Hi, After replacing a completely shot volume pot on my WM-7, I noticed Dolby NR is not working. The switch doesn't change anything and it's not the switch's fault. I know this model uses a DC-DC converter for the Dolby NR, would this mean the converter is shot?
Hi, I had the exact same problem on my WM-7. I first suspected the DC-DC converter, but I tested it and it worked fine. The problem are the 2 potted hybrid modules (CP101 and CP201). In my case, the Dolby worked at first and then developed a cracking sound and stopped working after a few minutes of play. It would sometimes work again when I let the walkman sit a couple of hours, but only for a couple of minutes. I suspected the hybrid modules because this is a known problem in other SONY walkmans such as the WM-D6 and D6C (the EQ and mute modules). At first, I was determined to make some custom new modules with SMD components, but I found that they can be repaired quite easily. The potting compund becomes conductive and that causes the problem. All that is needed is depotting the modules. You need to put them in acetone for a couple of days and then the potting compound will become like rubber and you can easily scrape it with a pair of tweezers. Anyway, after depotting them, I decided that this was the better solution, since there probably wouldn't be so much demand for new modules. Please let me know if I am wrong, as I already desined the PCB, but did not got it manufactured. I did this a couple of month ago and Dolby still works fine today. You could measure the output of the DC-DC converter, it should be around 12V, depending on the load. But I am pretty confindent that the CP101 and CP201 are the culprits in this case. And like in the WM-D6C, they will eventually fail, even if they didn't yet (I'm writing this for other people who might read this). EDIT: Since I posted this, I performed the depotting successfully on other WM-7s and mine is working just fine.
