Korg Mono/Poly

Hi - I joined a while back and posted initially about my dead mono/poly with some suggestions to get tke keys cleaned up first. Well I got distracted by other projects (polysix is near finished) since then but now I'm ready to get back to it. I cleaned up half the key contacts (enough at least to know it's NOT the key contacts) and checked the P.S. voltages - seem okay... but what's happening now - (verified the keys are working - mostly- due to triggering VCO LED's on front panel) is that I just have zero output. I'm guessing it's a bad chip somewhere. When you turn the volume all the way up I can hear a rising and falling soft white noise with key presses. So I'm guessing I'm hearing the VCA circuitry doing it's thing (?) - where would you look next? The VCO circuitry? Suggestions? Or can anyone direct me to a post that might be relevant? unfortunately the archive here doesn't seem searchable (or user friendly really).

Thanks. I hope this is clear enough.

PS - EVERYTHING  in terms of front panel lights/indicators seem to be functioning 100% correctly. So it looks like a lot of the function logic is working.

UPDATE: by tweaking the envelope amount polarity control WAY over I was suddenly able to get some sound - even after tweaking the envelope controls a bit. Though I wasn't able to get and timbral change happening by messing around with other controls apart from frequency, etc... but I was able to get different pitches out of different keys...

UNTIL

then suddenly the mono-poly just started emitting constant (distorted) audio, having entered the UNISON mode on it's own. Key presses affect nothing. Then Key Assign Mode LEDs all dead and buttons unable to control anything.

WEIRD HUH?

I'm not sure where to go on this - i guess look at the key assign circuit... though it could be just a byproduct of something wrong with the CPU?

UPDATE:

okay - apparently the above (last report only) was due to a flakey power supply connection (apologies to alarm - well not that anyone is looking anyway) - so I can live with any extant problems - I need to do a basic alignment per the manual next I guess...


ALSO - while checking the power supply again i managed to blow up Q3 (so stupid) - i shorted it i guess.
Does anyone know if this means I took out the M5230 regulator with it? I guess while i'm replacing Q3 it would be a sensible idea to replace any connected parts (?)

suggestions?
thanks

Hello

On 24.06.16 16:22 , jw_dewdney@yahoo.com [korg_mono-poly] wrote:

> ALSO - while checking the power supply again i managed to blow up Q3 (so
> stupid) - i shorted it i guess.
> Does anyone know if this means I took out the M5230 regulator with it?
Not necessarily

> I
> guess while i'm replacing Q3 it would be a sensible idea to replace any
> connected parts (?)
Ummph, difficult to say. If buyong parts is a big effort (long way to
the next store / online only), then you may order the other transistors
too. Those are penny amounts.

Don't forget, that you may have to readjust the complete synth after
replacing parts in the power supply.

Florian

(its difficult to suppress the thought, that you may replace the
technician...)

hello....

Yes sure. I already did that (bought the parts)...

yes - the technician will be punished.

but he is cheap at least...! :)

thank you

I ordered a M5230-L (i hope it's a fair substitution for the M5230) - i could find NO comparisons between the two anywhere!

On 24.06.16 17:23 , jw_dewdney@yahoo.com [korg_mono-poly] wrote:

> yes - the technician will be punished.

(the masochist says: hurt me. The sadist replies: no!)

> but he is cheap at least...! :)

:-))))

:D

oh great to hear thanks... it's what i ordered.

wow - it was actually very lucky in a way that I shorted one of the transistors in the power supply by mistake... IF i hadn't done that - i wouldn't have removed the KLM376A boatd and discovered that CN35 had cracked and LOOSE solder joints! ALSO - the entire board was CAKED with melted heat sink compound and sticky as hell - i had to bathe it all in alcohol to clean it all off... after i got that done I reflowed most of the solder joints and replaced most of the caps (had a few showing efllurorescence - or 'electrolyte leakage' - so not a bad idea. It turns out I didn't kill any transistors after all.... but rather the fuses (which of course i did not check - it would be too obvious!). Thanks much for your help everyone

Anyway - so the udpate now is I have a FULLY functioning MONO POLY (except for the keys which I will do next I guess)

I have some KaiCote 44... the synthhacker site suggests maybe it's not the best stuff to use (?) any comments on that?