Fixed my Sennheiser HD650's!

So, about a year ago, my Sennheiser HD650's started developing a problem with the right channel; the volume was lower than the left and the bass was weak. Ever since I bought the headphones back in 2007 (used off eBay), the right channel was always slightly lower than the left, but the problem became more noticeable as time went on. Since I had my HD800's to use as my main headphones, I just put the HD650's on a shelf and left them there for over a year.

The other night, I was looking for a part for my computer and came across the headphones. I had my digital meter nearby, so I thought I'd test each drivers impedance since the problem could be a shorted voice coil. Both channels measured exactly 315 ohms, so that couldn't be the problem. That got me interested to dig a little deeper why the right channel had issues. 

The HD650's are a very modular design and easy to take apart. The first thing I did was pull off the soft ear cushions and foam cover. I spotted something that didn't look right - the left channel driver cone was about 1/8 of an inch away from the grill and on the right channel, the cone was sunken in almost a 1/2 inch! I carefully removed the back cover of the ear cup off and there it was - the driver assembly wasn't fully pushing in and locked into place! There are four clips that hold the driver and cable connector in place and only was holding it in. So, I pushed the driver assembly back down until all four clips were in place; replaced the cover and re-assembled the headphones...

It worked! Both sides were now perfectly even in volume and the bass was back, good as new! Maybe the driver came loose during shipping or the previous owner dropped them - pushing the driver back in fixed the problem. 

So, if you have a pair of HD600/650's and one of the channels seems lower in volume than the other (or lacks bass), check the speaker drivers and make sure they are fully clipped in. My 650's sound better than I remember when I first got them - with deeper bass and pinpoint imaging. 

I attached some pictures of the repair: