Vintage Synth Repair

On Saturday 17 June 2006 01:55 am, Josh wrote:
> Hi Roy,
>
> Thanks for the info.  The synth must've heard me, cos the day after I
> posted here the problem disappeared.  It was apparently working
> flawlessly before it was shipped across Canada, so I guess it didn't
> like the journey!  I still hear the odd crackle now and then but it is
> much much better.
>
> I've made a note of your post for future reference.  I have to track
> down a service manual before I can check the FETs for substitutions,
> etc...  but it's nice to know where to start for a long-term solution
> if it becomes necessary.
>
> Thanks again!
> -Josh

Well,  hopefully some of that will be helpful when the time comes...

> > I don't recall the details of this model,  and my pile of their
>
> service data
>
> > isn't currently accessible to me,  but look at what they're driving the
> > outputs with.  I ran across the same problem in another instrument,
>
>  and it
>
> > turned out to be bad FETs at the outputs (the instrument I'm
>
> thinking of had
>
> > nothing but FETs in it,  nine of them altogether if I'm remembering
>
> right).
>
> > The part in question in that unit was supposed to be a 2SK30AY,  and
>
> in some
>
> > of the cases there had been substitutions made -- an ECG part with a
>
> 25V
>
> > rating had been put into a circuit that was running off a 35V
>
> supply,  so
>
> > they didn't last too long.  Another subsitute listed was another ECG
>
> part
>
> > that turned out to be a different package,  and was a bad cross,
>
> metal can
>
> > with 4 leads instead of TO92,  and a 50-volt part.  The Yamaha tech
>
> support
>
> > at that time told me that their original parts were selected for 90V
> > ratings...
> >
> > --
> > Member of the toughest, meanest, deadliest, most unrelenting -- and
> > ablest -- form of life in this section of space,  a critter that can
> > be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet
>
> Masters"
>
> > -
> > Information is more dangerous than cannon to a society ruled by
>
> lies. --James
>
> > M Dakin

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin