[sdiy] Ensoniq ESQ-1 Serving Questions

[Nate Reeves]

This reminds me on a problem I had with an ENSONIQ MIRAGE DSK

It loads the os and sounds/programs fine, but the keyboard controller  
IC is bunked as far as I know.

I thought of replacing it but as I got it for next to nothing I rather  
not try and repair that...

 From talking to the Mirage group on Yahoo...

Re: [Mirage-Net] Re: MIRAGE DSK 1 SERVICE NOTES?

On Wed, 2009-01-21 at 21:41 +0000, nmr2 at ... wrote:
 > it sends over nothing when i bang on the keys but when i play a
 > sequence on the one with the keyboard issue it DOES play the other
 > Mirage....so no notes out from the keys to the other one but from the
 > SEQ seems to work fine! maybe i should try to record a sequence with
 > the keys and see it it records? i dont the the keys are being scanned
 > so its either the diodes, the connector, or the MCU 8^(

No, it sounds like it's not doing much with the keys then.

The keyboard is scanned by U1, which is a mask-programmed 6502-variant.
They're used for the keypad in ESQ1s and the like, where they are
notorious for failing. Eep. Doesn't sound good, eh?

Pins 4 to 19 of U1 are pulsed in turn to strobe one side of the keyboard
matrix, and the returned keypresses come back through U2 and U5, which
are quad comparators. At this point I get fuzzy on the details, not
having played with a Mirage keyboard's insides for *quite some time*...

IIRC the keys are scanned in groups of four, with an "up" and a "down"
contact for each key. Velocity is determined by how long it takes for a
key to go from "up" through "neither" to "down". I think the uA339
comparators do something to clean up the signal.

Now, just a thought, but if one set of comparators isn't working, it
will either never see the "down" signal or never see the "up" signal.
Either way, it won't know what to do and won't emit any noise. You
should check with an oscilloscope to see if the inputs and outputs of U2
and U5 make sense. Here's what I'd do:

Use the 'scope to check for pulses on the outputs that go to the
keyboard (pins 4 to 19). Determine the cycle time to go through all
keys, and set the 'scope up so I can see two pulses from one of the
strobes. Set the 'scope up to trigger on one of these pulses.

Next, look at the inputs to the uA339 comparators. Find out which one
changes when you press a key. You'll see *something* happen, which will
change depending on which key you press. You should see an input
disappear from one chip and reappear at the other.

Now check to see if the comparator outputs follow suit. If not, change
the comparator. If that still doesn't work, then U1 may be faulty.

Of course, I could be utterly wrong about how the keyboard works. I
haven't had one apart for nearly ten years...
On Apr 18, 2009, at 9:16 PM, Kyle Stephens wrote:

>
> I've been meaning to get a probe, and I've an imminent reason now,  
> heh.
>
> Thanks :)
>
>
> _Kyle
>
> --- On Thu, 4/16/09, Scott Nordlund <gsn10 at hotmail.com> wrote:
>
>> From: Scott Nordlund <gsn10 at hotmail.com>
>> Subject: RE: [sdiy] Ensoniq ESQ-1 Serving Questions
>> To:
>> Cc: synth-diy at dropmix.xs4all.nl
>> Date: Thursday, April 16, 2009, 5:44 PM
>>
>>> That's a cluster of 8. From my experience with those
>> machines, I
>>> somewhat doubt that it's diode-related, but rather a
>> defective keyboard
>>> controller.
>>>
>>> The keyboard is organized in 8 rows of 8 columns. So
>> if you select a row
>>> (a cluster of 8 consecutive keys) with a diode tester,
>> you should see a
>>> connection to the 8 individual columns: for these you
>> have either the
>>> idle column or the pressed column.
>>
>> If you're lucky, it could be a broken connection
>> somewhere.  You should be able to figure it out with a
>> continuity tester and/or logic probe.
>>
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