TR909 the queen of drum machines. No much more to say about this one, you love it or hate it. I do certainly love it!
The circuit is build in a way which allows a lot of extension work, as it is an almost modular concept.
The memory expansion slot had to make place for the connector of the extension box. Of course, the unit can be re-modified to its original version in within a couple of hours, no irreversibly changes have been made.
Also, on this unit, I replaced the firmware eprom with one holding the latest (or last software version if you can say so for a unit of this age) firmware,
which is known to have a better clock sync-timing. Important for recording sessions…
Got another one, which I repaired, but it was in such a bad state once I got it, that I was too disgusted to take any photos of it. This is how it looks now.
Did I mention that it didn’t work when i got it? it surely does now!
A service manual for the TR909 is available on Matrixsynth but I bought mine before it was available on the net from Mark Glinsky’s manual manor who is always a good source for nicely copied service manuals and schematics.