One of the best upgrades you can get for your Zendrum is the integrated wireless option. This adds an internal MIDIJet board along with a battery compartment for a single 9-volt that powers both the Zendrum board and the MIDIJet. I cannot say enough good things about this setup, it simply rocks. Once you've tried it you'll wonder how you ever got by being tethered with a MIDI cable!
Of course keeping the option to go back to being wired is important too, if for nothing else than to have a "plan B" should things go wrong. For instance you may have forgotten to bring or charge your batteries, or perhaps there is too much radio interference at the gig. Whatever the circumstances, it's important to be able to go back to using a wired connection at will.
Which brings us to the point of this article, because if you have one of the first crop of Z4 boards and utilize any Roland drum modules, you probably have discovered that a wired connection (i.e. not using the MIDIJet) simply no longer works! The Zendrum powers up fine, but no amount of banging on the triggers will register with the Roland unit. The official explanation for this that I've received from the Zendrum folks is that the Roland units expect just a slightly higher electrical current than the Z4 is providing at the MIDI port, even though the Z4 is adhering to the official MIDI specification.
One workaround for this that I stumbled on is to rectify the MIDI signal before it reaches the Roland unit, by doing a pass-through on another unit. In other words, by placing an additional MIDI device between the Zendrum and the Roland unit, the MIDI data signal is boosted to a level that Roland can pick up on. This would seem to contradict the notion that the Z4 board is operating correctly and that it's the Roland unit that is at fault, but i can't speak to that -- I only know that using a middle-man approach here works. Of course that adds a bit of complexity to your rig, and it's not always practical to drag around secondary MIDI devices, so it's less than an ideal solution.
I've received information from one of the Zendrum electrical engineers on how to affect a more permanent fix, as I will describe here. This fix involves opening up your Zendrum and taking a soldering iron to it. If you're not comfortable doing either of those things, then stop reading now. Even if you *are* comfortable doing this, I would encourage you to first contact Zendrum corp and discuss your options. I'm making no warranty against performing this fix, and I certainly won't take responsibility if you brick your axe. Nuff said.
The fix involves shorting out one resistor on the main Z4 board, either R10 or R13. Removing one of these from the circuit path with increase the amount of current that leaves the MIDI port, bringing it in line with what Roland modules expect. The simplest way to short out one of these resistors is to place a blob of solder on top of it. As long as you are very careful about not getting solder anywhere else on the board it should be a piece of cake.
Details of the fix plus photos of my axe under the knife...
One thing I learned about my Zendrum is that the leads to the battery case are very fragile. It turns out that every time you swing the battery compartment out, the wires that are soldered to it twist a tiny bit. One of mine was just barely hanging on and indeed snapped off during reassembly. Call me paranoid, but I would try to limit how often you open and close the battery compartment. Over time I'm sure the lead will snap off on its own. If you ever find that your axe no longers powers up from the battery, this would be the first thing to check.