Here are some cool links regarding synthesizers I found in the past few years:
Jim Atwood is an American living in Japan. His blog is about finding cool gear for free or insanely low prices at the local second hand stores. He reviews all this stuff on his blog. A lot of cool stories and repair tips:-)
A site with loads of information about the Roland U-20 synthesizer. Repair guides, tips & tricks, patches, you name it!:
From the same guy a site with loads of information on the Roland Super JX synthesizer:
And a great site that sells spare parts for (vintage) Rolands, Korgs and many other synthesizers:
Synths and Keyboards 