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Trouble with a Korg Ps 3100 ! Any techs around?

Posted: Sun Jun 17, 2007 9:49 pm
by ultima
Im having trouble with my Ps 3100.

1 . Three notes "b,c,d#" in the top octave don´t produce a sound , I have checked the keys and they are fine , the fault is definitely not the keys.
2. Whenever I switch the release from damped to half or full the A below middle C starts to creep in and does not stop until i switch back to damped mode, it does however stop momentarily when i press the actual A note but then slowly starts to creep in again. I do not need to press the note at all for it to creep in in the first place.
3.Sometimes i can hear the MG 1 LFO leaking into the audio path. I can hear the oscillations of the LFO even though its not engaged,its a sort of whine that rises in pitch as I increase the speed, faulty cap somewhere?

Can someone with a ps 3100 tell me if the LFO leaking is normal, could be as its an old design ?
I have heard of someone who recapped the whole synth but id rather not unless its needed.
Anyone have the Service manual for this synth or know where I can find one?

Its pretty complicated to track stuff down on this synth due to its Polyphonic nature but im having a go at it.
I wonder if problem #1 is related to the Gate unit or whether its got something to do with the octave divider ?

I´m located in Iceland and there are no keyboard techs over here so Im going to have to sort this out myself, any help would be appreciated.


p.s How can one see/measure if a cap has lost its value?

Posted: Sun Jun 17, 2007 10:01 pm
by pulse_divider
9 out of 10 problems on the PS series are caused by the edge connectors, which get brittle over time and crack in the middle. This causes them to bow outward and lose contact on the middle pins.
Try removing the front panel and carefully inspect all edge connectors for signs of this.
If you need replacements (and you eventually will), Mouser sells them as part # 587-306-50-022
As far as I know, there is no readily available full service manual for the PS-3100 amongst the usual internet sources and analog fans. The best I have seen are really crappy copies of schematics.
Good luck.

Posted: Mon Jun 18, 2007 2:08 am
by ultima
I took off the front and yes the connectors are obviously damaged.
I took out all the cards and tried a little glue on the connectors but no change..
It seems to change its behaviour a bit when i nudge the cards a bit, but no nudging will affect the problems i had before.

As far as i can tell all the pins are in contact with the PCB ?

Any other ideas?

Thanks for your advice , i´ll definitely need to change those connectors im just not sure its causing the problems.

Posted: Mon Jun 18, 2007 7:02 pm
by ultima
Im still looking for help here if anyone would be so kind?

The current problem with the synth is that when release is set to damped the A below middle C seems to sound different then other notes as it seems to react differently to decay settings on the envelope generator. And when Release is set to Half damped or Release that same note acts as its stuck i.e doesnt stop sounding until i switch back to damped mode. Maybe its always stuck and i just cant hear it when the release is set to damped?

I also have three dead notes in the top octave but one thing at a time ...:)

I have cleaned up all the edge connectors and made sure that they all work as they should, but still have the same problems.
Im now 99% sure its not the connectors.

Im going a bit nuts here so if anyone has suggestions on where to look for the fault ?
Im no electronics genious but i have patience and a scope and have fixed things before.

Would you suspect the Gate unit or the Signal generator ? I dont find it likely that the fault is in the Control units but im not sure.

Is it safe to swap the gate cards around and see if that changes things??

-- -- --------------------------

update .
I swapped the gate cards around and the fault follows the card.
That means the card is broken on the one note......
Bad op amp ? Bad Cap? Bad transistor ?

Any ideas what to do?

Posted: Mon Jun 18, 2007 10:47 pm
by ultima
In case anyone´s interested or can help , here´s an update.

Im starting to suspect the VCA for the stuck note, Is the VCA controlled by the MC14007b IC on the Gate Board? Anyone know?
Im tempted to replace that IC just to see if it works? If i can find an IC like that ?

If that turns out to be right my next step wold be to replace the same IC´s on the other Gate Card where i have 3 notes not playing.

Feel free to chime in with opinions :D

Posted: Tue Jun 19, 2007 3:32 am
by Maschinengeist
I replied to your email.

As stated in my email, I don't personally suspect the VCA... at least not at this point.

From all you're describing here, the poor PS 3100 needs to see a synth doc for a global check up. Not implying that it's imperative but you'll have a lot you check after - my modest opinion.

Posted: Thu Jun 21, 2007 12:50 am
by ultima
does anyone have the service manual for the PS 3100?