Re: [AH] Korg Polysix MG Rate Knob Issue

From Kenny Balys
Sent Sat, Apr 21st 2018, 01:43

I have worked on 2 Polysix's with battery acid damage.

My own was a total nightmare. Several times, I thought I had it, and
then it would start going off again after a few weeks. Its good now but
it took so many hours of bench time.

Next came my friend's Polysix. About the same as mine and I instantly
realized that I didn't have it in me to trace every single trace and pad
all over again. He decided to put the Kiwitechnics replacement board and
power supply into his. It was a miracle in both time saving and in
feature enhancement. So much time was saved too!

I will never ever repair an acid Polysix CPU board again. I will only
replace it with the Kiwi board.

The Polysix acid repair has got to be one of the very worst jobs. I
really feel for anyone doing it.

On 21.04.18 01:13 , Murray wrote:
> What happens with these boards is they are made out of fibreglass and
>  the acid gets into the weave. This will then slowly track all over
> the board and corrode the copper out of every throughhole via that it
> finds and will come back to the surface anywhere there is a hole in
> the board and there are lots. It is also impossible to remove as
> washing in IPA will not get into the weave and remove it completely.
> The only sure way to repair a board in this state is to replace the
> board.
>
> Don't use stripped wire. A better method is to get some fine choke
> winding enamelled copper wire for bridging the broken tracks. This
> can be found at any hobby store and is easy to work with, does a neat
> job and will not short to the board or other wires. You heat the cut
> end with a soldering iron and this will burn off the enamel just at
> the end for easy soldering.
>
> MH
>
>
> On 21/04/2018 11:31 AM, RJ Krohn wrote:
>>
>> the 367 board is one of the most frustrating problems i've ever
>> encountered. i solved all of the issues of a battery leak on that
>> board once. it was fine for a year. then, i started having problem
>>  manifest. turns out, the battery acid basically sat around, and
>> slowly ate thru traces over time.
>>
>>
>> my 2 cents would be this: look at the area, and "bridge" every
>> single trace manually, with stripped wire. even the traces that
>> dont show problems. or, replace the board with the newly ran
>> batch.
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>>
*From:* Sam Mims <xxx@xxxxxxx.xxx>
>> *Sent:* Friday, April 20, 2018 10:50 PM *To:* Christian Bickley -
>> Wintersun Project; Analogue Heaven *Subject:* Re: [AH] Korg Polysix
>> MG Rate Knob Issue
>>
>> Are you absolutely sure that every trace in that area of the board
>> is working?  Battery damage usually destroys traces and/or
>> components, and it is easy to overlook one trace among the many
>> that cross through the 'land of corrosion'.  And one damaged trace
>> can lead to strange operation.  I have thought I had a Polysix
>> board all repaired on several occasions, only to have the Polysix
>> act in a very strange way.  Then I would go back and find that I
>> missed one little bit of trace repair.
>>
>> I found it most effective to make a paper copy of that area of the
>>  board layout (from the service manual), and then use a highlighter
>> to color every trace that has tested ok.  Otherwise, it's too easy
>> to miss a bit.
>>
>> Good luck - that type of repair is not for the faint of heart!
>>
>> Sam Mims
>>
>> Syntaur
>>
>>
>>
>>
>> On 4/20/2018 5:38 PM, Christian Bickley - Wintersun Project wrote:
>>> Hi all, ive been painstakingly replacing the dreaded battery
>>> board on my Polysix but ive run into a frustrating problem. When
>>> i turn the MG rate knob it works but in a rather odd way, if you
>>>  have the knob set at 0 and turn the knob clockwise, it will not
>>>  activate the rate of the MG until it gets to about 4 on the pot,
>>> from there the MG kicks in but has an extremely narrow sweet
>>> spot, within two marks on the dial it has gone from zero to full
>>> speed, so its literally uncontrollable, making the full sweep of
>>> the pot pretty much redundant. Can somebody let me know what i
>>> need to look at to sort this out, im going around in circles and
>>> cannot work out where this problem is coming from on the circuit
>>> or more importantly how to fix it. Ive fixed a lot of problems on
>>> this board and other problems on the synth but this part is
>>> really confusing me.
>>
>