Hello,
I have a Definitive Technology Supercube SC2000 which has worked flawlessly since 2015 when I purchased it. Recently, it started having a hard time powering on. By that I mean that it has no power switch, but has a circuit that monitors that line in and when a signal is present, the subwoofer is turned on. Recently, it began clicking on, then clicking an extra 2 or 3 times before it would lock in with around 1 second between clicks. Over a few weeks time this grew from 2 - 3 clicks to more like a dozen. At this point I knew I needed to do something. My first assumption was that the electrolytics had dried out. I've gone through and replaced all non-SMD electrolytics (The low level PCBA section is all SMD, all the other boards are through hole components), and did find that almost all of them were way off of their printed values. The sub no longer has a hard time starting up. One click and it's on. However, the problem I have now is that it comes on with a "Thump" where it used to start up silently. I've checked for DC offset at the speaker, and it's right around 1mv.
I've looked over the schematics (attached), but have very little experience troubleshooting to this level. I'm hoping that you guys might be able to give me suggestions as to what I should check. I don't have any experience with SMD components, and I have none in-stock, however, after watching some Youtube videos on it, I feel comfortable replacing the SMD caps if necessary. I would just need to order them. Looking at the schematics, those don't look like likely culprits to me, but I realize I could be completely wrong.
Thanks in advance for your assistance!