DSI Prophet 08 Repair

I recently suffered a rare attack of GAS1 when I found a very cheap DSI Prophet 08 Desktop on eBay. I've always wanted to own one of Dave Smith's Instruments and this was too good to pass up. Of course the reason it was so cheap is that it suffered from the well known encoder issue that affected early models in the run. DSI's fix was to replace the entire top board of the affected synths with one fitted with potentionmeters instead of encoders, and with a quick OS update everything is back to normal. Fortunately for me, and despite the issue occurring back in 2009, DSI still stock the replacement parts and I jumped at the chance to grab my screwdriver and have a nose inside a top-drawer piece of music hardware, and also document a few pitfalls along the way.

The patient

The first problem I encountered was getting into the thing. The instructions that come with the parts describes in great detail how to slide the top panel off without damaging the ribbons underneath (normally the trickiest part of getting into a synth) but failed to mention that the top panel is impossible to remove unless the end cheeks or rack ears are removed first. The screws that hold them in are huge and encroach on the controller circuit board that backs the top panel. The fact that this is the only design "fail" in an otherwise very well designed machine makes it even more annoying. It's only 6 screws though so it could be worse! Speaking of screws, there are only two types used inside, and all their holes are tapped, making life so much easier. Roland, I'm looking meaningfully at you here.

Inside, this is a beautiful synth. The 8 voices are beatifully laid out in front in pairs, and each pair has an RJ-45 socket for testing! If I had a decent oscilloscope to hand I would love to see what information can be gleaned from them. So much better than probing anonymous solder pads when trying to fix something. But on with the repair.

Inside the Prophet

As my Prophet is an early one, I need to make a small modification to the main board: removing one surface-mount component and shorting another. I think of myself as pretty handy with a soldering iron so ignored the warnings about needing a fine tip and tweezers and charged straight in.

They weren't kidding. To make matters worse, the two affected components are very close to one of the chips on the main board, meaning that they cannot be heated for long. In my rush I nearly tore the pads off the board with the component and I would have had a serious job trying to short it out as per the instructions. Fortunately my cack-handedness was a bonus later on when I was able to make the short simply by bridging solder over the gap, rather than with the suggested component lead. A quick check with a meter confirmed all was well.

Once it was back together it's like a new synth. Yes, it's not the one it was designed to be, which took care of the inherent problem of patch recall in instruments with analog controls, but it still responds nicely and pairs particularly nicely with Native Instruments RC48. I'm not used to its sound palette yet though, that will take a lot longer!

  1. Gear Acquisition Syndrome