[sdiy] Noisy Kawai K3!

[Bob Weigel]

K3 was my first synth and I have the service manual here if needed...but 
definitely check the front end filter capacitors.  At this age they 
could be failing.  If you have an esr meter that makes it easier.  It 
will show if the high frequency response of the filter is going dead 
basically and if it's out of spec it is a strong hint that it's time to 
replace the cap.   If these capacitors fail they allow ripple to hit the 
regulator to such an extent that the voltage can fall below the headroom 
requirement for the regulator and this will allow a hum to get through 
to the rest of your circuitry.
     If it's not that...could be a partially broken ground somewhere or 
a damaged chip or who knows.  Usually if a chip starts to fail towards 
shorting, it will drag the power supply voltage down on one rail but 
depending ont he design it will usually blow a fuse before you hear much 
hum.  But a lot of possibilities.  If you have a scope monitor the 
voltage on the +- pins of an op amp (4 and 8 on a 4558 which I think 
they use some of in that unit).  It should be flat down below 10mV 
depending on how good your scope probe is and all. -Bob

Jonathan Lutz wrote:

> I have a K3 that's been nearly unusable since I purchased it due to 
> some serious noise/hum.   Where would one start in troubleshooting 
> this thing?    I noticed the K3 (along with my SCI Sixtrak, also 
> noisy!) doesn't use a wallwart like some more modern synths.. could 
> the cause be power-supply related or........?
>
> JON
>