Need help to Repair Korg SP-200 Low volume problem

[ipsych]

The Korg SP-200 plays very low volume.
My symptom is interesting because, the same issue happens both headphone and MIDI to Mac.
(In Mac, make mac volume max, and the midi interface amplification max, it's somewhere in 'mid-range volume).
First I checked below two posts, and replaced 4556AD and 33078P in orange board, and POM1716E in green mainboard, volume switch in control board (impedance is OK).
https://www.electronicspoint.com/forums/threads/korg-sp-200-piano-low-volume.293013/

https://www.electro-tech-online.com...r-repairing-soft-volume-in-korg-piano.157969/

I guess the issue is in mainboard (Since all capacitors are intact in orange board, and replaced all AD converter in the same board), and trying to replicate electro-tech-online post, but cannot point out which SMD cap should be replaced.

I believe many SP-200, 250, 300 users experienced same issue with different cause.
Any help would be very appreciated. Thanks.

 

[Harald Kapp]

the same issue happens both headphone and MIDI to Mac.

MIDI is a digital interface. No actual sound is transferred but digital info on which tones to play. Therefore any issue with the analog signal chain should not be present over MIDI.
If you have the volume issue over MIDI, it is probably a setting, not an electrical issue, that reduces volume both in the analog signal chain and the MIDI

 

[ipsych]

MIDI is a digital interface. No actual sound is transferred but digital info on which tones to play. Therefore any issue with the analog signal chain should not be present over MIDI.
If you have the volume issue over MIDI, it is probably a setting, not an electrical issue, that reduces volume both in the analog signal chain and the MIDI

Than possibly the cold solder joint or other problem in volume controller in panal board might the issue?

 

[Harald Kapp]

A cold solder joint, a defect in the potentiometer, a defect in the ADC that converts the potentiometer output voltage to a digital signal indicating the volume, a defect in the supply voltage of the potentiometer ...
Inspect the solder joints visually, re-solder suspect ones. Check the function of the potentiometer. Measure the voltage across the potentiometer and from teh wiper of the potentiometer to ground.
Check the correct seat of all connectors.
Check any setting that may influence the volume.

 

[73's de Edd]

Sir ipsych . . . . .

If the master vol board is cleared of suspicion, you need to move on to the main board next, where the IC10 D-A converter regurgitates the processed digital info into being R & L analog audio again..
Take in hand a 10 uf @ 16-25 dc rating and solder tack two insulated wires ~6in long so that you now have a cap with " two test leads " and their companion " end test probes " are then being the just barely exposed bare wire tips at the wires other ends.
Get the unit making a note / noise and evaluate its max audio output level.
Then OBSERVE your choice of either electrolytic can C8 or C18's polarity and put your test capacitors two leads PROPERLY across the one you chose.
Any volume increase ? . . .if so test the other cap in the same manner . . . . thereby, testing both R & L channels in that manner
Additionally there is being a bypass function associated with circuitrry within the innards of the IC10 chip needed for either channel . . . . use the same procedure across C14 and C15, to see what further volume level improvement might be acquired with their replacement additionally.

BUT I'VE NEVER DONE NEURO-CORTEX SURGERY BEFORE . . . . . .

Not to worry, if needing to replace . . .just use conventional radial lead E-caps with leads cut off to a 1/2 in length and form right angle wire feet at their ends .
Play with the spacing until they conform with the solder pads to be resoldered onto.

NOW . . . . .
If being a novice at the removal the type of cap you see being used . . .take no chances for board foil damage .
Note that almost at its base that there is an imbedded annular ring that encircles the unit, take a pair of diagonal cutters and lock their cutting jaws into that rings depression.
Then you clamp down and clip into as much of the cap as you can . . .it may take 3 clips to work your way all across it and have its top pop up and off.
That then leaves you with a small aluminum ring which you come down on from the top and clip on one side, so that the ring can then be spread wider and will peel off. Then clip away all of the small amount of a slug of cap innards, til only its two vertical wire leads show.

They should be passing thru two holes in a black round plastic / fiberboard disk. Pry that up and lift off and you should then have just those two leads soldered to their PCB solder pads. Take tweezers and desolder those two old cap leads snippets.

THE INSTALL . . . . .
Prep your new caps, small right angle feet to mate up with those pads.
Fresh solder tin the old pads and the new feet leads.
Figure the best angle to come in with your soldering iron tip with minimal chance of collaterally burning anything in the install procedure.
Take the opposite position of the soldering irons entry point and tilt back your caps body 45 degrees to thereby give you even more iron tip access.
Line up the wire feet to the pads and reflow solder. Let the joint COOL . . . . move the leaning cap body up to the vertical from its leaned over position.
Onward to other caps . . . . .

RELATED SIGNIFICANT TECHNICAL INFO . . . . .

Thaaaaaaaaasssit . . . . .

73's de Edd . . . . .


The Dead Cat
A kindergarten pupil told his teacher he'd found a cat.

She asked if it was dead or alive. "Dead," she was informed.
"How do you know?" she asked.

"Because I pissed in his ear and it didn't move," said the child innocently.

"You did WHAT?!" . . . the teacher laughingly shrieked in surprise.

"You know," . . . . . the boy then explained more fully . . . . "I leaned over and
loudly went 'PSSSSSSSSSSTTTT . . . in its ear, and even then, it wouldn't
move at all."


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