Sequential Circuits Prophet 5 Rev 2 MIDI

Sequential Circuits Prophet 5 Rev 2 with Midi for sale at Soundgas following an extensive and detailed overhaul/upgrade for the current owner. 

This synth has been totally restored to the highest level by one of the best vintage synth techs in the business for the owner who intended to keep and play it for many years but unexpected expenses mean it's regrettably for sale. You will not find a better Rev 2.

No expense or time spared - took nearly 18 months from start to finish and is wonderful, reliable and a joy to play. It has Midi. The notoriously fickle keyboard has been upgraded with a new Fatar keybed which is a big improvement over the original (and won't require regular maintenance. A new power supply was fitted as well as many more new parts to create the ultimate reliable Rev 2.

Below is the full report from the tech which does not include details/cost of the meticulous panel re-screening (nor of the replacement keybed) - which turned out to be an extended and expensive process but worth the time/cost as it is virtually indistinguishable from the original factory finish.

Service Report/Notes - completed May 2026

• Full service requested. Subsequently, new keybed and new pots requested.
Concise Summary of Work Undertaken:
• Keybed replaced with new Fatar system and tested OK.
• All panel pots replaced (originals had already been previously replaced with dubious substitutes and
the pots glued onto the shafts); knob springs also replaced.
• Power supply, mains cable and plug replaced and tested OK.
• New memory kit installed, replacing original unreliable RAM chips and the firmware EPROMs. Unit
now runs v7.0C firmware which provides cassette support.
• Various missing fasteners and feet replaced.
• Z80 CPU replaced (died during calibration).
• New battery fitted, with current measurement resistor.
• 2 x bad SSM2020 dual VCAs replaced.
• Unit fully calibrated.
• Factory patches loaded.
• Unit provided no audio or boot initially.
• Pot knobs found to be glued to pot shafts, which are themselves not the original types. Knobs
removed with some difficulty and cleaned of glue deposits. New knob springs fitted. All 26 pots
replaced with remanufactured set matching the original design.
• Panel sent for reprinting.
• Replaced two badly damaged pins in 20-pin DC connector on Board 3 (+/-15V pins).
• Rebuilt 3-pin DC power connector harness powering Board 4.
• Replaced battery with new 3.6V type. PCB pad for +ve contact is unuseable; made wire tail for +ve
contact and attached this directly to steering diode pin.
• Replaced IC sockets for EPROMs, CPU and scratch RAM.
• Achieved unit boot; panel switches working but no pot activity. Traced problem to failed comparator
U339 (LM311); replaced U339 and recovered pot operation OK.
• Removed original power supply and fitted new purpose-built type, including toroidal mains
transformer. Tested new supply OK.
• Removed original keybed and fitted new 5-octave Fatar type with purpose-built mounting frame.
Fitted new wheel panel (the Fatar keybed is fractionally wider than the original) and made minor
metalwork modifications to remount wheels.
• Unit stopped booting. Traced problem to two failed patch RAM ICs (HM3-6508). These are long
obsolete and known to develop problems. Removed all eight patch RAM ICs and all EPROMs, and
installed new memory upgrade kit which provides single IC for patch memory and single IC for
firmware. Still no boot. Noticed IC309 (RAM write-protect logic) is the wrong family (74HCT); should
be 74HC. Replaced IC309 with correct type. Recovered boot and operation OK.
• Reseated all socketed ICs.
• Rough-tested all 10 VCOs OK.
• Calibrated instrument to factory spec. Replaced 2 bad SSM2020 dual VCAs (U422 and U413) which
were preventing Poly-Mod adjustment.
• Z80 CPU died during calibration process. Replaced with Sharp LH0080A (Z80 equivalent).
• Loaded original factory patches.
• Replaced various missing PCB and case fasteners, and 2 missing feet.
• Performed electrical safety PAT test.
• Tested all functions OK.
18th May 2026

Parts:

New Fatar keybed purchased/supplied by client
New panel pots (26) £300.00
New power supply £195.00
New RAM/ROM memory kit £79.00
Customs charge for new pots £34.38
Customs charge for power supply £35.40
Customs charge for new keybed £74.96
New knob springs (26) £13.00
Replacement PCB fasteners £4.00
Replacement case fasteners and feet £12.00
New mains cable and plug £11.99
Replacement CPU £12.00
New battery £11.90
New IC sockets £12.71