[sdiy] Akai AX80 weird PWM behaviour on Voice 8 when Saw wave enabled

james meagher w.james.meagher at gmail.com
Fri Jul 13 18:16:20 CEST 2012

> Sounds like your battery needed changing, before your power supply blew. Well, you wanted a learning experience!
> Hopefully no big deal in the long run though, should be straightforward to fix.... (famous last words!)
> Adam

Yes, I wanted a learning experience. Last night's learning experience
was this - when your synth dies suddenly right when you're in the
middle of playing it, don't immediately storm off in a huff of
self-pity. Because when you return a few hours later with schematics
and meter in hand you may find out that you're not getting a reading
on anything in the power supply. Weird you think to yourself. Then
that lightbulb in your brain gets a dim glow as you reach over to
flick on your soldering iron . . . and sure enough the indicator light
doesn't come on. In the end you realize that you've been the victim of
a bad extension cord - nothing more than that. And now you feel like
an idiot.

I am including a new battery in my parts order, but as this original
battery still shows a solid charge of 3.2V, should I also be
suspicious that this weird memory behaviour could be caused by a bad
RAM chip or perhaps some of the other components (not much . . . a few
caps) that reside between the battery and the RAM?


> On 13/07/2012, at 6:31 AM, james meagher wrote:
>> I noticed when I got the board that the last ten patches on bank B
>> were silent. I didn't think too much of it at the time. Today I was
>> looking for a spot to save a patch and decided to check these blank
>> ones out further. I suspected that some levels had been set to zero or
>> no oscillators activated in either voice, or any of the other many
>> reasons a patch would be silent. What I found as I scrolled through
>> the parameters was that some said A1 or A2 instead of having a number
>> value, and still others had values that looked like numbers missing
>> some of their parts. I started making some notes of which parameters
>> in which patch locations had these anomalies to see if there was a
>> pattern between the patch locations. I also wanted to see if I fixed
>> the incorrect values and then turned on/off the board if they would
>> hold the newly inputted correct values or return to their previous odd
>> states. All was going well and the patches were holding with the
>> changes and making sound as they should. Then I got the final patch in
>> Bank B (patch 32) and was surprised that it made sound right off the
>> bat. This was especially surprising because as I cycled through the
>> settings in each parameters, some had the A1 and A2 values that the
>> other silent patches had had . . .
>> Then, right in the middle of a note the entire machine died. No sound
>> . . . no lights . . . dead. I'm feeling a tad Sisyphusian now and am
>> going to spend the rest of the evening playing with synths that work.
>> On the plus side, I was just thinking earlier this morning as I
>> flipped from the Voice Block Diagram to the Voice Board Schematic to
>> the Voice Board PCB image and made a nice little list of parts to
>> order to fix my Voice 8 and Voice 4 issues, "Wow, I've really learned
>> a lot in the past week".
>> James  :P
>> --
>> C'est La Guerre Moving Pictures Inc.
>> 364 Home Street
>> Winnipeg, Manitoba
>> R3G 1X4
>> (204) 918 9317
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C'est La Guerre Moving Pictures Inc.
364 Home Street
Winnipeg, Manitoba
R3G 1X4
(204) 918 9317

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