Korg Mono/Poly

Hi All

Long time MP4 lover here.. turned it on today after a couple of
months storage and it's virtually silent, till I crank the headphones
loud and then....

when I play keys, I can hear at very low level noise like the "gate"
opening.

The VCA envelope controls shape the envelope of this low level noise.

If I twiddle the filter resonance, I can hear the noisy pot, but no
actual filter resonance.

If I twiddle the filter cutoff I hear nothing, it doesn't filter the
noise.

I can tell the VCO's are receiving trigger because their LED's light up.

*** SO *** looking a the block diagram, I guess I either have a
problem in the "mixer" (post VCO's pre VCF) or in the VCF itself???

Does anyone have an opinion on this??

Any suggestions graciously accepted,,,,,,

peace & sine waves
Simon

p.s. I never even knew there was an MP4 group....

Hi Simon

> when I play keys, I can hear at very low level noise like the "gate"
> opening.
> The VCA envelope controls shape the envelope of this low level noise.

if you turn all four parameters of the VCA-Envelope fully
counter-clockwise. Playing a key you should hear a klick. -> if yes ->
VCA is good and the output socket is good.

Then set
VCA-Envelope to A=0, D=0, S=10, R=10
VCF-Envelope to A=0, D=0, S=0, R=0
VCF Cutoff = 5, Resoncance = 10, Envelope amount = 10(+5)
press a key several times, you should hear a fast resonance
"Zongggg"-like sound.
-> if not -> check the VCF-cutoff-modulation input socket. -> many other
problems tooo... ;-/ (see below)
-> if yes -> turn the cutoff frequency fully clockwise and turn up noise
volume: do you hear noise?
If no ->
If you are keen enough to open up the monopoly (ATTENTION: live
endangering electric power inside!) set the keyboard to hold, press four
notes (or unisono) and check the noise and VCOs signal at pin 1 of
connector 14 (the connector is at the right hand side of the VCO-pcb
between the volumes of VCO1 and VCO2). If you do not have an
socilloscope, the connect the output with an mixer and use the tip of
another cable, connected to the same mixer as signal search (don't turn
up the volume too loud, the signals might kill your
tweeters/headphones/ears).

If there is still nothing to hear I assume that the powersupply is
defect. If there is something to hear, either the cable between VCO pcb
and VCF pcb is broken, or the VCF chip SSM2044 is gone. Sometimes the
2044 is socketed, then you might check whether the chip is seated ok in
the socket. But this requires unmounting the pcb from the frontpanel,
which is not much fun.

Florian

Hi Florian, Thanks man!

I'm enjoying this, nerd that I am.

Indeed can't get the filter to self oscillate audibly as per your
instructions.

There is signal present at connector 14 pin 5 (I seem to have the "new
production" version).
Pin 1 of connector 14 is this great distorted version of the VCO's...
I'll resist the urge to go hotrodding the synth....

anyway...

Got the SSM2044 datasheet.

I have signal at Pin 1 (input) of the SSM2044 - though much lower in
level, though looking at the schematic theres a 33k resistor in line.

But no signal at Pin 3 (output) of the 2044 - totally dead - with the
controls set right.

I've reseated the 2044 and put a bit of deoxit on the pins and cable
connectors but no go.

Seems like the silence at 2044 pin 3 points to a dead filter chip, do
you think????

There are some 2044's on ebay, though some of the other numbers on the
top are different. Do you think that matters????

Thanks heaps for your assistance Florian, really appreciated.
Sime



--- In korg_mono-poly@yahoogroups.com, Florian Anwander
<fanwander@...> wrote:

>
> Hi Simon
>
>
>
> > when I play keys, I can hear at very low level noise like the "gate"
> > opening.
> > The VCA envelope controls shape the envelope of this low level noise.
> if you turn all four parameters of the VCA-Envelope fully
> counter-clockwise. Playing a key you should hear a klick. -> if yes ->
> VCA is good and the output socket is good.
>
> Then set
> VCA-Envelope to A=0, D=0, S=10, R=10
> VCF-Envelope to A=0, D=0, S=0, R=0
> VCF Cutoff = 5, Resoncance = 10, Envelope amount = 10(+5)
> press a key several times, you should hear a fast resonance
> "Zongggg"-like sound.
> -> if not -> check the VCF-cutoff-modulation input socket. -> many

other

> problems tooo... ;-/ (see below)
> -> if yes -> turn the cutoff frequency fully clockwise and turn up

noise

> volume: do you hear noise?
> If no ->
> If you are keen enough to open up the monopoly (ATTENTION: live
> endangering electric power inside!) set the keyboard to hold, press

four

> notes (or unisono) and check the noise and VCOs signal at pin 1 of
> connector 14 (the connector is at the right hand side of the VCO-pcb
> between the volumes of VCO1 and VCO2). If you do not have an
> socilloscope, the connect the output with an mixer and use the tip of
> another cable, connected to the same mixer as signal search (don't turn
> up the volume too loud, the signals might kill your
> tweeters/headphones/ears).
>
> If there is still nothing to hear I assume that the powersupply is
> defect. If there is something to hear, either the cable between VCO pcb
> and VCF pcb is broken, or the VCF chip SSM2044 is gone. Sometimes the
> 2044 is socketed, then you might check whether the chip is seated ok in
> the socket. But this requires unmounting the pcb from the frontpanel,
> which is not much fun.
>
> Florian
>

Hi Simon

> But no signal at Pin 3 (output) of the 2044 - totally dead - with the
> controls set right. [...]
> Seems like the silence at 2044 pin 3 points to a dead filter chip, do
> you think????

Now, still there is a little hope for the 2044. Check the voltage at pin
15 (offset) and pin 13. If it would be -15 Volts, then the VCF would
shut down completely and no other CV would help.

But in fact I fear a dead 2044 too.

> There are some 2044's on ebay, though some of the other numbers on the
> top are different. Do you think that matters????

No. Single SSMs are available from Senso (http://www.vintageplanet.nl/)
for around 17 Euros. The seller "technologytransplant" on ebay sells
good ones as sixpack for 55 Euros!

Florian

Hi Again

> Now, still there is a little hope for the 2044. Check the voltage at

pin

> 15 (offset) and pin 13. If it would be -15 Volts, then the VCF would
> shut down completely and no other CV would help.

Hummm.. do you mean the voltage difference between those two pins?
Or the difference between each of them and ground??

thanks and thanks again

Simon

Hi Simon

>> Check the voltage at pin
>> 15 (offset) and pin 13. If it would be -15 Volts, then the VCF would
>> shut down completely and no other CV would help.
>
> Hummm.. do you mean the voltage difference between those two pins?
> Or the difference between each of them and ground??

I mean difference between each of them and ground.

Florian

Hi Florian

I might of lost something in translation here. This is what I
measuring...

I am referenceing the 2044 datasheet here:
http://www.synthdiy.com/show/?id=86

Setting the multimeter to DC and a range of 20v this is what I have

2044
pin 16 +V = +15
pin 15 SIG IN- = -0.09
pin 1 SIG IN+ = -0.06
pin 9 -V = -15
pin 13 freq ctrl = -0.10 filter knob fully open
= 0.09 filter knob fully closed


Two things confuse me here... the voltage for the signal seems very
low.. and also the Fc ctrl voltage seems low, and yet it responds
correctly to Fc knob, envelope etc.

Looking at the specs, the range is supposed to be 0.6 to 1.5.

However, I don't really know what I'm talking about here. Do you know
??? :)))

thanks again
pot.

--- In korg_mono-poly@yahoogroups.com, Florian Anwander
<fanwander@...> wrote:

>
> Hi Simon
>
> > But no signal at Pin 3 (output) of the 2044 - totally dead - with the
> > controls set right. [...]
> > Seems like the silence at 2044 pin 3 points to a dead filter chip, do
> > you think????
> Now, still there is a little hope for the 2044. Check the voltage at

pin

> 15 (offset) and pin 13. If it would be -15 Volts, then the VCF would
> shut down completely and no other CV would help.
>
> But in fact I fear a dead 2044 too.
>
> > There are some 2044's on ebay, though some of the other numbers on the
> > top are different. Do you think that matters????
> No. Single SSMs are available from Senso (http://www.vintageplanet.nl/)
> for around 17 Euros. The seller "technologytransplant" on ebay sells
> good ones as sixpack for 55 Euros!
>
> Florian
>

Hi Florian

Happy to report that my new SSM2044 arrived from vintage planet in the
Netherlands in record time. Popped it in and all is well. The synth
sounds "new". Really happy.

Thanks heaps for your research and advice, much appreciated!!

Another MP4 lives to squelch another day....

Sime

--- In korg_mono-poly@yahoogroups.com, Florian Anwander
<fanwander@...> wrote:

>
> Hi Simon
>
>
>
> > when I play keys, I can hear at very low level noise like the "gate"
> > opening.
> > The VCA envelope controls shape the envelope of this low level noise.
> if you turn all four parameters of the VCA-Envelope fully
> counter-clockwise. Playing a key you should hear a klick. -> if yes ->
> VCA is good and the output socket is good.
>
> Then set
> VCA-Envelope to A=0, D=0, S=10, R=10
> VCF-Envelope to A=0, D=0, S=0, R=0
> VCF Cutoff = 5, Resoncance = 10, Envelope amount = 10(+5)
> press a key several times, you should hear a fast resonance
> "Zongggg"-like sound.
> -> if not -> check the VCF-cutoff-modulation input socket. -> many

other

> problems tooo... ;-/ (see below)
> -> if yes -> turn the cutoff frequency fully clockwise and turn up

noise

> volume: do you hear noise?
> If no ->
> If you are keen enough to open up the monopoly (ATTENTION: live
> endangering electric power inside!) set the keyboard to hold, press

four

> notes (or unisono) and check the noise and VCOs signal at pin 1 of
> connector 14 (the connector is at the right hand side of the VCO-pcb
> between the volumes of VCO1 and VCO2). If you do not have an
> socilloscope, the connect the output with an mixer and use the tip of
> another cable, connected to the same mixer as signal search (don't turn
> up the volume too loud, the signals might kill your
> tweeters/headphones/ears).
>
> If there is still nothing to hear I assume that the powersupply is
> defect. If there is something to hear, either the cable between VCO pcb
> and VCF pcb is broken, or the VCF chip SSM2044 is gone. Sometimes the
> 2044 is socketed, then you might check whether the chip is seated ok in
> the socket. But this requires unmounting the pcb from the frontpanel,
> which is not much fun.
>
> Florian
>