Problem: no sound

JONLIBRA · Post by **JONLIBRA** » Sun Dec 06, 2015 7:43 am

Hello. I have this problem with my K61, no sound from the outputs. It happened at a gig last night, right from the start when i turned on the keyboard. I can hear the sound from the headphones playing from the K keybed and also from the controller, so it's not a keybed issue. Any ideas? Thank you in advance for your help!

Dan Stesco · Post by **Dan Stesco** » Sun Dec 06, 2015 8:30 am

Please check the individual outputs.
Global>Audio>LR Bus Indiv. assign> 1/2 and 3/4.

If your individual assign have sounds and main out not, your audio card need to fix. The mute transistor can be damage. Is happen at Kronos 1 version, when insert or take off the plug until the power cable is connected.
Best,
Dan

JONLIBRA · Post by **JONLIBRA** » Sun Dec 06, 2015 6:25 pm

Thank you, Dan. You're right. I did it and the individual outputs have sound. I guess I need to contact the local Korg service, right? So the problem that you mention occurs when take off the audio plug while the unit is on?
By the way, congratulations for your work!

Dan Stesco · Post by **Dan Stesco** » Sun Dec 06, 2015 7:30 pm

Hi!
I investigate this problem before few years and had a positive feedback from Kronos engineer team. In my situation the outputs have sounds but distorted when the output volume up to 50% . Is happen on Kronos 1. The Kronos X and Kronos II not have this problem.
For Kronos 1 customer:
Please remember that plug the Outputs, Inputs Jack before plug the power cable. Also disconnect the power cable before take of the plugs.
The damage of device of mute circuit will be occurred by inserting plug under the condition of KRONOS that is turning ON.

Call your local KORG service and change the part to KLM-3005 if you have the following service parts.

200129603005 PCB ASSY KLM-3005/6/8/9 KRONOS X-61
200129613005 PCB ASSY KLM-3005/6/8/9 KRONOS X73/88

Best regards,
Dan

JONLIBRA · Post by **JONLIBRA** » Mon Dec 07, 2015 4:25 am

Thanks, Dan!

I"ll follow your advice.

AntonySharmman · Post by **AntonySharmman** » Mon Dec 07, 2015 11:22 am

BTW , here are some technical details concerning this issue that might help some of you !

Output distributor Board of Kronos KLM 3005 uses in all outputs the muting transistor 2SD2704 of 20v breakdown voltage limit
in DC coupling with output jacks and also this conjunction uses a anti-parasitic induction coil in series that can dramatically
raise reverse voltages applied to that transistors when strong electromotive force of 50-60 Hz is applied from stage console
or any external preamplifier device that can easily destroy them due to insufficient grounding of electricity net power supply !
A sufficient electronic protection for this could be the adding of a no-polarity 100μF capacitor in series in every output circuit.

Therefore even replacing those transistors or KLM 3005 module this will not prevent from a future destruction under those
circumstances , so always test if small surface electric hazards are noticed between jack cables of those equipments and your
Kronos chassis in gigs or at your studio and do not connect them in Kronos outputs before this grounding issue has been settled !

JONLIBRA · Post by **JONLIBRA** » Tue Dec 08, 2015 4:32 am

Thanks, Antony!

Interesting information to keep in mind. I was using a Ups at the gig but clearly that wasn't enough protection...

Best,

dfahrner · Post by **dfahrner** » Tue Dec 08, 2015 6:23 am

Could somebody clarify this? The way I read it, the problem happens when the AC power cables of the KRONOS and whatever device its signal outputs are to be connected to do not have a common ground connection, and there is a voltage difference between the two AC gounds...then when the KRONOS signal output is connected to the other devices input, this voltage difference (plus possible voltage generated by induction coils) can destroy the muting transistors...is that right?... so as long as the KRONOS and the device that its signal outputs are connected to (mixer, powered speaker, etc.) are connected to the same AC source (the same wall plug, UPS, power block, etc.) then there's no problem, and the signal connections can be made either before or after the power connections...???

df

AntonySharmman · Post by **AntonySharmman** » Tue Dec 08, 2015 3:08 pm

OK then , I'll try to make it more clear but still some electronics knowledge is required here.

When two different outlet supplies (common ground is by definition) like outlets of stage
equipment and main console , introduce a significant voltage value between their common grounds
that is not close to zero as required , then this means that an intermediate device
(like stage lights,compressor motors) absorb a lot of power and the weak net grounding balance
is disturbed with current leakage forwards ground with consequence different common ground
points of net supply to point a significant voltage difference , or raised voltage difference between
outlet ground and physical ground that can be practically noticed with skin surface electric hazards
between let's say jack ground and metallic chassis of your keyboard when it's connected to main
power (joined to ground circuit).

This 50-60 Hz EMF voltage can easily destroy a low voltage device like an output when it's DC
coupled like in the following circuit of Kronos output when is directly connected there.
The circuit can close there neither with jack ground nor with UPS common ground but the particular
mute transistors need a control voltage in order to contact and absorb that current as dump loads
and this voltage is applied only when PSU is turned on , that's the explained previous reference
of Dan about power supply caution !

People with knowledge in electronics can make their conclusions with the above schematic diagram of K outputs

All audio equipment PSUs , even UPS systems always connect earth net ground to common sound signal(-)
so it's always active.
Let's say that a low efficiency precaution is to connect output jack before turning Kronos power on , but still not safe !
The only easy and feasible way to prevent sensitive inputs/outputs from this parasitic ground
differential voltages is the low Z isolated transformer line transmission that a DI box (or some
keyboard outputs) provide , where you can safely lift ground connection and regulate this phenomenon
in a gig where you're not involved , but as concerning to your home studio , this weak net grounding
must be corrected !

Hope this might help some of you !

JONLIBRA · Post by **JONLIBRA** » Tue Dec 08, 2015 5:05 pm

Thank you very much, Antony.

Do you know if Kronos 2 is safe on that regard?

AntonySharmman · Post by **AntonySharmman** » Tue Dec 08, 2015 6:18 pm

JONLIBRA wrote:Do you know if Kronos 2 is safe on that regard?

I do not own yet a service manual of Kronos 2 , but I don't think they had any reason to change output circuit
since it's already very well designed , this issue when happens has to do with any sensitive audio equipment pre-amp
output stage (DC coupled) when transferred via open line and I've overestimated its magnitude on purpose , not in
order to terrify you but instead to show you the results of worst scenario of this case that already had happened to Dan
and maybe also to You.

BTW previous output stage diagram and my reference is for Kronos X (same circuit with older Kronos) ...

Dan Stesco · Post by **Dan Stesco** » Tue Dec 08, 2015 8:02 pm

JONLIBRA wrote:Thank you very much, Antony.

Do you know if Kronos 2 is safe on that regard?

I understand that Kronos X and Kronos II not have that problem.
Also if change the Kronos component with Kronos X component the problem are solved permanently.

JONLIBRA · Post by **JONLIBRA** » Tue Dec 08, 2015 8:05 pm

I understand, Antony. So it´s best to use a di box at the gigs...

JONLIBRA · Post by **JONLIBRA** » Tue Dec 08, 2015 8:11 pm

Dan Stesco wrote:
JONLIBRA wrote:Thank you very much, Antony.

Do you know if Kronos 2 is safe on that regard?
I understand that Kronos X and Kronos II not have that problem.
Also if change the Kronos component with Kronos X component the problem are solved permanently.

Ok. I will ask this to the local Korg service.

Thanks again, guys, this forum is awesome!

AntonySharmman · Post by **AntonySharmman** » Tue Dec 08, 2015 9:36 pm

Dan Stesco wrote:I understand that Kronos X and Kronos II not have that problem.
Also if change the Kronos component with Kronos X component the problem are solved permanently.

I will repeat once more ... this is not a Kronos issue , the real issue has been already explained !