[sdiy] You all missed my arp omni chronicles..

[Kevin Lightner]

>Oh my..what a basket case.  Several 4069 chips were bad.  Connectors 
>had been stuck on wrong and even pins reversed in interconnects. 
>One caused a transistor to decay then burn out for the sustain 
>voltage ref.  That was our final treat last night. But
>
>1) I swapped in an op amp for the AD envelope buffer...figured I'd 
>upgrade the 1458 since I saw no reason not.  Put in the 4560.  Now 
>my attack was fine...but as soon as the attack reached the voltage 
>rail WONK!  Sound dies.  After scratching my head a bit I finally 
>got around to scoping both the output AND the capacitor charging on 
>the other side of the buffer amp.  The cap did exactly what it was 
>supposed to do...the amp output....did exactly what I was hearing! 
>A guy in AH suggested that there are some op amps which actually in 
>a buffer ap will invert the output when you hit rail!  I had already 
>tried a 4558 also and this was the case.  The 1458 is the only amp 
>that works in that particular type of applications of the three! 
>Nice...to know that! :)
>
>2) There is a remaining strange problem.  The synth bass if you 
>release before it's envelope runs the course, triggers the low C on 
>release in place of the note that should continue to decay.  The 
>String bass and cello both do it no matter what.  All the envelopes 
>and everything work fine and consistent now.  Quite strange.
>-Bob




Bob,

You like long stories.

I'll share one.

When I was a lowly service tech at the otherwise mighty Roland US, we 
had a resident Japanese import manager and engineer/tech in our dept. 
I say "engineer/tech" with respect also, because I feel that 
engineers do not always make the best techs and vice versa. This 
person also was on the SH1000 or 2000 design teams. He'd been around 
for a while and knew both sides of design and serviceability issues. 
He was the liason to Roland Japan who also explained what failed and 
why and how to build products that were easier for techs to work on.

Well, when one of us techs couldn't find a problem, we'd often find 
ourselves tugging at this more experienced fellow's heels. In 
retrospect though, we couldn't have been in a better place: all docs, 
all parts, full replacement boards, power desolderers... we had it 
all. Yet often we were stumped.
Obviously we were hacks, swapped ICs with the wind and basically 
guessed our way to success.

After a while, this Japanese fellow grew tired of interacting with 
the "kids" on their repairs.
He usually then offered only one bit of advice, three simple words 
uttered in broken English.
Now with approx 20 additional years under my belt since those days 
and a much better tech, I  have come to realize that his advice was 
the best and most accurate advice I've ever heard.

Now I will share this sage advice: LEARN TO FIX!!



-- 
Regards,
Kevin Lightner

http://www.synthfool.com