Yamaha CS80

Hi all.

I've been working on a CS80 for a bit now and finally have it all 
functioning to some degree.  I'm going through the full 
tuning/calibration procedure now
(http://therogoffs.com/cs80/CS80%20Adjustment%20Procedures%20and%20updates.PDF) 

and am having difficulty with the envelope times.  I've never tried this 
before.  On all units I've worked on, I've only needed to do the power 
supply and the usual M-card tuning.

However, this beast had some of its M-cards replaced from a very giving 
CS-60 and the EG times, filter cutoffs, and levels are really whacked 
out from board to board.  So, I'm trying to do the VCF Attack time on 
page 9 and VCA Attack time on page 15.  I came up with a nice trigger 
source: they specify a 3Hz square wave of +/-10v.  I found that tapping 
the output of the Sub-Oscillator square wave before its output resistor 
divider makes a great trigger. I just ran this, through a 1K resistor, 
to one input of my 'scope and then to the TR input of the M-card.  I 
trigger on this channel and then connect the specified EG testpoint to 
the other input of the 'scope.

This sort-of works, at least for the calibration of the short (4ms) 
time.  Triggering and observing signals this slow on an old, analog 
oscilloscope is a real pain.  Again, I got it somewhat stable for the 
4ms measurement. However, for the 125ms measurement, I don't have a 
prayer. With the low repeat rate and long time measurement, the display 
is too erratic to get any useful measurements. At work I have access to 
nice digital HP/Agilent 'scopes that can do this in their sleep, but I 
don't really want to bring the CS80 to work!  What did Yamaha intend to 
be used for this measurement back in 1976?  I guess an old analog 
storage 'scope would have worked, but those were pretty rare.

Anyway, I'd appreciate any tips from folks who have (successfully) tried 
this!

By the way, since I've had to pull the M-cards out to do the full 
calibration, for tuning I've been able to grab the sine wave right off 
the wave shape converter chip at pad CP1.   I run this into one input of 
my 'scope and my iPhone, running Cleartune (in pitch-pipe mode with sine 
wave) into the other 'scope input and set it to X-Y mode.  Beautiful 
Lissajous patterns that make it a snap to tune!  Of course, since the 
cards are out, the temperature isn't quite right and I'll have to do a 
final tweak when it's all put back together. For that I'll use the 
excellent iStrobesoft strobe tuner app from Peterson. It's $10, but well 
worth it, especially since a hardware strobe tuner from Peterson start 
at $100 and go up to $800!

Thanks again,

  David