Emu Emulator II

Emu Emulator II

Emu Emulator II

This one had a bad power supply, and the customer had been trying to fit more modern replacements. Re-soldering cold solder joints bought the base power supply back to life on the bench, and when fitted to the Emulator the root issue was shown to be a shorted tantalum capacitor on the input to the -15v regulator. The harness was in a sorry state where it connected to the power supply, and a new connector was fitted. This unit has a lot of corrosion, especially in the sockets (and there are many of them!). It had memory issues that were a mixture of bad sockets, and bad driver chips. This is a complicated set-up with 2 Z80 CPU’s and a “Micro-controller”. The micro-controller here is not what we are used to these days as in MicroChip PIC’s, or Atmel AVR’s, but instead is a prom based “state-machine”.

 Z80-ICE Debugging an Emulator II

Z80-ICE Debug

Once the unit was booting OK it was time to deal with its other issues, crackly voices and wrong sound bytes played randomly. The random playing of bad sound bytes was, surprise, surprise, a rusty socket pin on a micro-controller ROM that was generating the wrong memory fetch addresses. This left crackly and dead voices. A TL084 was replaced to get one voice back, and a CMOS chip for another. General crackle was resolved by replacing the 3 CD4051’s that interface with the digital board. After this extensive work the heads were cleaned on the floppy drives, and switches/pots cleaned. Its alive and plays well, but the amount of time and parts to achieve this was high. As a note I made good use of a Z80 ICE debugging tool from Bob Grieb.

via This Old Synth – Vintage Analog Synthesizer Repair Portfolio Page.

9 thoughts on “Emu Emulator II

  1. The attention to this amazing piece of equipment if GREATLY appreciated Chris! I do incorporate some digital pieces into my setup, but only the stuff with analog filters can give me goose bumps! Looking forward to moving on to some different repairs! ; )

  2. Tom, Thanks for the kind comment, and you are not alone in the love of the old analog gear (which keeps me in business!)!

    I have Darren’s Emulator II here presently and have managed to find and fit an alternative supply that has the ability to set the strange set of power rails (+5v, +13.2v, +12v, -15v) that Emu chose for this machine. Of course, now power is on it we get to see all of its issues (which are 99% fixed now), and I will put it on the blog once it is done.

  3. Hi, Dan Wilson here, I’d be very interested to know which replacement PSU you sourced for your EII – although I’ve recapped mine I’m very aware that these units are notorious for spectacular failure and I’d really hate to kill this wonderful beast (mine was owned by the founder of OMI, as in Universe of Sounds CDs)


    Dan Wilson
    Hideaway Studio

    • Hi Dan,

      Here is a comment I gave on a user group thread. I purchased a few NOS Zenith power supplies and used one of those, but it is bigger than the original and there is work to do in order to squeeze it in:

      Note that I went with the Zenith ZPS 150a in Darren’s EII as it has adjustable
      outputs. The “+15v” rail is in fact +13.2V on the EII, and this was the only way
      I could achieve that.

      Why they did this I do not know, but I do know that it feeds some chips such as
      the SSM’s directly, AND on later units they connected 12V devices such as the
      disk drives to the 13.2V rail and left the +12V unused, so be careful.

      To fit a Zenith ZPS 150a you have to do some rework on the tray to lower the
      power supply as much as possible, and fit a whisper quiet fan to keep the heat
      away from the top panel. You also need to set it up with a dummy load, and of
      course adapt the cable-form.


  4. Can you let us all know what pin out / wiring combination you used on the ZPS-150 power supply alternative ? Some pictures would be good too 🙂 IE: Where does the -15v go at the ZPS end ? Cheers.

    • This really is a job for a tech as the installation needs to be safe, and the power supply needs to be brought up on a dummy load and the rails adjusted to the EII spec before connecting it to the EII. The ZPS-150 has floating outputs using a +Ve and -Ve pairing. If the outputs are not floating (i.e. tied to ground) then you cant do this but on the ZPS-150 you tie the -Ve pf the positive rails to zero volts ground, and for the negative rail you connect its +Ve to ground such that its -Ve will be in your example -15V.

  5. I have an Emu Emulator-IV that needs repair. Now on power up I get jibberish on the screen. I use it stand-alone with a keyboard so computer is not an issue. But I don’t know how to get it repaired. I’m in the NYC.CT. area of the country. Anyone know how I can get this lovely old critter repaired?

    Thanks in advance.


    • Wm,

      My sweet spot is vintage analog from the 70’s, or very early 80’s. Someone asked previously about the Emu EIV, but a service manual and parts could not be located so it could not be taken in. I do not know anyone that can service these, sorry.


  6. First I want to apologize for my ignorance, but please tell me, is there any way to put more memory on the Emulator II? I mean, like 8 or 16 Mb? People are changing the Disks for USB ports, i´ve been thinking in more memory, why not?
    Thanks in advance.

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