Back to MIDI basics with this one.
“I have a Sequence in my Korg 01/wfd and I want to synchronize it with a Roland MC-303 (Groovebox). I want the Groovebox to start when I start the Korg sequencer.”
While this is a specific question the answer works for most MIDI equipment with on-board sequencing, including drum machines. Simply run a MIDI cable from the MIDI out of the Korg to the MIDI in of the Groovebox. Set the Groovebox to receive external MIDI sync (MIDI clock). I don’t know the exact procedure for this on that machine, but it surely is in the manual. Virtually all MIDI sequencers can either use their internal clocks (the default mode) or be switched to external clock for synchronization with another sequencer (or synchronizing device). Your Korg should default to transmitting MIDI clock when you play a sequence, but you may want to verify this in the Master set up page. That’s it. Once the Groovebox is set to external MIDI clock you can press play and it will wait to receive timing from the Korg. Actually if it receives MIDI Song Position Pointer and start commands (which I’m almost sure it does, but you can verify this in its MIDI implementation chart) you don’t even have to press play on it. Just start the Korg and you’re rolling. This procedure is fundamentally the same when synchronizing any two MIDI devices.