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Need help to low volume issue of Korg SP-200

ipsych

New Member

C0990631-92FD-4F1B-8B79-89B50679648D.jpeg

The korg SP-200 shows very small volume.
I replaced 4556AD and 33078P in orange board, and POM1716E in green mainboard, volume switch in control board (impedance is OK).

Intereting part is small volume is same for midi output. So I am suspicious some smd capacitor or main chip in green board.

Does anybody tested and successfully repaired similar problem?
 

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rjenkinsgb

Well-Known Member
Most Helpful Member
It is likely either a power supply or mute control problem somewhere - or a corrupted parameter?
Have you done a "Factory reset" on it, to ensure it's not something messed up in its settings?

Check the "Mute" circuit - in the right hand side of the output board diagram on page 14 of the service manual.

If the 12V supply is too low or something has failed in that area, it will be turning on several transistors that short out the audio signal, to prevent unwanted noises as it switches on or off.

Check the voltage on R3 / R4 / R10 / R11. Those should be near 0V when it's supposed to be working normally. 0.6V or higher means the mute circuit is active, killing the audio.

With adequate power, TR6 should be on, pulling R12 low and turning off the digital transistor (a transistor with a built-in series resistor to the base & a base-emitter resistor. Everything from the output of TR7 to the base of TR5 should be close to 9V.

I've grabbed the relevant part of the diagram, below.


Other than that, the two channels are totally separate from the DAC through to the output sockets. See IC10 on the main board (DAC) then IC11, the first audio stage.

Full service manual here, if you do not have it:

KorkMute.jpg
 

ipsych

New Member
It is likely either a power supply or mute control problem somewhere - or a corrupted parameter?
Have you done a "Factory reset" on it, to ensure it's not something messed up in its settings?

Check the "Mute" circuit - in the right hand side of the output board diagram on page 14 of the service manual.

If the 12V supply is too low or something has failed in that area, it will be turning on several transistors that short out the audio signal, to prevent unwanted noises as it switches on or off.

Check the voltage on R3 / R4 / R10 / R11. Those should be near 0V when it's supposed to be working normally. 0.6V or higher means the mute circuit is active, killing the audio.

With adequate power, TR6 should be on, pulling R12 low and turning off the digital transistor (a transistor with a built-in series resistor to the base & a base-emitter resistor. Everything from the output of TR7 to the base of TR5 should be close to 9V.

I've grabbed the relevant part of the diagram, below.


Other than that, the two channels are totally separate from the DAC through to the output sockets. See IC10 on the main board (DAC) then IC11, the first audio stage.

Full service manual here, if you do not have it:
Thanks. How can I 'factory reset' the SP-200?
What I found in google is below. is it right?

press knob 1 and 2 and rec at the same time , then power on , then knob bank D , power off and on ,,,,, ready
 

rjenkinsgb

Well-Known Member
Most Helpful Member
What I found in google is below. is it right?

press knob 1 and 2 and rec at the same time , then power on , then knob bank D , power off and on ,,,,, ready
That's the only sequence I can see, as well - I cannot find anything in either the user manual or service manual.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
OK..

Have you checked the voltage through the "mute" circuit? eg. the voltage on the collectors of TR6 and TR5, to the 0V/GND ?
 

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