I am currently working on the D6C I purchased a few months back. It is a first revision phenolic board D6C.

I have solved the biasing and headphone playback level issues that it had. It turned out to be the Headphone amps IC202 and IC102. I replaced them both with identical ICs from my parts unit.

However, a new problem has cropped up.

During recording in Type I mode only, crackling can be heard in the right channel on playback of the recording (cannot be heard when monitoring the recording).

After a few minutes, this crackling becomes louder and eventually becomes white noise. During this, the music can still be heard in the background.

I've dived into the service manual and have ruled out switches and pots.

I believe the problem area lies somewhere around C245, a mylar cap, as shown in the diagram below.

As this only happens when recording in Type I mode, I believe it may be caused by either: the transistor on Pin 5 of CP302, which seems to do switching for the Right channel for Type I and II when recording, C245 and R261, which comes immediately after and leads to L201. Since L201 is shared by both TYPE II and Metal modes, it can be ruled out. C245 is a mylar cap 0.01MF and R261 is a resistor.

I'm suspecting the Mylar Cap.

Can any experts weigh in on this? Or anybody experienced something similar before?

Happens on any power supply. What is the Serial No. of your D6C and does your crackling happen on a single channel or both? Does it happen when recording on different tape type settings?

So far I have only perform recording on normal bias. But I will check out the serial number and let you know soon coz I'm working abroad and be back home during weekend. Btw I found this forum on Tape Heads which I believe could give us some clues to the problem.

http://www.tapeheads.net/showthread.php?t=19420

I have a Bx-125 too. The BX-125, a 2 Head unit, is similar to the D6C in that it has a REC/PLAYBACK switch. I also encountered crackling on all recording circumstances on my BX-125, which was fixed by cleaning the relay with deoxit.

I suspected this to be the cause first, so I opened up the switch in the D6C and cleaned it as well, and even swapped it with a good one from a newer D6C. In my case the pots and switches can be ruled out.

Some Naks also suffer from orange cap disease which can cause crackling as well.

I'm hoping my D6C's problem lies in a mylar cap or something easy to replace, and not a unique self contained unit like CP302. 

This is the serial number of my D6C, the crackling happen on a single channel and usually started with soft and gradually became louder and louder and then it goes off again. It doesn't happen on the entire recording.

My low serial 30k D6C has developed exactly the same problem. Only with type 2 recordings.

Finally got around to attempting to fix this. Sadly neither C245 or R261 is at fault. This leads me to believe that a transistor in CP302 is at fault, which is difficult to find a replacement.

In the meantime, I've taken my other newer serial D6C with a worn permalloy head apart to swap the boards. I hope that it will be easier to adjust the settings of the newer board to match the older amorphous head than it is to troubleshoot this board any further.

Hi Bub,

Did you manage to confirmed the rootcause for this phenomenon? I also experience the same problem with my D6, the crackling usually happen later in the recording maybe the transistor heat up and that's when it start to show the problem.

Actually, I did in a way. It was quite a while back, but if I remember correctly what I did was swap CP302 with CP303 so that the transistor's duties where rearranged. The damaged transistor in CP302 would end up doing a job not integral to the TYPEI/II REC sound path. I figured it may end up affecting the METAL REC position instead, but the problem never popped out again. It's been making great TYPE I/II recordings since then. I'll need to try METAL REC again to verify.

I have no idea if this was an actual fix or the solder reflow solved the problem. I did not swap the boards in the end.

I just did a 45 min METAL REC test, no crackling. I think that since it's 2 years since I made the repair, swapping the 2 transistor packages somehow solved it for me.

Great Bub, long live the Sony WM-D6. In fact no portable recording device can even come close, it's indeed our responsible to upkeep and sustain its condition so that it could last forever. 

Hi Bub, almost certain to your problem is due to dry solder joints as what you claimed. This article is sure helpful..

http://sound.westhost.com/troubleshooting.htm#s11