EMS Synthi 100

Bespoke Operational Manual

EMS SYNTHI 100 MANUAL V3Download

Patch Recall Sheet

SYNTHI 100 PATCH SHEETDownload

From the workbench

Restoration videos

Restoring Pete’s EMS Synthi 100 on the bench at the University of West London. After a thorough clean, Part 1 diagnoses the faults, Part 2 restores the linear power supply and Part 3 continues the repair.

Its famous 256 digital sequencer needed a five-part repair of its own. Part 2 re-caps the circuit cards and devises a plan. In Part 3 every IC was socketed and tested, turning up almost 20 faulty chips, and custom extender boards were made so the cards can be probed while running, with plans to share the design so other 256 owners can make their own. In Part 4 the extenders are used to debug the recirculation circuits and shift registers; removing the Time Extender Board got it playing back recordings again. Part 5 is the finale.

The Synthi 100

EMS Synthi 100 Repair Part 1 – Diagnosis

Chapters 5

  1. Intro – the symptoms
  2. Following the mains input
  3. The two power supplies
  4. Big old capacitors
  5. Ripple on the -12V rail
EMS Synthi 100 Repair Part 2 – Restoring the Linear PSU

Chapters 10

  1. Intro – bench testing the PSU
  2. Ripple at 2.2kHz
  3. Inside the power supply
  4. The 10,000µF capacitor
  5. Replacement caps
  6. New bridge rectifier
  7. Repairing damaged traces
  8. Testing for ripple
  9. Result
  10. Securing the capacitor & refitting
EMS Synthi 100 Repair Part 3

The 256 sequencer

EMS 256 Sequencer Repair Part 1

Chapters 9

  1. Intro – stuck on start/stop
  2. The power supply & back panel
  3. Inside: Nixie tube & card rack
  4. The power supply board
  5. Removing the cards
  6. Testing & replacing the caps
  7. Checking the voltage rails
  8. First power-up – it runs!
  9. Speed control & what’s next
Part 2 – Re-Capping the Circuit Cards

Chapters 10

  1. Intro – no recording, no pitch
  2. Pulling the cards
  3. Triggering now works
  4. Testing the layers
  5. Memory test with the BeatStep
  6. Matching schematics to boards
  7. Plan: making extender cards
  8. Board-by-board fault finding
  9. Six faulty ICs on the A-to-D board
  10. The full chip list & plan
Part 3

Chapters 7

  1. Intro – every IC now socketed
  2. What’s working now
  3. Faulty chips board by board
  4. Designing an extender card in KiCad
  5. Pin-outs from the schematic
  6. Ordering with the PCBWay plugin
  7. Why make extender cards?
Part 4

Chapters 15

  1. Intro – the extender boards arrive
  2. First fit test
  3. Fitting board E on an extender
  4. Power-on & probing the clock board
  5. Checking board F timing signals
  6. Comparing working & faulty layers
  7. Layers one & three working
  8. Layer two: a 5V rail fault
  9. Oops – capacitor on the wrong rail
  10. Test rig setup
  11. Recirculation board signals
  12. Probing the memory boards
  13. Missing shift register input
  14. Removing the time extender – it records!
  15. Wrap-up
Part 5 – Finale

Chapters 8

  1. Recap of the series
  2. The faulty 7404
  3. Moment of truth
  4. Setting up three oscillators
  5. Recording via external clock
  6. Playback on internal clock
  7. Demo
  8. Thanks & wrap-up
Synthi 100 playlist on YouTube
EMS 256 Sequencer playlist on YouTube

More from the collection in the London College of Music playlist on the Really Nice Audio channel.