Thanks for the input! I picked up this keyboard at a flea market, so I'm not sure how or when this issue came up. This model (iS50) doesn't have an audio input—only the iS40 does—so those dotted lines in the schematic don't really apply to me. And yeah, both the left and right channels are definitely the same volume. I'll check the voltages again while I'm waiting for my ESR meter to arrive.
As for Q7 and the mute circuit: when I tested that transistor, it showed some weird values compared to Q1-Q6 (which are NPN), so I took it out to see what would happen. But the problem still happened,...
chinhang899
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Last Activity: 04-28-2025, 05:33 AM
Joined: 01-04-2019
Location: Hong Kong
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KORG Piano Keyboard: Low Phones/Line Out help
Hey everyone!
My KORG iS50 has a volume issue where the internal speakers are only acceptable above ~50% on the master slider. What's worse is that the headphone (phones out) and line outputs are extremely quiet, even at max volume. Both left and right channels are equally affected.
Here's what I've checked:
Voltages: Vcc to DAC section measures ~5V, MUSB (mute pin on the DAC) measures ~4.xxv, and the 2 op-amps show ~9V
Master Volume Slider: Resistance ranges from single-digit Ω to ~11kΩ (seems functional).
Visual Inspection: Capacitors on the main/speaker...
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