kawai sx-210 Square wave faulty

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cutoffres
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kawai sx-210 Square wave faulty

Post by cutoffres » Tue Jul 12, 2011 4:20 pm

Hello to all ,
I've got a kawai sx 210 , after restoring some analog circuits it is almost full working except one thing :
There'is no square wave .
I think square wave is digitally generated, but how ?

So my questions are :
-What are the integrated circuits and digital chip that generates the square wave ?
-Where will you search first, knowing that there is no square wave on none of the voice ?
-how get square wave back to work ?

Service Manual is here :
http://recybot.free.fr/documents/sx210_SM.pdf

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Re: kawai sx-210 Square wave faulty

Post by th0mas » Tue Jul 12, 2011 5:19 pm

(I'm coming off a success finding a dead op-amp on a TR707 last night, but might be totally off base)

So I glanced at the document.

By square wave you mean pulse width right?

Looks like the PWM output for every voice is generated from the DCO sawtooth and the sample & hold generator.

The relevant page of the service manual looks like the one marked -47- (PDF page 16)

Since it doesn't work for any of the voices, but the DCO otherwise works, I'm guessing it's the sample & hold generator.

So, check the sample & hold generator output with a scope (or maybe with headphones to hear clicking if you have no scope). That would be I13, pin 13. It should be the sample & hold output.

Disclaimer: I could be 100% wrong

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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Tue Jul 12, 2011 6:21 pm

Hi thomas, and thanks for the time you took .
th0mas wrote:By square wave you mean pulse width right?
Yes i mean PW : when PW is alone and PWM level at 00 there is no sound from the PW .

Else works good : Sine wave sound , PWM sounds .
So you could be right.


th0mas wrote:Since it doesn't work for any of the voices, but the DCO otherwise works, I'm guessing it's the sample & hold generator.

So, check the sample & hold generator output with a scope (or maybe with headphones to hear clicking if you have no scope). That would be I13, pin 13. It should be the sample & hold output.
So, If i understand well, you mean that l13 could be faulty, ?
or it could have a bad trace between l13 (4051) pin 13 and l20 (TL082) ?
or it could be l20 (TL082) itself that is faulty ?

Do you think i am on the good way ?
Thanks a lot Thomas

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Re: kawai sx-210 Square wave faulty

Post by th0mas » Tue Jul 12, 2011 10:15 pm

lol wait when PWM is at 0 you get no sound? But when PWM is any other value it works?

It depends on the synth architecture but if that's the case your synth works fine, don't open anything, hahaha

Image

PWM of 0 means the width of the pulse, is 0. as in, no signal. just silence.

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Re: kawai sx-210 Square wave faulty

Post by nathanscribe » Tue Jul 12, 2011 10:19 pm

If that's right, it may be designed in - the Korg MS-10 has zero pulse width at max PW on the knob, which means you can listen to external audio inputs without having the oscillator audible (there's no separate volume for it).

This is pure conjecture as I've not used the Kawai.

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Re: kawai sx-210 Square wave faulty

Post by RetroSynthAds » Wed Jul 13, 2011 4:43 am

Howdy cutoffres and others,

Just so we are all on the same page, the SX210 has three wave forms - Sawtooth, Square Wave, and Pulse.

On my machine... <---- covers my butt :)
... the square wave and pulse are kinda connection - only one can be active at a time.

There is a PW/PWM button beside the Square and Pulse buttons. That one button has two different functions, depending on whether Square or Pulse is active.

When the Square Wave button is pressed, and the PW/PWM button is activated - then you get Pulse Width control of the Square Wave. When the increment dial is set at 0, you get a square wave, and as you move up to 99 you get more pulse.

When the Pulse button is pressed, and the PW/PWM button is activated - then you get Pulse Width Modulation control of the waveform from the LFO. When the increment dial is set at 0, there is no LFO modulation, and as you move up to 99, you get more modulation of the pulse.

Users manual http://www.kawaius-tsd.com/OM/K_SYNTH/SX210.pdf

Page 12:
PW/PWM (Pulse Width/Pulse Width Modulation
- With the square wave; when the pulse width is changed, the tone (timbre) will change
- With the pulse modulation the pulse width will change at the rate set by the LFO. Depth of pulse increases as the value is incremented.

Page 24:
- image of square wave - is called a squarewave. The squarewave used in conjunction with the pulse width control will allow you to control the odd harmonic content and lends itself to create woodwind voices such as clarinet
- image of pulse wave - is called a pulsewave, and can be used alone or with the LFO to modulate the harmonics.

So, later, you say...

"Yes i mean PW : when PW is alone and PWM level at 00 there is no sound from the PW"

...are you saying you are getting no sound when Square Wave is selected, and the PW/PWM increment is at 00 - ie: a full square wave is being produced?

Or, are you getting no sound when Pulse is selected, and the PW/PWM increment is at 00 - ie no LFO is being applied to the Pulse wave?

I think you answer could affect where th0mas points you to in the service manual... :)

Hope I'm not confusing things...
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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Wed Jul 13, 2011 9:21 am

Hi and thanks for the answers

RetroSynthAds wrote:When the Square Wave button is pressed, and the PW/PWM button is activated - then you get Pulse Width control of the Square Wave. When the increment dial is set at 0, you get a square wave, and as you move up to 99 you get more pulse.
Yes, mine is faulty. Because on my sx210, when Square wave is pressed ON and PW/PWM is activated with increment dial at 00 : I have no sound when i should have a pure "square wave"

Now i hope it is clearer ? :mrgreen:

So l13(4051) is still a good candidate for the failure ? Other opinions ?


Again the service manual if you've got a minute :
http://recybot.free.fr/documents/sx210_SM.pdf
Thanks a lot

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Re: kawai sx-210 Square wave faulty

Post by computron » Wed Jul 13, 2011 3:04 pm

Yes, mine is faulty. Because on my sx210, when Square wave is pressed ON and PW/PWM is activated with increment dial at 00 : I have no sound when i should have a pure "square wave"




you will not have a pure square wave with pw or pwm set to zero..You also should not have a slient sound with the pw or pwm set at zero at all .Does the LFO when active respond to shape change?Can you get a square with the LFO?
pw and pwm on both the sx210 and sx240 can seem hardly noticable at times be it at 2 or 78 .
Last edited by computron on Wed Jul 13, 2011 4:00 pm, edited 1 time in total.
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Re: kawai sx-210 Square wave faulty

Post by RetroSynthAds » Wed Jul 13, 2011 3:21 pm

computron wrote:you will not have a pure square wave with pw or pwm set to zero..
Sorry - I shouldn't have said 'pure' square wave. Maybe as square as the sx210 allows? :)

Or, was I totally mistaken in my understanding of the functionality of the square/PW functionality?
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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Wed Jul 13, 2011 4:26 pm

#-o
You successfully lost me :lol:

The problem on my SX210 is that there is no sound when Square wave is ON and PW/PWM set to 00.
I'm pretty sure it is not normal, according to the owner's manual and others SX210 users.

RetroSynthAds wrote:Or, was I totally mistaken in my understanding of the functionality of the square/PW functionality?
Yes i think you're right, but a 100% working sx210 user's will tell us for sure.


computron wrote:You also should not a a slient sound with the pw or pwm set at zero at all
So i'm right, the square wave is faulty ; Cause i should ear square wave with only square wave ON and the PW/PMW set to 00 ?

computron wrote:Does the LFO when active respond to shape change?Can you get a square with the LFO?
Yes square wave on lfo works.

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Re: kawai sx-210 Square wave faulty

Post by th0mas » Wed Jul 13, 2011 5:33 pm

cutoffres wrote:
So l13(4051) is still a good candidate for the failure ? Other opinions ?
No if PWM works then that part is not a good candidate.

Sorry about the confusion about the synth architecture. I should have figured that out before my initial post.

Another question regarding synth architecture: is the squarewave the sub oscillator (1 octave below)?

Reading the last paragraph in the section titled "PULSE WIDTH AND SUB OSC" leads me to suspect the part 4013BE or it's surrounding resistor, diode, and condensor.

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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Wed Jul 13, 2011 5:47 pm

Yes, sub oscillator is squarewave 1oct below.

That'is why i suspected a bad trace, cause sub osc works.

Still inspecting the service manual but i don't find the problem origin, cause for me polysynths with dco architechture are really harder to understand than a single vco monosynth.
#-o

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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Wed Jul 13, 2011 9:15 pm

Also, I wonder if anyone can explain how is generated the square wave and what is the squarewave signal path on the Kawai sx 210 ?

service manual : http://recybot.free.fr/documents/sx210_SM.pdf

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Re: kawai sx-210 Square wave faulty

Post by th0mas » Wed Jul 13, 2011 9:41 pm

I no longer have an idea. Don't listen to me. My suggestion was because I thought sub osc was what was broken.

Good luck :)

Tom

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Re: kawai sx-210 Square wave faulty

Post by cutoffres » Fri Jul 15, 2011 8:58 am

Ok, thanks Tomas ! :D

So, i recall the problem :

on the kawai sx 210 there is 3 waveforms on the DCO : Sawtooth, Square Wave, and Pulse.
On mine, everything works except Square wave : no sound . Square wave works for modulating lfo and others ...But do not sound on the dco section .
So where to find ? What would be the IC involved in the square wave generation ?

Here is a copy of the service manual :

http://recybot.free.fr/documents/sx210_SM.pdf

Thanks to all techs !

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