It is quite uncommon for musicians to do stuff like this, but with Nurkostam everything is possible. We bought our first mellotron, a white EMI-made M400 from Portugal via eBay, knowing it wouldn't be in a good shape and that it needed some work:
Well, it sure needed some work since it really didn't produce any sound. The first step in restoration was to call to a local analog god named Nuuska, who has worked at Studer and basically knows everything about these kind of things. First aid was to install an old pre-amplifier card from a Studer tape recorder, after this we finally had a sound! Still, playing touch was horrible and the whole thing was out of tune.
We knew that we would have problems with this particular M400, since it was EMI made. The previous owner had also modified a weird window on the top panel along with the power light, which can be seen in the photo above. It also had the CMC-10, maybe the worst motor control circuit one can have in a mellotron. Up untill today Nurkostam was putting up with this thing, an unreliable mello that could be out of tune anytime and usually was. Then, I took the initiative to buy a new motor control circuit from www.mellotron.com:
After carefully following the instructions I finished the upgrade. The very annoying audio whine is now gone, the whole thing is more in tune than ever, overall our mello is now a lot better instrument than before. It still needs more work, though. The original soundcards that were replaced by the Studer-card are faulty in an unknown way and could be repaired. Tone pot is not in use, also the overall feel of the keys could be improved. This is maybe the most important bit in how well the mellotron works. A badly adjusted key can even cause the sound to be out of tune, since the tape won't play at the correct speed. I hope I can write more about the improvements with our mello in the future.