Earlier this year I acquired five Moog Slim Phatty synthesizers for The Phatt Bastard project.  Because the Slim Phatty is a discontinued product all these synths were purchased used.  In order to level the playing field I made sure that all the Slims had their firmware updated to the most up-to-date version, 3.21.690

This process went smoothly enough but I still noticed one thing.  The bootloader on one of the Slim Phattys was version 1.0 while the bootloader on the remaining four was version 1.1.  Updating the firmware didn’t seem to update the bootloader as well.

I tried the Moog forum but didn’t get a reply from the vendor.  After a while, though, a wonderful forum member posted the solution (ThunderBulldog – Thanks dude!).  I went through the update process and thought I’d share the experience here.

The update is not for the feint of heart plus it requires some specialized hardware.  The hardware is the Silicon Laboratories USB Debug Adapter.  It is available from Digi-Key, part # 336-1182-ND.


As indicated in ThunderBulldog’s post there are some software files from Moog required for the update.  This link connects to the dropbox with files.  I am not the host of these files and cannot say how long the link will be valid so if you’re thinking of updating get them and keep them stored away.  The link also includes the very well done update documentation.

The last item required is the USB Debug Adapter Flash Programming Utility.  This can be downloaded from the Silicon Laboratories site.

It should be noted that there is no Mac version of this software.  Only a Windows version.  I ran the Flash Programming Utility under Windows 7 running on a Parallels 13 virtual machine on a MacBook with High Sierra.

I should also note that before opening the Slim Phatty I wanted to test the interface to make sure everything worked.  I ran the Flash Programming Utility with the Debug Adapter connected to the USB port.  When I press the Connect button on-screen the device would light up but the software would display a “Not Connected” dialog.

After several tries where the same thing occurred I decided to try opening the Phatty and connecting the other end of the adapter (the ribbon cable) to the USB circuit board anyway.  My thinking was that perhaps a connection at the other end was necessary to complete the circuit required to establish connection. Presto!  Instant connection.

But I jumped ahead a bit.  Let’s talk about the disassembly of the Slim Phatty.  For the most part it was very simple.

Only three of the front knobs have to be removed;  Fine Tune, Value and Volume.  These are friction knobs and can be slid straight up and off.  Don’t wiggle the knob too aggressively or you might damage the shaft.  If you’re thinking of using a screwdriver to wedge it off you might think of using something to keep the screwdriver from scratching the crap out of your Phatty.  I suggest avoiding the screwdriver and to just pry it off instead.

After the knobs are off the rack ears can be removed and then all the screws on the left and right panels, the front and the back.  These screws are all the same type and size.  The plastic nuts holding in the eight I/O jacks must be removed as well.  Keep all your parts together in a little dish, lid, box, etc… I makes re-assembly way easier!



When sliding off the case be careful not to damage the I/O jacks or lose the 8 small plastic washers around each of the jacks.  Keep them together with your other parts.

Gently remove the case taking care not to damage the I/O Jacks

Once open the Debug Adapter can be connected to the USB circuit and the installation can proceed as per the documentation.  I won’t go into the detailed process here as it is thoroughly covered in the supplied document.  In a nutshell the process is basically;

  • Update firmware on USB circuit
  • Update firmware on Main board
  • Done



One important note during the second step of the update on the Main board.  The tab on the plastic connector will block it from being installed on the Main board.  The board can bend down slightly (toward the front panel) so you can put the connector on the pins just enough for them to make good contact.  DO NOT bend the board excessively or you’ll break it!

I’m thinking about sanding the tab off the connector on the Debug Adapter’s ribbon cable in case I have do to this process again as bending the board is a bit un-nerving. I’m planning on expanding Phatt Bastard in the future so this might be a good idea.

Both updates went perfectly and the whole process, including stopping to take pictures and make notes, took only a few minutes.  The documentation was quite complete and detailed.  The only thing I did which was unclear in the documentation was during the second step.

During the first step instructions indicates to check the box  “Erase all Code Space before download” before clicking the Download button.  The second step of the process does not mention this checkbox either way.  I opted to leave the box checked since I wanted to update everything anyway.  It worked fine.

I slid everything back together then tested the Slim Phatty before putting the screws back in.  It booted up fine and asked for a firmware upgrade as the documentation indicated it should.  I turned the unit off, screwed it back together and then proceeded.

Instead of the version of Slim Phatty firmware that was included with the update files, version 3.1.672, I updated to the latest Phatty firmware, version 3.21.690.

I put the Slim Phatty back into its place in the Phatt Bastard rack.  I should note that this was position six in a six voice polyphonic setup.  It used to be in position three but I noticed a recurring problem.  Sometimes the voice would simply cut out.  It would stop responding to MIDI commands from the controller (a Little Phatty).  Sometimes the Slim Phattys connected further down the chain would also start acting up.

This is when I began to suspect something was up with the earlier version bootloader on this one single machine.  I moved it to position six and started my search for an update solution for the bootloader.  Even in position six it would cut out or otherwise act up.  Since the firmware update to the bootloader it doesn’t seem to have these issues.

So that’s it…  Not too difficult and so far definitely worth the effort!