Need Assistance with curious problem with Kawai K1r

Thread Starter

lahatte

Joined Jul 26, 2017
5
I recently got a Kawia K1r synth sound module. It would not retain program memory after unplugging, so I replaced the wired battery with a battery holder to make future battery changes easy. The synth worked fine, but still no memory retention. So I checked and found I had a bad solder joint on the holder. Fixed that, now memory is retained.

But... now for some reason I have no audio output on the rear jacks (left and right channels), but the headphone jack on the front does have audio.

With the help of some very good people at the Gearsluts forum I have been able to determine that the output muting transistors are not getting shut off. See the attached schematic of a similar unit (K1m). The two muting transistors are Q2 and Q3. Q4, as I understand it, is supposed to get turned on, and pull its collector low, and thus turning off the two muting Q2 and Q3. But I don't read any power at Q4. But then I don't seem to be able to read powr at several places that should show something. For example, where the ICs say VDD on the schematic I can't seem to get any voltage showing on my multi-meter.

Also, I don't get why on my multi-meter I get -34.4mV on one end of the fuse and -4.4mV on the other end. Surely this should be at least 5V or something? Of course, if I remove it the unit will not power on, so it's obviously working. Power is provided to the unit via an external 12V power supply (wall wart)

I would appreciate some assistance on this. A service manual is attached. See the K1m schematic.

Thanks.
Clay
 

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MrChips

Joined Oct 2, 2009
30,720
First things to check are your supply voltages.
Check the voltages on the 7808, 7805 and SI-8201L voltage regulators.
 

Thread Starter

lahatte

Joined Jul 26, 2017
5
I will try to look at those. But so far I have found that pin 6 on IC15 is not sending out voltage. If I jump pin 5 (VDD) and pin 6 the unit works as normal, with audio at the rear jacks.

IC15 is getting VDD on pin 5. I can't get a voltage reading coming in on pin 3 from IC20. I don't know what that IC20 pin 3 output is supposed to be at this point. Is it a voltage or a pulse? I'll have to look for the datasheet for that one.

This is the IC15 datasheet by the way...
http://www.ti.com/lit/ds/symlink/cd74hc4538.pdf

Also, I was informed that the fuse is on the ground side, so that explains the no voltage reading on it.
 

MrChips

Joined Oct 2, 2009
30,720
I will try to look at those. But so far I have found that pin 6 on IC15 is not sending out voltage. If I jump pin 5 (VDD) and pin 6 the unit works as normal, with audio at the rear jacks.

IC15 is getting VDD on pin 5. I can't get a voltage reading coming in on pin 3 from IC20. I don't know what that IC20 pin 3 output is supposed to be at this point. Is it a voltage or a pulse? I'll have to look for the datasheet for that one.

This is the IC15 datasheet by the way...
http://www.ti.com/lit/ds/symlink/cd74hc4538.pdf

Also, I was informed that the fuse is on the ground side, so that explains the no voltage reading on it.
You stated in your initial post that you were not getting 5V power at VDD. That is why I suggested checking the voltage regulators first.

IC15, CD74HC4538 is a monostable multivibrator. It requires continuous pulses on pin-4 in order to keep it triggered (pin-6 must stay high at +5V).
Also IC20 pin-3 flip-flop output must be continuously high, otherwise IC15 pin-6 will go low (0V).
 

Thread Starter

lahatte

Joined Jul 26, 2017
5
I can't find any info or datasheet for a chip on the board of a Kawai K1r. The chip is labeled KTG002 tone generator in the service manual. There is a pin labeled "SD". What might that be? This sends some kind of signal to a multivibrator (74HC4538) which is used to send a signal to turn off muting transistors for the audio outputs on the rear panel.

See the attached service manual, page 7.
 

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IMP002017

Joined Jan 28, 2017
192
I am not sure. It could be a couple of things off the top of my head

Shut Down

However I did work on a Car stereo with an SD that was for Signal Input. So I would guess without much look at the Schematics that it might be for Shut Down. However I am sure someone will correct me...

For when I last worked with a Shut Down it was if Pulled low it would be off if High it would be on if I remember right...
 

absf

Joined Dec 29, 2010
1,968
The signal "SD" also goes to the inputs of IC12 & IC13's "SI" pins. So let me guess, SD may stand for Serial Data and the SI is Serial Input of the Digial to Analog Converter.

Did you see the signal with a scope? It should be a train of pulses when something is playing....

Allen
 

MrChips

Joined Oct 2, 2009
30,720
SD stands for Serial Data.

Look at IC20, HC107.

Get a voltmeter and measure the voltage at pin-3 and pin-13 with respect to GND.
Both should be at 5V. If pin-3 is at logic LOW then IC15, HC4538 will be sending LOW on pin-6.
 
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