LUXMAN D-105U CD PLAYER DISTORTED AUDIO FAULT

[GJW]

Hi. I am in need of help to find the cause of very distorted sound output from my player. I have a schematic but insufficient skill to track the fault. The distortion is from all outputs including headphones. I have made some checks and found that the sound input from the main board to the tubes was fine. I connected an amp to this point and the sound was perfect. The distortion seemed to be after the tubes. However when I substituted the main board with one out of another 105u with a faulty laser, the fault disappeared. This made me suspect that the issue was in the output stage of the main board and not the tube output section at all. It is possible that the audio signal to the tubes is too high and driving the tubes to distort. I could have fixed the problem by leaving the spare board in place but during some further check I plugged a lead from the laser unit into the wrong socket and destroyed something on the board. So now I am back to tracking the fault in the original board. I understand that this is not a highly regarded player, however, I would like to repair it and keep it with my collection of cd players.

Grateful to hear from anyone who can assist me in locating the cause of the distortion.

GJW

 

[djmiddelkoop]

GJW,

the tubes are used as buffers, so there is not much that can go wrong if both the heater and B+ voltage is present.
Also the tubes used, usually GE 6CG7, are very reliable.
What you should check first is all the solder joints involved, resolder every joint that looks suspicious.

Dick

 

[georgehifi]

GJW,

the tubes are used as buffers, so there is not much that can go wrong if both the heater and B+ voltage is present.
Also the tubes used, usually GE 6CG7, are very reliable.
What you should check first is all the solder joints involved, resolder every joint that looks suspicious.

Dick

The output stage is solid state IC M5238 after the tubes on the variable output.
The fixed ouput comes from the tubes, if the fixed output is distorting and your sure the tubes are working fine, then it could only be the muting transistors.

 

[GJW]

Thanks to both of you for responding. I have checked all the solder joints and they seem fine. The reason I think the fault is in the main board is because when i connected an external amp at the input to the Tube 2 PC Board at CH 401 L & R channels there was no distortion from the external amp but there was distortion at the fixed, variable and headphone outputs. However, when I substituted the main board with one from the other player, the fault was not there. I can only deduce from this that the sections after the Tube 2 Board audio inputs and the Power supply are ok. I do find this very odd as there is definitely no distortion before the Tube 2 PC Board on either of the main boards. I think I destroyed the motor driver IC 204 STA341M on the good main board when i plugged the leads into the wrong sockets so if I cannot find the fault, I will see if I can repair the board that worked fine. Could it be that the audio signal from the original board is too high and driving the tubes too much.

 

[georgehifi]

See if there is any dc offset at left and right channel pins 5 & 3 on connector block CH402 if there is dc offset then the electrolytic coupling caps going back to the tubes are shot.

Cheers George

 

[GJW]

Thanks George. I did not change any other boards and there were no issues when the substituted main board was fitted. Thats why I am sure the problem is caused by something in the main board. However, I will check for DC offset. Just in case I cannot located the problem, I ordered a couple of new IC 204s from WES yesterday. May be able to fix the main board if I didn't destroy anything else. Can I phone to discuss; it might be easier.

Regards, Greg