Sequential Circuits Prophet 5 Rev 3.2

• Serial number: 2249


• Unit taken out of storage after a long period of time. Boots and tunes, but makes no sound of any
  kind, apart from A440 tuning signal. Power distribution strip on bottom of PCB 3 partially open
  circuit on -15V path. Replace missing connections with external hook-up wire.


• Unit now partially works but in a very unstable manner. Electronics separated from chassis work
  and wooden element sent to woodwork shop for refurbishment.


• Control panel boards removed from unit. Facia cleaned, tantalum capacitors replaced with
  aluminium types and all pots and switches cleaned. Previous attempts to repair track work tidied
  up.


• Whilst instrument in dissembled state work on problems related to the instability. PSU striped of
  all capacitors both electrolytic and tantalum bead types. Replaced with modern aluminium types.
  Replace 2 x 6800uF computer grade capacitors. All three linear regulation devices replaced and
  thermally re-mounted with modern day equivalents. Devices attached to PSU board using fly leads,
  to avoid future lead disconnection whilst moving. Trimmer resistors for +/-15V rails replaced to
  provide more stable setup.


• On mains input side, frayed mains lead replaced with 3m cable and integral BS1363A mains plug.
  Unsafe and cracked square fuse holder (348 series) replaced with modern day equivalent. DP
  241-8-36 mains transformer replaced due to excessive mechanical noise and hum. Wiring replaced
  and re-terminated as required.


• CPU PCB 3 also cleared of all tantalum capacitors and replaced with aluminium types. Replace
  burnt 10R 1/2W resistors in +15V HV level shifter circuit. Replace badly repaired multiplexer IC
  with 3 x CD4051BE. Replace depleted 2/3A tabbed battery.


• In order to stabilise voice board PCB 4 detect and replace certain corroded IC sockets and
  replace. Remove and assemble new 60 way ribbon between PCB 3 & 4, some connection of which
  were going partially open circuit. Replace tantalum capacitors with aluminium types.
  Remove jack earthing wire and replace. Also change audio out jack with highly intermittent
  connection. Clean all others and replace jack nuts and washers.


• Keyboard cleaned, re-bushed, greased, aligned and cleaned.


• Reassemble unit with working electronics and test. Recalibrate VCO and VCF tuning. Check and
  calibrate final VCA levels between voices. Remove ‘resonance mod’ on voice 1, replace with
  correct 200K resistor and correct fault masked by modification (partial track disconnection
  around filter).


• Add new ‘Sequential’ and ‘Prophet-5’ labels to refurbished woodwork. Reload factory patches and
  perform full 1 week soak test.

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