****Sequential Circuits Pro One **** SURVIVAL * SURVIVAL * SURVIVAL ** Parts ** Parts ** Parts ** Parts
J-Wire & Membrane style keyboards
The more reliable & preferred 37-note keyboard for the Pro One is the J-wire style keyboard, and it is possible to visually identify a J-wire keyboard from the membrane switch style keyboard. All keys from a J-wire style keyboard have 2 small plastic numbs molded into the top-back of each key as seen in Image #1. Keys from a membrane switch style keyboards can be identified by the metal mounting clips protruding from the top back of each key as seen in Image #2.
Click image to view larger version
The keyboard ribbon cable assembly connects the 37-note keyboard to its
associated 16-pin socket on the PC Board from a 16-pin socket located
under the keyboard itself. The keyboard ribbon cable has a red line at
one edge designating the position of Pin #1. The keyboard cable MUST be installed into the keyboard's socket prior to mounting the keyboard to the bottom panel. Connect the
cable's pin #1 to the keyboard's socket pin #1, and the other end to the PCB socket's pin #1. (See Image #3)
Although any Pro One can use either a J-wire style or membrane style keyboard,
the probability for finding an original replacement J-wire keyboard is very unlikely
since they only exist in other Pro Ones.
In the past any successful repairs to the troublesome membrane switch contacts
were only temporary at best due to the inherent unreliability of the switch design.
At this time a MIDI to CV converter is the easiest solution to by pass a membrane
switch keyboard keyboard and trigger a Pro One. However, if you choose to
continue to use a membrane switch keyboard, the rubber keystops are the same
for all Pro One keyboard, whether J-wire or membrane switch style.
The Pro One operations manual states the CV IN requires a 5v GATE and
1 volt/octave CV (0-10v range).. if any of your other keyboards can supply these
CVs then you should be able to control your Pro One directly from another
keyboard without the need of a MIDI to CV converter.
The Pro One's fuse is installed into the back of the square Red fusecap, and the fusecap is then inserted into the square fuseholder. The fuse and Red fusecap remain slightly spring-loaded when properly inserted into the black square fuseholder.
The Red fusecap requires replacement if its retainer clip breaks, or if the Red fusecap is simply lost or missing. The square panel mounted fuseholder requires replacement if broken or damaged. Inspect the fuseholder to confirm it is securely mounted into the metalwork, & inspect for any damage to the 2 mounting clips found at each side.
A Red fusecap replacement is $15, the fuse holder is SOLD OUT.
A 1/4 amp Slo-Blo fuse is required for use with 110 VAC, and an 1/8 amp Slo-Blo fuse is required for use with 220VAC. Pro One fuses are available for $5 each.
A PC mounted power replacement is the #S-048 power switch, and a panel mount power switch replacement is #S-054. Although completely different in appearance, each power switch serves the same purpose and is the same price.
The early Pro One's had a power system that mounted the transformer, power switch, voltage select switch, and fuseholder onto the PC board as shown in Images #1 & #2. Subsequent problems occurred whereas the PC mounted transformer would separate from
Click image to view larger version
the PC board during shipping, prompting a reliability design change that mounted the power transformer, power switch, voltage select switch, and fuseholder securely onto the bottom panel metalwork as shown in Images #3 & #4.