i3 for several weeks:
    – Sometimes it turns on after pressing the button
    – And sometimes it turns off after 2 or 3 hours of operation but the screen remains powered without posting!
    Korg France checked the power board and found nothing.
    For it to work I have to turn it on every day!
    Yesterday it worked several hours and then turnoff suddenly and now it will not turn on.
    Is this related : “Unit turns on, LCD goes ‘black’ and no lights or keys / sound comes on. I have found one cause of this to be the powersupply +5V not starting up quick enough. The work around solution is to place a 10uF capacitor from RESET to Ground”
    Can you help me ? ….thank you …
    JB (France)

    1. HI JB,
      Sorry it’s taken so long to get back to you. But yes, the power board is fine, it’s usually a capacitor on the main board which has dried up. It’s usually the larger, 47uF Green Colour capacitors.

  3. Boa tarde
    Ajuda para o meu Korg i30.

    Toco qualquer tecla com qualquer tipo de instrumento no i30, após retirar o dedo fica um som distorcido que logo desaparece. Já vi ligações das saídas ou possíveis fichas de contacto no interior do teclado e nada resolvi.

    Obrigado
    José (Portugal)

  4. Hi

    Can you please (Adriangin) explain how do you replaced the PCM69 with PCM 1781.

    I have also problems with korg i3 and weak volume and digital distorsion.
    I tried to do the mod from R39 to ground, but with no luck, still the sound is very very weak and it has a lack of bass. The capacitors 47uF and 220 uF seems fine, no leakage.
    Maybe they are dried out ??

    If I replace a PCM69 with a new one, will it solve the problem, or it has to be a PCM1781.

    Please help.

    Tnx

    1. Hi Sasa,
      There’s really no need to replace the PCM69 if it’s making sounds. I’d say the capacitors need replacing. Sometimes the capacitors look fine but they’re actually not, it’s best to replace them too.

      1. HI,

        I replaced the PCM69 but still the sound is distorted, no luck either with R39 to the ground.
        I will try to change the capacitor C40 and then I will let you know.
        Thanks for your answer and knowledge.

  5. Hi adriangin,

    Today i replaced the C40, turned on the i3, but remains the same.
    You can hear a sound(piano) in the bottom but over it is a nasty distorted sound like white noise. When you press the key the sound and that noise stay thill the sounds fades out.
    Before I put in the new PCM69 there wasn’t souch nasty distortion.
    Maybe I should change the PCM69 again, maybe the its faulty.
    Have you got any idea, what is producing souch a noise???
    Have you got a shmatic for conecting pins from PC1781 to the board, like pin1 to R27 and so on.
    I would try that, to save the korg.
    R39 to the ground, didn’t help in the first place.

    Please help.

    Sasa

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  7. please help my korg I2 do not have sound at all i tried R39 mod to gnd but still no sound i have replace a 6 capacitors wiht same one but sill no sound plaese help. Thank you

  8. Hi Adrian
    I replaced the backlight of my i3 with only the result of having a brighter lighting but it does not appear any writing.
    The complete display is no longer …… Is there any action I can do to revise the writing on the display?

  9. Hello: I’m trying to find a KDS 2m 25.000 It’s the 25mhz crystal for the main CPU in my Korg i3, and of course ,when it stops ‘puttin out” nothing works on keyboard- no display characters nothing.pretty sure that;s it as I’ve gone thru the i3 with my scope and have proper activity in places not dependent on this CPU working and there’s no oscillation at this crystal. It’s named “X3” on schematic, board “sx1” in parts list in service manual, and Korg’s no help. I’ve found it’s made by Daishinku, but can’t find it anywhere in their website parts listings- probably too long out of production. have email them regarding trying to get this but so far no response
    thanks ,Lee Ferreri

  10. Hi Adrian, thanks for the response.. The caps appear to be ok, the only electroytic iv changed that isnt surface mount is the large 220uf one..(i think its c39) iv tried reflowing most of the large solder pads on the pcbs and also checked the looms with a dmm..no luck!

    1. Sorry I should Mention too that this is happening on the line-outs..I dont seem to be getting any output on the headphones at all///

      1. If the unit still ‘stays’ on, does it output MIDI? It really does sound like the mute circuit is engaging… and you confirm it only happens when you put the volume higher than 2/3rds? My guess is that the higher volume results in a higher voltage which requires the mute transistors to be ‘on’ harder. Perhaps they’re not getting the right bias…

  11. Pulling the fader up theres a “wooshing” sort of sound as the fader is moved and then the output is completely cut 2/3rd through its travel… One of the first things I tried was your tip on grounding the q7 side of r39 to ground with no difference….

    1. So this 2/3rds volume cut happens on both LineOut and Headphone? You mentioned there is no output on the headphones at all. Which is it? Try run through as much of the test procedure too and see where you get. If Line Out and Headphone differ that’d be interesting as they come off the same source, it could be a clue.

  12. Hi Adrian
    My i3 has sound but has dirty noise with the patches being played. My repair tech said that the capacitors did leak. So,my repair tech replaced them. He recommended a new main board. Unfortunately, I cannot find one on the planet unless I buy a used working I3. Any words of wisdom?

  13. Caps are short for capacitors. Any good electronics store should have them. You’ll need to desolder the old caps and replace them with something of similar rating and type.

    jaycar.co.nz (NZ/AU) or maplins.co.uk (UK)

    1. Hi Adrian,
      Thanks for the Primer on caps :-). I’ll have to get myself a better solder kit and psych myself up to take on this project. Thanks for your time! -Art

  14. Korg i3 got but his dead i got nothing only black lcd
    no LED on any button no sound no sign of living but it
    has +12v -12v +5 v output at main power supply i just replaced 3 capacitor 47uf 50 v bumps and
    fuse resistor r37 r38 but still not working

  15. MY KORG I3 IS WITH AN EQUAL SOUND RADIO SOUND OF THE SEASON. BUT IF THE FX1 AND FX2 SWITCH OFF, THE SOUND IS NORMAL THROWING THESE EFFECTS. I THINK THAT IT MAY BE PROBLEM IN THE WAVE ROM LH537 AND UPD23C16000BGX. (GM2). BUT I DO NOT HAVE ANY REPLACEMENT.

  16. Hello there. My i3 (1993 version) takes a while to work after being turned on. Now after a bit of playing, the volume goes way down, comes back up, and goes down. Do you think it is the capacitor? I am just not able to get a new keyboard and am hoping to fix it.

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