Yahoo Groups archive

Vintage Synth Repair

Index last updated: 2026-04-28 23:41 UTC

Thread

Korg SQ-10 - wavering in pitch...

Korg SQ-10 - wavering in pitch...

2013-11-05 by <noddyspuncture@...>

Hi guys,


I have a Korg SQ-10 sequencer here that has been playing up. It was acting up a while ago but after I looked at it and then put it back together, it seemed OK for a while. That led me to suspect a dodgy connection or a dry joint... but I'm now discounting that as I have been pressing on different parts of the circuit and moving connectors and it stays faulty. So I am assuming component failure.

The symptoms are a wavering and very unsteady/un-solid pitches on steps 2 > 12 on all three channels - A, B and C.

Strangely though, step one is solid (on all channels)..! I have examined the schematic and there does seem to be a step that has a unique path - but that seems to be step 12, not 1..!

To date I have changed IC H (4066) and also IC D (LM324N) but all symptoms stay the same.

I am fast running out of ideas... but think that surely the fact that step 1 is solid, is pointing somewhere...!?

Cheers,
TOM

RE: Korg SQ-10 - wavering in pitch...

2013-11-06 by <wmc_mick@...>

I'm in the process of repairing a Crumar Composer and I have found some bad traces on the pcbs, bad ic sockets and dry solder joints. When you say the symptoms are what they are I really suspect bad connections since the Crumar acted the same (unstable cutoff-frequency, resonance etc). I found some bad connections by pressing the pcbs at different points but some signals I had to trace with an oscilloscope to find.

Obvoiusly the problem is due to something that all steps 2 > 12 have in common, power lines come to my mind, would it be possible that one of the power lines goes bad due to break in trace or something else after the circuitry for step one? I have had that kind of problem with polyphonic after touch on a master keyboard where seven keys did not send after touch due to a cut in the common power line for eight keys.

- Mick

Re: Korg SQ-10 - wavering in pitch...

2013-11-06 by scott frye

If any of the ICs in the signal path are socketed, I would CAREFULLY pull each and buff the leads with some 1000 grit wet sanding paper ( only dry)

--
Scott Frye

Audio-fixation.net

Vermont

RE: Korg SQ-10 - wavering in pitch...

2013-11-06 by <noddyspuncture@...>

Thanks for the tips guys.


The power supply idea was the first that occured to me... but the way it's laid out on the main panel with the 12 separate circuits for the steps... step 1 is actually the farthest from the main power supply input!


Also, the only socketed IC's are the two I have just changed. Do any of you have the schematic?


I was wondering if anyone could advise as to where, apart from the main board with all the pots, I should be looking for somewhere, as mentioned by Mick, where the 12 steps 'separate' and could be individually affected. Each step has it's own 4007 IC... but I can't really see 11 of them going faulty at once...!?


Cheers,

TOM



---In vintagesynthrepair@yahoogroups.com, <painintheamp@...> wrote:

If any of the ICs in the signal path are socketed, I would CAREFULLY pull each and buff the leads with some 1000 grit wet sanding paper ( only dry)

--
Scott Frye

Audio-fixation.net

Vermont

Re: [vintagesynthrepair] RE: Korg SQ-10 - wavering in pitch...

2013-11-06 by Tom Butcher

In general, is the 1000 grit sandpaper the best way to clean ICs? I have an Oberheim DMX project I'm working on, and the boards and chips are all super dirty. I thought I would take everything out of its sockets and spray the lot down with DeOxit.
Show quoted textHide quoted text
On Wed, Nov 6, 2013 at 1:54 PM, <noddyspuncture@...> wrote:

Thanks for the tips guys.


The power supply idea was the first that occured to me... but the way it's laid out on the main panel with the 12 separate circuits for the steps... step 1 is actually the farthest from the main power supply input!


Also, the only socketed IC's are the two I have just changed. Do any of you have the schematic?


I was wondering if anyone could advise as to where, apart from the main board with all the pots, I should be looking for somewhere, as mentioned by Mick, where the 12 steps 'separate' and could be individually affected. Each step has it's own 4007 IC... but I can't really see 11 of them going faulty at once...!?


Cheers,

TOM



---In vintagesynthrepair@yahoogroups.com, wrote:

If any of the ICs in the signal path are socketed, I would CAREFULLY pull each and buff the leads with some 1000 grit wet sanding paper ( only dry)

--
Scott Frye

Audio-fixation.net

Vermont




--
Tom Butcher

Re: Korg SQ-10 - wavering in pitch...

2013-11-07 by scott frye


De-oxit is helpful but something else needs to contact the leads to remove oxides and such.

Laying down an IC on edge so that all the pins on one side can be polished with a piece of superfine grit wet-sanding paper is one way.

An artists eraser , the type that looks like a pencil , is another way to "polish " the IC pins . It's just more work.
--
Scott Frye

Audio-fixation.net

Vermont

Move to quarantaine

This moves the raw source file on disk only. The archive index is not changed automatically, so you still need to run a manual refresh afterward.