Sony D311 volume always high

m_saborio

Hello Mr. Kaosun!

The problem I am having is that it is not possible to reduce the volume of the headphone out. Turning the volume potentiometer all the way down decreases the volume of the headphone out only slightly. I have already replaced all SMD caps. All were damaged, but the leakage was contained to the pads of the capacitors and the pads are in goodh shape. I checked for damages to the traces, and they all seem to be healthy.

I was able to solve the issue for a while. I moved the potentiometer up and down a few times, and the volume started working, but the audio cracked a little. It seemed like a dirty potentiometer. So I soaked the potentiometer with IPA (while still soldered to the PCB), moved the potentiometer a few times more, and the problem seemed to be solved. The volume was working and I was able to turn it all the way down without distortions. Two hours later however the issue reapered. Soaking the potentiometer in IPA did not solve the issue this time.

Funilly, I also have a D211 which has exactly the same issue. With the D211 I also replaced all caps, checked the traces and even checked all the voltages on the DAC and muting circuits. Given that the D311 and D211 have an identical audio amp circuit (all the componentes from volume potentiometer to the headphone jack are identical), I ask myself if both are affected by the same problem.

For both players I also measured the resistance values of the potentiometer, but I am not sure if the readings are ok:
- Ground to potentiometer inputs: 8.25 kOhms / 9.09 kOhms (aproximate, slight variations from one player to the other)
- Between potentiometer inputs: ~17 kOhms
- Moving the wiper from one end to the other changes the resistance at the wipers from 0.03 kOkms to ~17 kOhms

In case of the D211, I also disassembled the potentiometer and checked for corrosion, but I found no problems. I also checked the voltages at the amp pins. They all matched the values on the service manual (1.2 V for the amp inputs and outputs, 1.2V for the reference, 4.5V for supply).

Any idea what could be causing the problem. I am not sure if the root cause is the same in both players, but given that the line out is ok, and that both players share the same electronics for the amp, it might well be that both are suffering the same issue.

Any help or advice is appreciated.