Restoring my SCI Prophet 5 rev3.3

The Sequential Circuits Prophet-5 is a pioneering analog synthesizer that revolutionized the music industry upon its release in 1978. Designed by Dave Smith, it quickly became a staple in both professional studios and live performances, revered for its rich, warm tones and versatile sound capabilities. With its innovative use of voltage-controlled oscillators (VCOs), filters, and envelope generators, the Prophet-5 allowed musicians to create a wide range of sounds, from lush pads to biting leads.

One of the Prophet-5’s most notable features is its ability to store and recall presets, a groundbreaking concept at the time. This allowed musicians to easily access and manipulate different sounds during performances or studio sessions, significantly expanding their creative possibilities.

Over the years, the Prophet-5 has remained highly sought after, not only for its iconic sound but also for its historical significance in the development of electronic music. Its influence can still be heard in countless recordings across various genres, making it a timeless classic in the world of synthesizers. This is how typical Prophet 5 restoration looks like.

Boards out. Shown above: mainboard (left), voice board (right). As you can see the wood was in a pretty bad shape. I’ve managed to fix that as well (more on that later).

Main panel out. Approaching bare bones.

Shower time. The only a proper way to remove all the dirt accumulated over the past 30 years.

Keys out. Time to install bushings where needed (luckily just one was in bad shape)

Cleaning keyboard contacts with alcohol.

Keys put in a hot bath. Some liquid soap was added.

Use a sponge and rub each key. Then wash away everything with hot water.

Putting back black keys first. That’s the way you want to do it, else, they won’t go in.

Time to replace CMOS chips on the control board. These tend to fail and you might end up in unit throwing random values each time you tweak a knob. While there, replace tantalum with electrolytic. There’s something like 25 caps or so, not much.

Old chips removed, sockets soldered in, new CMOS chips installed (use sockets, it will save you a lot of time in the future if some chip needs to be replaced). Potentiometers prepared for air compressor cleaning + contact spray “wash”.

PSU board. My advice, replace all capacitors, including the tantalum ones. These tend to fail after 30 years. The last thing you want is a failure on a PSU board. Also replace those three electrolytic capacitors. Apologize for the blurry photo. But you can notice those small “blue pills”. These are tantalum caps, to be replaced with electrolytic of the same value.

New 6800 uF caps are smaller, they won’t fit the metal holders. But don’t worry, as soon as you screw in those three regulators, the board will become fixed in.

Putting boards back in.

Another view this time with its little brother Pro-One which I also restored:

A quick demo of my Prophet 5 rev3.3 VCF FM in action, one of its trademark sounds, used countless amounts of time in film, soundtracks (John Carpenter et al):


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