various repair topics
2011-02-22 by David Rogoff
Hi all.
I spent a lot of the long weekend buried in CS80 guts and thought I'd
share some of what I found.
First, on the topic of dying chips, I had to replace an IG00052 filer EG
chip yesterday. It wasn't totally dead, but the output wave shape was
very strange and inconsistent.
Next, for tuning, there's a really nice way that doesn't require holding
any keys and/or figuring out which card is active. I just grab the sine
wave output right off the M cards (pad CP1 -
http://dl.dropbox.com/u/9224623/trigger%20wiring.JPG). The way the KAS
works, if you just play one key, all 8 voices go to that note. So, just
hit A1/A4 as desired and all the voice cards have nice, clean sine waves
coming right off the VCO without holding any keys. I think the easiest
way to tune is to run these, one at a time, into one input of an
oscilloscope and run a reference sine wave (I use ClearTune on my
iPhone, which lets me easily change octaves) into the other input and
then set the 'scope to X-Y mode. It's a piece of cake to see the beat
frequency and get it perfect. A strobe tuner would work great also -
I've got Peterson iStrobeSoft on my iPhone too.
For calibrating the EG times, I soldered wire loops onto each M card on
the TRG input (removing the trigger wire temporarily) and the EG output
testpoints. I then connected a wire to the square wave output of the
Sub Osc and connected it to the trigger inputs of all 16 voice cards and
the trigger input of my 'scope:
http://dl.dropbox.com/u/9224623/trigger%20wiring.JPG
Now I can go through the calibration procedures (
http://therogoffs.com/cs80/CS80%20Adjustment%20Procedures%20and%20updates.PDF
). It's still very slow going. I got the first card all calibrated and
then displayed its output on the 'scope along with each of the other 15
cards one at a time to get them all to match. This is much easier and
faster then trying to calibrate them each individually and consistency
from voice to voice is the most important thing anyway.
Back to my digital day-job now!
David
I spent a lot of the long weekend buried in CS80 guts and thought I'd
share some of what I found.
First, on the topic of dying chips, I had to replace an IG00052 filer EG
chip yesterday. It wasn't totally dead, but the output wave shape was
very strange and inconsistent.
Next, for tuning, there's a really nice way that doesn't require holding
any keys and/or figuring out which card is active. I just grab the sine
wave output right off the M cards (pad CP1 -
http://dl.dropbox.com/u/9224623/trigger%20wiring.JPG). The way the KAS
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works, if you just play one key, all 8 voices go to that note. So, just
hit A1/A4 as desired and all the voice cards have nice, clean sine waves
coming right off the VCO without holding any keys. I think the easiest
way to tune is to run these, one at a time, into one input of an
oscilloscope and run a reference sine wave (I use ClearTune on my
iPhone, which lets me easily change octaves) into the other input and
then set the 'scope to X-Y mode. It's a piece of cake to see the beat
frequency and get it perfect. A strobe tuner would work great also -
I've got Peterson iStrobeSoft on my iPhone too.
For calibrating the EG times, I soldered wire loops onto each M card on
the TRG input (removing the trigger wire temporarily) and the EG output
testpoints. I then connected a wire to the square wave output of the
Sub Osc and connected it to the trigger inputs of all 16 voice cards and
the trigger input of my 'scope:
http://dl.dropbox.com/u/9224623/trigger%20wiring.JPG
Now I can go through the calibration procedures (
http://therogoffs.com/cs80/CS80%20Adjustment%20Procedures%20and%20updates.PDF
). It's still very slow going. I got the first card all calibrated and
then displayed its output on the 'scope along with each of the other 15
cards one at a time to get them all to match. This is much easier and
faster then trying to calibrate them each individually and consistency
from voice to voice is the most important thing anyway.
Back to my digital day-job now!
David
