midiverb II fettling

Alesis Midiverb II front panel

I bought a Midiverb II a while back, and when it arrived, it was dead.

It was advertised as working so I should’ve sent it back, but it was thirty quid and I thought I’m a super–DIY-electronics-pillock who totally knows what he’s doing – I’ll have this fixed before bedtime.

Four years later, and the Midiverb had fallen into a tiny gap between the guitar amp I got when I was fifteen and an Ikea shelving unit, still waiting for me to resurrect it.

Here it is in its dead state:

Midiverb dead state - all LEDs on, nothing on the numeric LED display

The dust! You’d think I’d have given it a bit of a wipe before taking a photo.

And inside – the board takes up about three-quarters of the rack.

Overview of the Midiverb II circuit board

The big square chip with the sticker on it is the magic Alesis reverb chip, and the chip to the left is the DAC.

The ICs above are for memory, and on the left-hand side there are some old-fashioned silver-topped TL084 quad op-amps, some of which might be used for output.

I’m guessing because there’s no schematic available, which makes it more exciting/fruitless, although the Midiverb III service manual might be similar in some ways. Anyway, for the Midiverb II this page on wolzow.com gives a far better impression of the insides than I ever could.

Here’s a random picture of the power regulation bit – the Alesis external PSU is a 9V AC adaptor, which gets rectified into +12V, -12V and +5V.

Closeup of Midiverb II power supply

I optimistically replaced the capacitors in this section a while back, plugged it in, and when it still didn’t work I thought, oh well, that’s me fresh out of ideas.

Looking at the date codes on the ICs this seems like it was probably a good thing to do anyway.

I rechecked the +5V power supply after reading this post on anlage-e – seems like some of the decoupling capacitors go bad after a while – no shorts, seemed fine.

Recently I plugged it in again and boringly got the same result, all LEDs on, no LED display. Maybe something to do with the microprocessor? I wondered if the reset line on the 80C31 wasn’t going high – measured it on the oscilloscope, it seemed to be blipping high when plugging the MVII in.

Alright, next thing – clock on the 80C31, it should be ticking along at 12MHz, what have we got?

FLAT LINE. (I should’ve taken a photo, although it wouldn’t have been very interesting). At this point I dragged the probe slightly, LEDs flickered, and the front panel 7-segment display burst into life.

Tears of joy.

I worked out that if I flicked the resonator next to the 80C31 hard enough with my finger it would jump-start the clock – restarting the Midiverb would produce the reset signal and get it going.

This wasn’t much of a fix, so I replaced the resonator with a brand new 12MHz crystal.

And it’s been working happily ever since. Here’s a picture of it under my Quadraverb, on the infinitely large patch 29.

Here’s an edit of the second thing I did with it, which might be an actual track eventually. Soz about the quality, it was onto cassette tape…

The main high-ish sound is the System 100 102 expander through patch 29 on the Midiverb, the bonky bass is the 100M clone, drums are a 606, and the pad-ish synth at the end is the Poly-61M. All running off the MC-4.

Anyway, what have I learned from this? The main thing is that digital things aren’t totally unfixable. Also, the lack of a service manual isn’t the end of the world.

Tagged under , , ,


  1. 30th June 2020Peter Dodge says:

    I have the same problem many I’ll try what you did

  2. 1st July 2020ua726 says:

    I’ve not seen this mentioned anywhere else, so I don’t know how prevalent it is. Worth checking the power supply as well.

    FWIW mine is still working happily six months later.

  3. 16th November 2020geeky says:

    I had the same problem a few months ago with a unit bought on ebay.
    The power supply was working fine, found a few shorted caps (and then replaced nearly all of them to be on the safe side).
    Noticed the leds seemed to be flickering and then checked the clock and found the resonator not working properly

  4. 17th November 2020ua726 says:

    Nice, glad you got it sorted out.

  5. 23rd February 2021Chris says:

    Any specific specs you have to look for when you replace that resonator, apart from frequency?

  6. 24th February 2021ua726 says:

    Honestly don’t know – I think I used this one, which in case that link goes dead in the future is a 12MHz crystal with a load capacitance of 30pF, product code CX016.

  7. 18th August 2021Jaap says:

    My Midiverb 2 shows the same symptoms (random leds) but it gets a clock from the resonator.
    The clock signal oscillates between 1.5V and 3V.

    If I read the SC80c31 datasheet correctly, the signal should be between 0.85V (0.2VCC-0.15) 3.6V (0.7VCC+0.1);

    Do you remember what the clock signal voltages were when you put in the crystal?

  8. 19th August 2021ua726 says:

    Just checked through my notes and my photos, and I can’t find anything. Bit surprising because I usually include gratuitous oscilloscope shots with blogposts whenever I can.

    I’ve had a look at some datasheets for the 80c31, and they all quote similar figures.

    Like you suggest, it sounds as if the resonator no longer has enough oomph to clock the processor. Given that the cost and effort involved is minimal, I’d be tempted to replace the resonator with a new crystal and then see where that gets you.

  9. 19th August 2021Jaap says:

    Thanks for checking, I really appreciate that!

    I replaced the resonator with a crystal, hoping that would help, but the scope readings were the same. Then I replaced U26 (74HC573 latch) and that did the trick: the MV is up and running now!

    I think I’ll replace the caps now to be on the safe side.

  10. 19th August 2021ua726 says:

    Nice! Glad it’s working now. One to bear in mind. Interested to know how you tracked that one down as well, were you seeing stuck inputs/outputs on the latch?

  11. 20th August 2021Jaap says:

    The outputs were stuck in a “random” state (different after each reboot). The inputs behaved like what I was expecting (changing state). I had a replacement 573 and thought putting that in wouldn’t hurt : )

  12. 20th August 2021ua726 says:

    Excellent, thanks for that Jaap.

Write a comment: