D-15 Distorted Audio on Both Channels

hamityanik

Hi,

I have a Sony D-15 Discman that is not working properly. It plays the CDs well, but the audio output is distorted. Both line out and headphone output is the same. I did all of these:

- Replaced all the electrolytic caps
- +6v voltage rail checked and tiny adjustment has been done

- +3.4v voltage rail was OK
- PLL Frequency was 4.3MHz which is correct

I connected my headphone directly to the DAC's output but the audio was also distorted at that point.

I checked the supply voltages of the PCM60P and the audio amp M51556, it needs to be 4.8v according to the service manual but it was about 5.8v. After that, I checked the Q301 ripple filter and base resistor which is 2.2k, and it seems also okay, but the transistor outputs 5.8v somehow instead of 4.8v. I haven't changed the transistor yet.

Unfortunately, I do not have an oscilloscope to check the voltage stability.

Do I need to change the DAC? Do you have any suggestions?

Thank you in advance!

kaosun

Repair the 4.8V power supply and replace the M51568.

hamityanik

kaosun replied at 2021-11-28 14:29
Repair the 4.8V power supply and replace the M51568.

Thank you for your answer!

Sorry, I checked the 4.8v rail again, it's 5.3v, not 5.8v. The service manual of the D-15 says it needs to be 4.8v, but on the other hand, D-25 has the same ripple filter circuit and the service manual says 5.3v. Something is not right.

I think I mixed the numbers somewhere.

Before replacing the M51568, as I said before, I connected my headphone directly to the DAC's output and I'm listening same distorted sound on that point. Do I still need to replace the M51568?

kaosun

Yes, please. The LineOUT is not supposed to be directly connected by earphone. The output impedance is 47KOHM, not the 32OHM of your earphone. If you hook an earphone, on a normal LINEOUT of a working D15, you'll hear the distortion. Again, it's normal because your wrong connection, not a circuit issue. However, the power amp of the M51568 is supposed to drive a low impedance load like your earphones.

hamityanik

Thank you!

I injected external audio into the M51568's inputs and it was perfectly fine. So I changed the PCM60P DAC to give it a try. But nothing changed. Still, the same distorted audio coming out. I think that the problem is not in the analog circuitry. I suspect it's on the digital side. What is the probability of failing CXK5816M RAM or CXD1135 DSP?

hamityanik

I changed CXK5816 RAM, still no luck. The same distorted sound.

Maybe CXD1135 DSP is the problem?

Here is the sample output by the way:
http://sndup.net/rh93

GT-R

hamityanik replied at 2022-01-12 10:16
I changed CXK5816 RAM, still no luck. The same distorted sound.

Maybe CXD1135 DSP is the problem ...

try to change dac