Korg Synthesizer/Vocoder -schematic?

[mdxeng]

Korg Synthesizer/Vocoder -Does anybody have a schematic? I have one of these which doesn't power up correctly and I suspect a problem in the power supply.

[Enzo]

Here


Also this bulletin:

microKORG power problems
Problem
The microKORG does not start after switching the power on. The audio Audio Input LEDs may light up briefly on power-up.

Solution
The symptoms above are usually caused by damage to the power supply circuit. The following components should be checked and/or replaced.

Location Description Part #
FU1 Surface mount fuse CCP2E20 184090000
IC5 IC-S-8520F33MC-BNS-T2(TS) 324023008
F1 FET CPH6302 304060250
* IC18 CPU HD6412320VF25 320004686

After repair, check the voltage at FU1. It should be approximately 3.3 volts. If it is closer to 5 volts then replace capacitor C31 (100uf 10V)

* Update! Since this bulletin was first written we have heard of some units where the CPU (part # 320004686) was damaged along with the power supply components. It is recommended that you replace the CPU as part of the repair. If you do not have the equipment to change larger SMT ICs like the CPU you should order a complete main board (part # 001233300) instead of replacing the components listed above.




And this one as well:

microKORG
Preload
Hold down the [WRITE] and program [5] buttons while powering on the unit.

Display ROM Version
Hold down the [WRITE] and Program [6] buttons while powering on the unit.

Wheel Calibration
Hold down the [WRITE] and program [7] buttons while powering on the unit.

Diagnostic Test

Setup
Connect the microKorg's MIDI In and Out jacks with a MIDI cable.
Connect the output jacks to an oscilloscope.
Turn the Master Volume Control up to max.
Procedure
Hold down the [WRITE] and program [1] buttons while powering on the unit.
The display will cycle through some numbers, a blank screen, and will finally end up will all the LEDs lit. This takes about 15 seconds.
At this point a clean undistorted sine wave should be coming out of each output jack. This wave should remain undistorted even with the microKorg volume set at max.
Press the Program [8] button. The LED display will cycle through all it's segments.
Press the Program [8] button again. The LED will display "3.01" and the "TEMPO" LED will be lit. This is the start of the button test. The buttons are tested from left to right starting with the Arpeggiator [ON/OFF] button
Press the Arpeggiator [ON/OFF] button twice.
Press the [SIDE] button 3 times. Each press will toggle the LED underneath the button.
Press [WRITE].
Press [SHIFT].
Press the [TIMBRE SELECT / FORMANT HOLD] button 7 times. Note that a different LED lights each time.
Press all the buttons on the bottom row once. Starting from from the [UP] button and ending at the Program Number [8] button.A red LED under each button indicates when it should be pressed.
At this point the display will read "P.SL" This is the start of the rotary knob tests. The display will indicate which knob to test, and the Octave Shift [UP] and [DOWN] buttons indicate which direction to turn the knob. If the [UP] LED is lit turn the knob clockwise. Turn it counter-clockwise if the [DOWN] LED is lit.
"P.SL" indicates that the Program Select knob is being tested. Rotate this knob in the direction indicated by the Octave Shift buttons. After each successful knob test the display will indicate the next knob to check.
Once you have checked all the knobs, the display will read "bnd". Move the pitch bend wheel all the way up and then all the way down. Release it and press [8].
The display will read "nod". Turn the mod wheel up and the down. Press [8] The display will briefly display "urt" as the wheel data is written to memory.
The display will now show "Hi". Press [UP] to skip this test.
The display now read "C 6". This is the keybed test. Play each key from right to left.
When the keybed test is complete the display will read "PLD". Press [8] to load the preload data and return to normal mode.
Proceed to the Audio Pass Through test
Audio Pass Through Test

Setup
Turn the Audio In 1 and Audio In 2 volume controls on the rear of the unit up to max.
Set the Mic/Line switch to Line.
Connect the output jacks to an oscilloscope.
Turn the Master Volume Control up to max.
Procedure
Hold down the [WRITE] and program [8] buttons while powering on the unit. The display will read "Aud".
Input a -4dBm 1KHz sine wave to Input 1 and check that a clean undistorted sine wave comes out of the Left/Mono output.
Input a -4dBm 1KHz sine wave to Input 2 and check that a clean undistorted sine wave comes out of the Right output.
Set the Mic/Line switch to Mic.
Input a -30dBm 1KHz sine wave to Input 1 and check that a clean undistorted sine wave comes out of the Left/Mono output.
Press [8] to return to normal mode.

[Matt Michel]

I also have a microkorg and when I power up it won't do any self-tests it just flashes lights underneath the buttons, numeric display looks like garbage and no sound in the output. Can anyone recommend a fix?

[Enzo]

Have you followed the steps in the above posted bulletins? Have you downloaded the servicemanual and done the diagnostics? And have you reinitialized the unit?

[Matt Michel]

I have measured the voltage at the FU1 and it measures 3.3 VDC with batteries inside. I did however look at the Wall wart power supply and it measured 14 VDC by itself. I wonder if this was the culprit. I tried both your Diagnostic Test and last setup and I get the same problem when I power on just flashing lights with no sine wave in the output.

How do I reinitialize the unit?

Thank you,
Matt

[Enzo]

Well, this wouldn't be my strong suit, but I would be looking at the schematic and exploring all the power supply voltages. The 3.3v is for the processor, but is there not also +5? Not to mention the analog voltages.

Reinitialize is the same thing as "restore factory settings" so if you see that, that is it. I think the "preload" thing above might be that.

[Mars Amp Repair]

I've see where these can have just the 3.3v supply bad including the switching coil in there AND the shorted processor, too. .it's probably a good idea esp if you're repairing this for a customer to first try & substitute the 3.3V in from an externally regulated source to determine if the processor is also bad.

The processor is only about $15.00 but it is surface mount so you have to be capable of replacing that. glen

Here is the bulletin:
Solution

The symptoms above are usually caused by damage to the power supply circuit. The following components should be checked and/or replaced.
Location Description Part #
FU1 Surface mount fuse CCP2E20 184090000
IC5 IC-S-8520F33MC-BNS-T2(TS) 324023008
F1 FET CPH6302 304060250
* IC18 CPU HD6412320VF25 320004686

After repair, check the voltage at FU1. It should be approximately 3.3 volts. If it is closer to 5 volts then replace capacitor C31 (100uf 10V)

* Update! Since this bulletin was first written we have heard of some units where the CPU (part # 320004686) was damaged along with the power supply components. It is recommended that you replace the CPU as part of the repair. If you do not have the equipment to change larger SMT ICs like the CPU you should order a complete main board (part # 001233300) instead of replacing the components listed above.

[stef]

Hi,

if i may add a question - i have a ESX1, seems to have the same problem regading the 3.3V power at FU1. I measure without any load on FU1 and GND over 13 Volts. Thank god it powers up with an external PSU at 3.3 Volts and AC9V for the other components. No matter on which pin i measue on the 6302 or 8520, i get every time 13 Volts (except Component-GND, of course). Obtaining these two parts on Germany is quite impossbile and i don t find any resources. Could it be an option to "override" these two parts with a component like a LM3940?

Many thanks!

[analog101]

same problem

Hi my IC5 is burn. where can i buy
FU1 Surface mount fuse CCP2E20 184090000
IC5 IC-S-8520F33MC-BNS-T2(TS) 324023008
F1 FET CPH6302 304060250
* IC18 CPU HD6412320VF25 320004686


Many thamks!