Vintage Synth Repair

I can help with this one ... I actually have two of these on the bench 
for restoration right now.

The F keys are unique in the Oz.  The 50240 top octave generator 
actually creates one full octave, plus 1 note.  In the case of the Oz, 
pin 15 outputs the upper F (F2), which is working on your system.  And 
pin 16 outputs F1, which is one octave lower, and is not working on 
your system.   (Only C1 through E1 use the 4013s to generate the lower 
octave signals.)

Check pin 16 for a square wave 1 octave below pin 15 (twice the period 
if using a scope).  If that is bad, the 50240 is bad, and will be 
difficult to find a replacement.   If pin 16 is OK, trace the signal 
through R31 and to the edge of the board at the F1 point on the pc 
board.  if all is well to that point, then the keyboard contacts are 
not working for the F1 key.

The contact wires on the bottom of the keyboard are very thin and 
fragile.  clean the contacts carefully with alcohol or naptha.  When 
looking at the bottom of the keyboard, the "tone" contacts (ie coming 
from the "F1" connection and others) should make contact slightly 
before the common bussed "trigger" contacts make contact.  Check for 
dirty contacts, broken contact wires, or misaligned contact wires.

 From the key contacts onward, all circuitry is used by all keys 
(summing and amp functions).  So the problem can't be out there.

The volume control problem could be bad grounding on the pot itself, or 
a broken ground wire between the pot and circuit board.  Or the control 
may have a solder bridge or other assembly related problem during 
original construction.

If you don't have the manual or R-E construction article (Feb. 1977), 
call Scott at Paia.  He can provide manuals for all the old stuff.

Hope that helps.  Good luck with it!

mj

On Apr 23, 2006, at 3:49 PM, vintagesynthrepair@yahoogroups.com wrote:

>
> Message: 3
>    Date: Sun, 23 Apr 2006 17:06:02 -0000
>    From: "easterleggs" <milotoll@...>
> Subject: PAIA OZ nuisances
>
> My Paia Oz has new 4013 chips, socketed, and a new amplifier chip.
> Before the repair, the lower half or so of the keyboard had fuzzy or
> intermittent notes.  All notes but one are fine now.  The low F does
> not produce any tone now.  Is it safe to assume this is a bad cap
> upstream of the oscillator chips...in other words, something
> associated with that particular key only?  I'd be curious to hear a
> layman's explanation of the tone-producing pathway from the
> perspective of a single key on the Oz...anybody wanna take a stab?
> Also, my volume pot has no effect.  The tone pot instead seems to
> control the volume to some degree.  Anyone experienced anything
> similar? Thanks for any help! --Stephen