After getting the power supply rebuilt, the transformer replaced and the mess of all the modification boards and wiring removed, the synth was playable, but far from a pleasure to play. The keyboard was in really bad shape with many keys not playing and others double triggering. That said, those wonderful warm tone from the Prophet 5 were emerging and just begging for this synth to be restored as best I could.
Unfortunately, the Pratt-Read keybeds on this era of synthesizers do not age well with regular use or unless meticulously cared for. They are made of a failure prone PCB attached to a metal chassis, with metal key frames pivoting on the chassis, using springs to provide tension return the keys. The key bushings also dry up and become unusable, the bus bar wires (j-wires) are easily be bent out of position and the buss bar can oxidize and prevent good contact to properly activate a key when played.
After removing the keybed, it was clear that this keybed needed a full overhaul. It was very rusted from exposure to the elements and for all I know, it seemed like a beer or other liquid may have been spilled inside it as it was rusted and the remaining paint was flaking off. It was clear I’d need to disassemble it entirely, strip it down and finish it.
First, I removed the springs and the keys from the keybed and then carefully removed the PCB from the keybed. Many of the key frames were very oxidized and were very difficult to remove. Once I had the keybed chassis free, I worked on leveling out the keystops which were all out of whack from years of use and abuse. Pliers, a 1-yard level and patience were key.
While I had the key caps removed, I removed the deep scratches with fine sandpaper, then polished each one individually using a series of car polishes and finished them off with a buff and wax.
Next, I stripped what was left of the paint off with paint stripper and sanded the chassis smooth. I then primed and gave it several coats of paint.
To reassemble the keybed, I needed to clean up the keyframes to get them to reseat on the chassis. Due to the amount of oxidation, I needed to sand and file out the grooves on the keyframes to get them to have enough play to freely travel up and down.
Once complete, I reinstalled the springs and the key caps on the frames. With the keybed reinstalled, I then began to work on straightening out the j-wires and ensure their travel and action were relatively consistent. A few had bad contact on the buss bar due to oxidation or dirt, so a little cleaning, a scrub or slight sideway adjustment got all of them working evenly. After many hours of work, I was rewarded with a very playable and even response across the keyboard with smooth polished keys.
Several of the potentiometers on the Prophet 5 had been sheared off by by some kind of accident. The shafts of the original pots are plastic and thus susceptible to breaking off by shear force. Since this Prophet 5 had apparently been sitting in a damp place and by the ocean, many of the metal components had become oxidized and needed attention.
Even the pots that were not broken were all corroded and had poor action. While they could all be cleaned and salvaged, I chose to replace them with a new set of pots. While not inexpensive, I figured this synth should have the best since I was taking it to a full restoration. Unfortunately the type of pot used on the Prophet 5 is a unique one. Though they are all 10K linear taper, the size of the pot, shaft length and direction of the ‘D-shaft’ and pin dimensions are unique and not an off the shelf part and need to be special ordered.
After the pots were replaced, and matched with matching knobs for the pots that were damaged, I replaced all of the knob caps with the awesome Prophet 5 Knob Cap Kit from Techsmechs. With the new pots installed with new knob caps this synth was now looking much better!