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Replacement Area 
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Some of the parts of our (E)SQs aren't available anymore. This makes repair real fun since you have sometimes to tweak around things to "emulate" those unavailable parts.

I've not tested all of the below hints on the SQ80, some of them are even completely untested but should work pretty well, since I derived the circuitry from some other schematics or application note.

Sad but true... These days one really calls for spam when publishing an email address on a website. But what the heck.

If you expect an answer please send plain text emails. HTML-formatted mails will be dumped automatically.

No Sound on your SQ80? Here's the checklist!

  1. All PSU voltages present?
    If not, fix PSU.
  2. Does the unit work otherwise, i.e., display, buttons, keyboard, MIDI all ok?
    If not, fix that first.
  3. Are the auxiliary on-board voltages -5V/+7V present?
    If not, check Q6 (MJE182), Q7 (7905), CR10 (1N5236B)
  4. Does the DOC output sig+/sig- into U31?
    • If not, check feedback path: I31 (MC34085), POT1 (5k), CR8 (1N914)
      Maladjustment of POT1 will lead to a silencend (or distorted) DOC output; in worst case you'll only hear some ticking/crackling noises.
    • Feedback path ok? Then replace U27 (DOC)
  5. Are the muxed signals present at the outputs of U36?
    If not, replace U36 (4051)
  6. Are CVs generated? Check input and output of U30 for CV presence.
    • If present at input, but not output, replace U30 (TL081)
    • If not present at input, replace U29 (AD7524)
  7. Are the CVs routed through accordingly? Swap U34/U35 and U37/U38.
    • Sound reappeared, but resonance is way off: replace U35 (SSM2300)
    • Sound reappeared, but panning is way off: replace U38 (SSM2300)
    • (Make sure that not all 4 of them are dead, before taking next step...)
  8. Check CEM3360
    • Signal is present at output, replace U39 (TL084)
    • Signal is present at input
      • Does the volume slider deliver proper VOLV (0-12V measured at R117)?
        If not, replace volume slider.
      • Is VOLV still present at U44, pins 5 and 10?
        If yes, replace U44 (CEM3360).
        If not, chase the signal and search for haircracks, cold solder spots, faulty resistors (R117, R119)...
    • Signal is not present at input: Check input of U39
      If signal at input of U39, replace U39 (TL084)
  9. Still no sound?
    Check jacks.
Whenever you "lost" a signal, i.e., it is appearing at the output of the previous stage but not reaching the input of the next stage, trace the line for hair cracks, cold solder spots, and eventually dead resistors (then R is infinite), dead diodes (they should only conduct in one direction, neither non nor both...), dead capacitors.  

PSU-Failure: The LM2925 Voltage Regulator

Ensoniq decided to use a combined 5V regulator / reset generator. Back in 1988 this was no problem since the LM2925 was easy to get, but nowadays its almost impossible to get one of these beasts. Fortunately, there's no magic inside this one and it could be easily replaced - so here's the schematics:

LM2925 Replacement
LM2925 Replacement Circuitry


Replacing the internal disk drive

click here (same disk interface but different machine :)