Hmmm. Interesting one indeed.
Your analysis seems sound. If the top octave D's are OK, then your 50240
is OK.
Double check for solder bridges on the group of traces running underneath
the row of summing resistors along the edge of the board. Double check
for solder bridges around R33 and R34, and their traces to the 4013's.
If the replacement 4013 is toggling at all, it is probably OK. But, you
have to wonder why it blew in the first place. If there are input or
output shorts around that IC, that could have been why it blew. Did you
socket the location during replacement? If so, it wouldn't hurt to plug
another 4013 in there, but I don't think it's a defective 4013.
If you have a 'scope available, the outputs of the 4013's should be
exactly twice the period of the inputs, of course. Alternatively, these
could be probed with a high impedance audio probe to check for perfect
octaves at the inputs/outputs. (Watch your levels doing this ... these
are logic level signals and would be VERY hot going straight into an amp
... run through a dropping resistor or voltage divider setup before the
test amp.)
Also lift the keyboard assembly (carefully!) and check the J-wires for
the low D and D#. They could be bent and contacting each other. But,
then I would expect one of the low D's to actually sound 2 notes
simultaneously. So I don't really suspect that. But, worth a check.
Also trace the low D's keyboard connections to the edge of the PC board
looking for swapped leads or solder bridges at either end.
I'll open one of mine up and physically look at the pcb and wiring.
Perhaps something will occur to me upon looking at the actual hardware
instead of just the schems. ;-)
Good luck! Keep us posted!
mj
> Date: Thu, 13 Jan 2005 21:04:24 -0000
> From: "fishjaco" <fishjaco@...>
>Subject: Paia OZ d sharp = d note problem
>
>
>Hi all, I bought a Paia OZ to fix up and have run across a big
>problem. The low d sharp is giving the same tone as the d key. When I
>bought it the d sharp was only producing static when triggered. I
>traced the problem to a faulty cd 4013 (ic 3)chip and replaced it.
>Now it sounds a clear tone but the note is a d instead of a d sharp.
>The top octave works perfectly d and d sharp are seperate. I can't
>figure out where the note value is generated and what I should adjust
>or replace to fix it. I am still a novice to circuit design and could
>really use some help on this one. As far as I can tell somthing is
>mistranslating the divided voltage. Do all the 4013's need to be
>matched? Is my new 4013 bad? The logical problem would be that the
>wires leading from the top octave d in ic5 is hitting the low
>octave's d sharp 4013 section, right? But there are no wires crossed
>and no shorted circuitry that I can see. Also the d and d sharp don't
>even share a 4013 IC (the d is on ic2).
>
>The schematics are here:
>
>http://paia.com/oz.zip
>
>I asked them first for help but they would not reply.
>
>Thanks to anyone willing to help. I hope I can soon return such a
>favor the the synth community.
>
>Cheers
>
>Jake Fish