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

[james meagher]

> It's weird, I can't find all of the caps on the voice PC on the parts list. C105 is there, but the next one listed is C122. Am I misunderstanding their parts list somehow?
>
> Still, 0.0022 is clear enough. 0.0022uF is 2.2nF.
>
> HTH,
> Tom
>

Blarrrggghhh!!! So from not-so-bad to worse! But first I should say . . .

. . . thanks Tom - that does help. I also noticed that some caps
weren't listed on the parts list. Luckily most of them say right on
them what they are.

So last night I managed to roughly reassemble the Voice 8 Saw Level
trimmer I broke when removing and replaced it back into the board.
Surprise, surprise, while not entirely gone, the problem of the overly
width-modulated DCO1 signal was vastly reduced! Voice 8 sounded and
showed on the scope to be almost completely in line with the other
voices. So I'm about 99% sure the problem is this voice 8 Saw Wave
Level trimmer.

Now back to blarrrggghhh!!!

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










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