Reparing a Yamaha NP12
No sound on a Yamaha NP12
Introduction
The Yamaha NP12 piano is part of the Piaggero series. It uses a lightweight 61-key keyboard; the architecture is identical to the NP32 (76 keys). Fortunately, the service manual is available, as well as the datasheets for some key components.
Analysis
The symptom is obvious: no sound at all.
Going up the audio chain, it's easy to see that nothing is coming out of the stereo DAC, an AK4430ET from Asahi Kasei. The DAC-L and DAC-R test points remain at 0V.
As a first tentative to fix the issue, the DAC has been replaced, without success. I also replaced C363, a capacitor that serves as a charge pump for the DAC: no change.
Then I went into a deeper analysis, focusing mostly on the DAC
Power supply
All the DAC supply voltages are compliant with the datasheet:
On input:
- VDD = CVDD = 3.3V
- VSS1 = 2mV
- VSS2 = 7mV
- VREFH = 3.3V
- VEE = 880mV (this value may be a bit high)
Digital signals
I checked the digital input signals: they all seem normal.
The VH and VL values are 3.3V and 0V respectively, so they are compliant.
The clocks are:
- MCLK = 11.3 MHz and LRCK = fsd = 44.2 KHz, which is consistent with the datasheet (256fs = double sampling speed).
- BICK = 2.82 MHz which corresponds to 64 * fsd (double speed mode).
DIF is HIGH = I2S protocol is being used.
The signal on SDTI follows the key presses on the keyboard; by observing the "communication density," you can clearly see the attack and release of the sound.
Since the SMUTE (Soft Mute) pin is used to disable the AOUTL and AOUTR outputs, it's logical to check the voltage at this pin; we find 146mV. This pin is driven by transistor TR361 (a DTC023J from ROHM). By shorting pins 2 and 3 of TR361, we lower SMUTE to 0V, but no improvement in behavior is observed; we can therefore consider the signal to be low (L), meaning the outputs are indeed enabled.
Next step
My guess is the new DAC could be a fake; the reputation of vendor is pretty low. So I decided to get a DAC from another source.
More to follow.
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