Korg microKorg E.2.1 Error - No Sound, Output Thumps, Service Tests Fail

Work Done So Far
Power supply recap:

• Most electrolytic capacitors replaced with equivalents, A lot were out of spec.
• Power rails now measure stable (no voltage drops noted at any ic's)

Service mode testing:

• Mode 1+3 (Auto) gives E.2.1 error (also displays Rom ver 1.03)
  

Audio behavior:
- When audio is input to [audio in jack #2] the led #6 will flicker and VR will change input level.

• No sound output from any patch, no sound from keyboard, no sound from input #2.
• Demo mode will start and switches patches 1-8 and a pop can be heard between patches. No popping from audio input.
• Previous owner mentioned: vocoder failed first, then total silence

What still needs confirmation:

Need Help Understanding where to look next? Is IC14 supposed to be ground-side control to produce the sounds since pins 2-5 have 2.5volts? I have a rigol DHO802 scope, I see a lot of activity from the DSP, I am however no expert at confirming if its sending the right data. DSP IC17 has power, ground, clock, shows communication with IC14 ((AK4522VF). DAC IC14 has power, ground and square wave on pins 10-13. Pins 2-5 have 2.5 volts. I really need help trying to pin down both the DAC and DSP, I'm thinking those are the most likely suspects, but then again it may be something else. I've attached the service manual, If anyone out there knows how to help me diagnose further, it would be greatly appreciated.

 

Korg microKorg E.2.1 Error - No Sound, Output Thumps, Service Tests Fail

Work Done So Far
Power supply recap:

• Most electrolytic capacitors replaced with equivalents, A lot were out of spec.
• Power rails now measure stable (no voltage drops noted at any ic's)

Service mode testing:

• Mode 1+3 (Auto) gives E.2.1 error (also displays Rom ver 1.03)

Audio behavior:
- When audio is input to [audio in jack #2] the led #6 will flicker and VR will change input level.

• No sound output from any patch, no sound from keyboard, no sound from input #2.
• Demo mode will start and switches patches 1-8 and a pop can be heard between patches. No popping from audio input.
• Previous owner mentioned: vocoder failed first, then total silence

What still needs confirmation:

Need Help Understanding where to look next? Is IC14 supposed to be ground-side control to produce the sounds since pins 2-5 have 2.5volts? I have a rigol DHO802 scope, I see a lot of activity from the DSP, I am however no expert at confirming if its sending the right data. DSP IC17 has power, ground, clock, shows communication with IC14 ((AK4522VF). DAC IC14 has power, ground and square wave on pins 10-13. Pins 2-5 have 2.5 volts. I really need help trying to pin down both the DAC and DSP, I'm thinking those are the most likely suspects, but then again it may be something else. I've attached the service manual, If anyone out there knows how to help me diagnose further, it would be greatly appreciated.

You might want to start by checking the output stage of the amplifier. As far as I can tell, there isn’t a full amplifier there, only the TDA1308 (see page 8 of the service manual). Check the +5V supply on pin 8 of the TDA1308 relative to ground, and make sure the "mute" signal is at logic 0. A simple test is to record a 1 kHz tone and feed it into Line IN1 to verify the TDA1308 output amplifier. Then, place the oscilloscope on capacitors C67 and C55 relative to ground — you should see a 1 kHz signal there. The entire audio path is shown on page 8 of the service manual.

 

Thank you for the reply, Input 1KHz into input 1, I see sine wave at pin 2 of AK4522VF (IC14). Input 1KHz into Line 2, I see sine Wave at pin 4 of AK4522VF (IC14). IC14 has 5Volts on pin 1 VREFH. No activity on PIN 22 &2 3 of IC14. Pin 14 of IC14 is 0volts. Pins 10-13 show square wave, which I assume is communication. C67 and C55 have 2.5Volts on positive side of capacitor. Since IC14 has no output, I'm assuming the DAC is bad? if you have any ideas where to check next? Thank you

 

Also TDA1308 IC8 & IC10, Pins 1,2,3,5,6,7 have 2.3 volts, pin 4 to ground, pin 8 5volts. This applies to both IC8 & IC10

 

You might also want to check the digital supply of the codec.
The AK4522 has separate analog and digital power domains. Since the input signal is present, the analog section seems to be working, but the DAC will not operate correctly if the digital supply is missing or unstable.
Please verify the voltage on pin 18 (DVDD).
Also, check the system reset signal. If the codec or DSP is held in reset, the DAC section will not produce any output even if clocks are present.
If the PD (power-down) pin is active low, make sure it is at a HIGH logic level during normal operation. A LOW level would keep the device in reset/power-down state.
On C67 and C55, you are seeing ~2.5V DC bias, which is normal. Make sure to check for an AC signal (1 kHz) riding on top of that DC level.

 

The AK4522 (IC14) uses three main clock signals: MCKI ≈ 12.288 MHz, SCLK ≈ 3 MHz, and LRCK = 48 kHz. These frequencies correspond to the standard operating mode at a sampling rate of 48 kHz.

 

Pin 18 of IC14 is 3.2Volt. The PD pin is 3.2Volts. C67 & c55 do no appear to have an AC signal riding on the DC level of 2.3 volts DC. Thank You for your help to this point.

 

Before concluding that the DAC is faulty, it would be important to verify the clock signals required for proper operation of the codec. Enable the frequency counter on the DHO802 scope, the signal must correspond to the frequency.


Please check the following IC14:

• Pin 17 MCKI (Master Clock) — should be around 12.288 MHz "_|‾|_|‾|_|‾|_|‾|_ "
• Pin 10 LRCK (Left/Right Clock) — around 48 kHz "____----____----____"
• Pin 11 SCLK (Bit Clock) — around 3 MHz " _|‾|_|‾|_|‾|_ "

If any of these clocks are missing or incorrect, the DAC will not produce output even if the analog input and power conditions are correct.

 

Here are the readings from pins 17, 10, 11 on IC14.

 

First, please capture the signals on pin 12 (SDTI) and pin 13 (SDTO).
Then apply a 1 kHz signal to Input 2 and capture the signals again.
We want to compare both conditions (with and without input signal) to see if there is any change in the data.
At this point, the key signals to check are SDTO and SDTI.
SDTO (ADC output): should carry digitized input signal from the codec to the DSP SDTI (DAC input): should carry processed audio data from the DSP back to the codec
Please apply a 1 kHz signal to the input and check:
SDTO — does the waveform change compared to silence? SDTI — does the waveform also change? Interpretation: If SDTO is active but SDTI is not → DSP is not sending audio back
If both are active → issue may be in the DAC section
If SDTO is not active → problem is before or inside the codec

 

SerjFixit, Excuse the delay in responding. Besides the holiday weekend I am trying to understand the what and why to the tests you are guiding me to. I want to make sure I can duplicate the results each time. Thanks for the help to this point.

 

That’s a very good question — I completely understand wanting to know the reasoning behind the tests. The idea is to follow the signal path step by step and divide the system into sections.
In this case:

• The analog input goes into the codec (ADC part) → this is checked via SDTO
• Then the DSP processes the audio data
• Then the DSP sends data back to the codec (DAC part) via SDTI

By checking SDTO and SDTI under two conditions (with and without a 1 kHz signal), we can determine:

• whether the ADC is working (SDTO should change)
• whether the DSP is processing and returning audio (SDTI should change)

This helps us isolate the problem instead of guessing whether the issue is in the codec, DSP, or elsewhere.
So the goal is not just to observe signals, but to see how the system responds to a known input.
I had a similar issue once when repairing a Yamaha P-85, so I’m following a similar diagnostic approach here. Hopefully we can track it down step by step and get yours working as well.

 

Let’s do a simple step-by-step check:

1. Set your oscilloscope ground to board ground.
2. Probe pin 12 (SDTI) and pin 13 (SDTO) IC 14 one at a time.
3. First, observe both signals with no input signal (silence).
   Take a screenshot or note how they look.
4. Then apply a 1 kHz signal to Input 2.
5. Observe the same pins again and compare with the previous condition.

What we are looking for:

• SDTO should change when the input signal is applied → this confirms the ADC path is working
• SDTI should also change → this confirms the DSP is sending audio back to the DAC

If SDTO changes but SDTI does not, the issue is likely on the DSP side.

 

That’s a very good question — I completely understand wanting to know the reasoning behind the tests. The idea is to follow the signal path step by step and divide the system into sections.
In this case:

• The analog input goes into the codec (ADC part) → this is checked via SDTO
• Then the DSP processes the audio data
• Then the DSP sends data back to the codec (DAC part) via SDTI

By checking SDTO and SDTI under two conditions (with and without a 1 kHz signal), we can determine:

• whether the ADC is working (SDTO should change)
• whether the DSP is processing and returning audio (SDTI should change)

This helps us isolate the problem instead of guessing whether the issue is in the codec, DSP, or elsewhere.
So the goal is not just to observe signals, but to see how the system responds to a known input.
I had a similar issue once when repairing a Yamaha P-85, so I’m following a similar diagnostic approach here. Hopefully we can track it down step by step and get yours working as well.

Pins 12 and 13 look similar with and without the 1khz signal. Input to #1 switch in line and mic and input to #2.

 

The AK4522 is an older codec; it does not have software control via I²C/SPI. All settings are configured through hardware pins. Therefore, based on all measurements, it is highly likely that IC14 AK4522VF is defective. Good luck!