Discussion about the Korg PolySix synthesizer

I'm really hoping I can get some help / advice from you all.  Ok, 
i'll state the facts once again:

My polysix fell out of tune last week, a few days before I was about 
to play a show, and I decided to get in there and tune it.  I got it 
rock solid in tune, and this is obviously where I went wrong - I had 
it plugged in still -  and closed the cover down to put all the 
screws in and saw a small flash from the center back portion of the 
inside.  It seemed like it came from the center back board that's 
screwed in with the metal plate, the one that holds the fuses.  The 
first of the two fuses blew out.  I looked around for quite some time 
to see if I pinched any wires against the case or something obvious, 
but couldn't find anything.  I bought new fuses and replaced, but 
they blow out immediately when powered up.  

I'm pretty handy with a soldering iron and such, can plunder my way 
through schematics - but not sure where to start and thought I better 
ask some advice.  Thanks in advance for any help.  The most I can 
offer this board is my patch dumps, I have a number that aren't in 
your files area.

--- In PolySix@yahoogroups.com, "hoggy_bogger" <yanbu@c...> wrote:
> I'm really hoping I can get some help / advice from you all.  Ok, 
> i'll state the facts once again:
> 
> My polysix fell out of tune last week, a few days before I was 
about 
> to play a show, and I decided to get in there and tune it.  I got 
it 
> rock solid in tune, and this is obviously where I went wrong - I 
had 
> it plugged in still -  and closed the cover down to put all the 
> screws in and saw a small flash from the center back portion of 
the 
> inside.  It seemed like it came from the center back board that's 
> screwed in with the metal plate, the one that holds the fuses.  
The 
> first of the two fuses blew out.  I looked around for quite some 
time 
> to see if I pinched any wires against the case or something 
obvious, 
> but couldn't find anything.  I bought new fuses and replaced, but 
> they blow out immediately when powered up.  
> 
> I'm pretty handy with a soldering iron and such, can plunder my 
way 
> through schematics - but not sure where to start and thought I 
better 
> ask some advice.  Thanks in advance for any help.  The most I can 
> offer this board is my patch dumps, I have a number that aren't in 
> your files area.



I would start by unpluging the power to each of the PCB's (use 
schematic to identify what plug is used for each board's power), 
then plug one at a time back in starting with the one you thing is 
least likely to be the problem. Switch power off plug in pcb, power 
on again, repeat for each PCB. When the fuse blows you know it's the 
last pcb you pluged back in. at pcb. Unplug it and plug the rest in 
a check the fuse does not blow (this will confirm that it is just 
this pcb). If it blows again you may have 2 pcb faults.

Once you located the problem PCB, I would look for something 
shorting out the power input, perhaps a component has been squashed, 
bent etc?

Sean

I'd check the Powersupply board for shorts - I can't remember but I 
think there should be a few transistors at the area - check them out 
for shorts.



--- In PolySix@yahoogroups.com, "hoggy_bogger" <yanbu@c...> wrote:
> I'm really hoping I can get some help / advice from you all.  Ok, 
> i'll state the facts once again:
> 
> My polysix fell out of tune last week, a few days before I was 
about 
> to play a show, and I decided to get in there and tune it.  I got 
it 
> rock solid in tune, and this is obviously where I went wrong - I 
had 
> it plugged in still -  and closed the cover down to put all the 
> screws in and saw a small flash from the center back portion of the 
> inside.  It seemed like it came from the center back board that's 
> screwed in with the metal plate, the one that holds the fuses.  The 
> first of the two fuses blew out.  I looked around for quite some 
time 
> to see if I pinched any wires against the case or something 
obvious, 
> but couldn't find anything.  I bought new fuses and replaced, but 
> they blow out immediately when powered up.  
> 
> I'm pretty handy with a soldering iron and such, can plunder my way 
> through schematics - but not sure where to start and thought I 
better 

> ask some advice.  Thanks in advance for any help.  The most I can 
> offer this board is my patch dumps, I have a number that aren't in 
> your files area.

> I'd check the Powersupply board for shorts - I can't remember but I 
> think there should be a few transistors at the area - check them out 
> for shorts.

I disconnected all the power to the other boards, and just had power
to the KLM-376, powered on and it blew the fuses (both 250v 1a on the
board).   Obviously there is a short somewhere in that board?  The D1
diode lights up for a sec when it's powered on, then  dims out.  

Can't seem to find any shorts in there, any idears?  I have a few
photos here of the board, maybe there's something obvious to you guys
(other than the fuses not being in there, took em out)

http://www.10eastern.com/images/polysix/poly1.jpg
http://www.10eastern.com/images/polysix/poly2.jpg
http://www.10eastern.com/images/polysix/poly3.jpg
http://www.10eastern.com/images/polysix/poly4.jpg
http://www.10eastern.com/images/polysix/poly5.jpg

> --- In PolySix@yahoogroups.com, "hoggy_bogger" <yanbu@c...> wrote:
> > I'm really hoping I can get some help / advice from you all.  Ok, 
> > i'll state the facts once again:
> > 
> > My polysix fell out of tune last week, a few days before I was 
> about 
> > to play a show, and I decided to get in there and tune it.  I got 
> it 
> > rock solid in tune, and this is obviously where I went wrong - I 
> had 
> > it plugged in still -  and closed the cover down to put all the 
> > screws in and saw a small flash from the center back portion of the 
> > inside.  It seemed like it came from the center back board that's 
> > screwed in with the metal plate, the one that holds the fuses.  The 
> > first of the two fuses blew out.  I looked around for quite some 
> time 
> > to see if I pinched any wires against the case or something 
> obvious, 
> > but couldn't find anything.  I bought new fuses and replaced, but 
> > they blow out immediately when powered up.  
> > 
> > I'm pretty handy with a soldering iron and such, can plunder my way 
> > through schematics - but not sure where to start and thought I 
> better 
> > ask some advice.  Thanks in advance for any help.  The most I can 
> > offer this board is my patch dumps, I have a number that aren't in 
> > your files area.

How do you check for shorts ? Obviously you should check for shorts
between any of the transistor's legs that exists in the Powersupply
section, particulary the 4 ones that are attached to the bck of the
metal case, using a multimeter.




--- In PolySix@yahoogroups.com, "hoggy_bogger" <yanbu@c...> wrote:
> > I'd check the Powersupply board for shorts - I can't remember but 
I 
> > think there should be a few transistors at the area - check them 
out 
> > for shorts.
> 
> I disconnected all the power to the other boards, and just had power
> to the KLM-376, powered on and it blew the fuses (both 250v 1a on 
the
> board).   Obviously there is a short somewhere in that board?  The 
D1
> diode lights up for a sec when it's powered on, then  dims out.  
> 
> Can't seem to find any shorts in there, any idears?  I have a few
> photos here of the board, maybe there's something obvious to you 
guys
> (other than the fuses not being in there, took em out)
> 
> http://www.10eastern.com/images/polysix/poly1.jpg
> http://www.10eastern.com/images/polysix/poly2.jpg
> http://www.10eastern.com/images/polysix/poly3.jpg
> http://www.10eastern.com/images/polysix/poly4.jpg
> http://www.10eastern.com/images/polysix/poly5.jpg
> 
> 
> 
> 
> 
> 
> 
> > --- In PolySix@yahoogroups.com, "hoggy_bogger" <yanbu@c...> wrote:
> > > I'm really hoping I can get some help / advice from you all.  
Ok, 
> > > i'll state the facts once again:
> > > 
> > > My polysix fell out of tune last week, a few days before I was 
> > about 
> > > to play a show, and I decided to get in there and tune it.  I 
got 
> > it 
> > > rock solid in tune, and this is obviously where I went wrong - 
I 
> > had 
> > > it plugged in still -  and closed the cover down to put all the 
> > > screws in and saw a small flash from the center back portion of 
the 
> > > inside.  It seemed like it came from the center back board 
that's 
> > > screwed in with the metal plate, the one that holds the fuses.  
The 
> > > first of the two fuses blew out.  I looked around for quite 
some 
> > time 
> > > to see if I pinched any wires against the case or something 
> > obvious, 
> > > but couldn't find anything.  I bought new fuses and replaced, 
but 
> > > they blow out immediately when powered up.  
> > > 
> > > I'm pretty handy with a soldering iron and such, can plunder my 
way 
> > > through schematics - but not sure where to start and thought I 
> > better 
> > > ask some advice.  Thanks in advance for any help.  The most I 
can 
> > > offer this board is my patch dumps, I have a number that aren't 
in 
> > > your files area.

This could be a number of things.  Start with the cheapest first: test 
the rectifiers in-circuit with the power off using the diode checker 
function of a typical DVM.  Check the big electrolytic caps for dead 
shorts..in fact, just replace them.  With the fuses removed, turn on the 
power and measure the AC voltage that appears across the two lower clips 
of the fuse holders.  IIRC it should be around 30VAC.  Unbolt the board 
from the back fo the case and make sure there is no crud underneath 
causing shorts.  Q6 looks a little odd, is the lower lead actually exposed 
going up the side of the part?

  Just a few offhand guesses to get you started...

Crow
/**/

On Sat, 14 May 2005, hoggy_bogger wrote:

> > I'd check the Powersupply board for shorts - I can't remember but I 
> > think there should be a few transistors at the area - check them out 
> > for shorts.
> 
> I disconnected all the power to the other boards, and just had power
> to the KLM-376, powered on and it blew the fuses (both 250v 1a on the
> board).   Obviously there is a short somewhere in that board?  The D1
> diode lights up for a sec when it's powered on, then  dims out.  
> 
> Can't seem to find any shorts in there, any idears?  I have a few
> photos here of the board, maybe there's something obvious to you guys
> (other than the fuses not being in there, took em out)