Discussion about the Korg PolySix synthesizer

I suspect you are not applying the 47K resistor correctly.

Here is what that procedure is actually doing:

The CPU should be held in reset as power is first turning on or as it's turning off.
The 5V supply comes up as a ramp when you turn on power and a negative ramp
when you turn it off.   The voltage ramps from 0V to 5V, then stays there at power up.
What they want is for reset to be asserted (all of the LEDs on) until the voltage
is pretty close to 5V.   When you connect the resistor to the correct points, it 
changes the power supply setting a little bit so that the 5V output is lower than 5V.
(This is just temporary, while the resistor is connected)   Now you set the trim pot
so that reset just comes on at this new, slightly lower voltage.   Now if you remove
the resistor, the 5V should go back up to its correct value, and the LEDs should go off.

If nothing happens when you remove the resistor, that sounds to me like you are not
connecting the resistor correctly, so the 5V is not changing when you connect it, 
or when you remove it.  In that case, if you make reset come on, it will stay on.
Please measure the 5V supply at the 367 bd and confirm that it is dropping when you 
connect the resistor.

BTW, since you are using a lower value than suggested, you will get more voltage change
than what they wanted.  If you don't have a 56K resistor, use 47 + 10K to get 57K.  Much 
closer.   Just twist the leads together and then solder them to get a good connection.
The resistors should be in series, of course.

I don't understand any of what you said about resistors in parallel with zeners to make them 
work.  That really makes no sense.   You do need the correct current through the zener itself.
Too little and you won't get the proper voltage.  Too much and you will exceed the power 
dissipation of the zener and it will be destroyed.   So you need the correct series resistor.  
Here that is R41, 120 ohms.

Bob


--------------------------------------------
On Sat, 2/13/16, jw_dewdney@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:

 Subject: [PolySix] Re: PROGRESS!!!!
 To: PolySix@yahoogroups.com
 Date: Saturday, February 13, 2016, 2:44 AM
 
 
  
 
 
 
   
 
 
     
       
       
       Thus far the MG, EG, VCO, VCA, EFFECTS, PROGRAM
 sections have been unresponsive. Though the ARP, KEY ASSIGN
 and other basic functions seemed to work okay (and all
 voices seem to be more or less tuned (which is nice) even if
 I can only get the upper octave to work (one thing at a time
 right?) - SO - THAT BEING SAID - i thought i'd see if
 the reset and calibration procedure would set things right -
 so turning VR1 clockwise - i got everything to light up
 correctly - but when i remove the 56K resistor (was actually
 a 47K- hoping it was close enough) - there is no change in
 state (sad face)... so that's the current status.
 
     
      
 
     
     
 
 
 
 #yiv8125947532 #yiv8125947532 --

Hello,

    Please forgive me for saying this, but measuring the "resistance" of a
zener diode does not make a lot of sense.   This component was designed to 
break down in a controlled way when reverse-biased, at a predictable voltage level.
What you should be measuring is the voltage drop across the zener when it is in 
the circuit and powered up.   That's really the only thing you care about.   It should
be close to its rated 3.9VDC.   The exact voltage could be 3.7-4.1, depending on 
the current.  Zeners are not used when the voltage needs to be precisely set.   In 
that case some sort of laser-trimmed voltage reference would be used instead.
But you can tell if the diode is good (and if you have installed a 3.9V zener and not
a 1N4148.   A normal switching diode (1N4148) will not break down with only 5V reverse-bias,
so you would see the full 5V of the power supply across it   (the current will be essentially 
zero, so the 120 ohm resistor will not have any voltage across it)

   BTW, some time ago I uploaded some 'scope waveforms to the files section which you 
could look at and compare to what you see on your board.   Mostly they are related to 
the CPU and the DAC scanning the pots, as that function is often affected by pcb corrosion.
But you may find them helpful.

    Bob
--------------------------------------------
On Sat, 2/13/16, jw_dewdney@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:

 Subject: [PolySix] PROGRESS!!!!
 To: PolySix@yahoogroups.com
 Date: Saturday, February 13, 2016, 12:55 AM
       
       
       WOW. I can hardly believe it - everyone (who I am
 incidentally VERY thankful to for their patience) will be
 greatly relieved to know that I think i've LICKED my
 problem.
 
 How? On a weird
 HUNCH - and thanks to Roman and Bob's suggestion - I
 noticed that my D2 (the zener diode in question) was
 measuring with a MUCH higher passive resistance than the
 stock D2 zener on my original board (around 12 Megohm -
 compared to close to 10K on the original for the same
 polarity) - so after reading about shunting etc and how
 zeners typically need a high value resistor (like the 10K
 next to it) to help them function better in such circuits -
 that something was off. I was wondering how the HECK the
 zener i was using would work - assuming (perhaps wrongly)
 that the current would rather flow through the resistor. 
 
 Okay- sorry - i'm  being
 too verbose. But anyway- I swapped in the OLD D2 from my old
 polysix board - and NOW it sort of works - it's not
 perfect... I still have program patch 4 and 5 eternally
 lit... but other buttons and functions now seem to work. I
 haven't tried to see if I have audio yet.... but this is
 a HUGE leap forward to me... so again - thanks SO MUCH you
 guys for helping... !
 
     
      
 
     
     
 
 
 
 #yiv3657507060 #yiv3657507060 --

To troubleshoot the "staying in reset" issue when you try to do the procedure in the manual,
put your meter on the 5V supply at the KLM367 board and watch it when the 56 ohm resistor 
is connected and disconnected.  It should be dropping by a noticeable amount when the resistor
is connected, and then changing back when the resistor is removed.  

BTW, the first step, I think, is setting the supply voltages after giving things a chance to warm up.
Did you do that one?

Bob

--------------------------------------------
On Sat, 2/13/16, jw_dewdney@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:

 Subject: Re: [PolySix] Re: PROGRESS!!!!
 To: PolySix@yahoogroups.com
 Date: Saturday, February 13, 2016, 1:41 PM
 
 
  
 
 
 
   
 
 
     
       
       
       okay Bob... thanks for the calibration info.
 It's much more informative than the service manual, i
 did it by soldering the resistor across the connector pins
 inside the connector while the polysix was OFF. And then
 unsoldering it while ON....  So it makes more sense to me
 why it wouldnt work (unless a deeper problem is still at
 play here as Roman suggested). Perhaps i shouldnt be trying
 the calibration routine yet even?
 
     
      
 
     
     
 
 
 
 #yiv7491229255 #yiv7491229255 --