Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

previous by date index next by date
previous in topic topic list next in topic

Subject: Re: [PolySix] Re: Dead Keys are Stuck in Arp

From: <backshall1@bellsouth.net>
Date: 2018-04-20

With the speed at which my messages are appearing, Yahoo must be using a satellite relay somewhere outside the orbit of the moon. Either that or we are 670,616,629 miles apart.
For the panel board, there is a slight possibility that something is physically being shorted out when the machine screws are tightened. The M3 screws that hold this board are supposed to have a plastic washer on them. Are the washers all there? More likely, there is some sort of cracked solder joint or trace that gets disconnected when the board is flexed. This board can get warped and sag quite a lot, particularly around the 1-8 buttons. I’ve heard this is due to heat from the transformer over the years.
I have seen several keyboard contact boards with bad diodes and/or blackened traces. I assume it’s from several acidic carbonated beverages spilled on the keys over the years. You can’t just wipe off the keys when that happens. The real damage is underneath.
Don Backshall
 
Sent: Friday, April 20, 2018 3:38 AM
Subject: Re: [PolySix] Re: Dead Keys are Stuck in Arp
 
 

Hello

Dons analysis is excellent. After your description of pressing the panel buttons, I'd say the cause for the stuck note/dead keys problem is a corrupted/broken diode either on the panelboard or the keyboard. If you look at the service manual page 7 (new board) or page 5 (old board), you will see, that the bus P10-P17 is shared between the keyboard matrix and the panel board KLM371, but the panel switches are returned to a different bus than the keyboard. If a diode in this matrix is letting currents pass in the wrong direction unpredictable things may happen.

If you had a battery leaking, then a diode might suffer from it. I had it several times, that the glass body of diodes got leaking, because the metal of the wire corroded, so a gap between the wire and the glass appeared and humid air could reach the inner of the diode, which again causes the diodematerial to change its characteristics.

Unfortunately the service manual doe not contain a schematic of the keyboard, so we cant tell which port line this is.

Florian


On 20.04.18 03:33 , jhatzia@gmail.com [PolySix] wrote:

 

Thank you Don- you really nailed describing my situation. I'm working on it again now. And was trying to reply to your comment to get a new description on the hanging note but it started working again..?

After leaving the synth on for a while I couldn't even get Chord Mem or Hold buttons to react. After cycling the power they reacted again but had hanging notes.. I was then pressing all the key assign buttons and after some clicks it started behaving properly... Now all those dead notes are playing fine (except the last G, A & A# are still very dead).. Very odd. I wouldn't be surprised if it happens again. I'm still unsure where a fault like that would be found in the circuit.

Well- I still have to install about 3 new button cap holders and clean the volume pot, so I would be surprised if the issue arises again, if it does I'll make sure to update this thread.