Korg Forums

richie1027 · Joined: 09 May 2011 Posts: 23

Hey all.".".........this re a 73 key M50 very lightly used an in studio only. Haven't touched in 7 months and when I powered up, sound from L&R was barely audible and scratchy.
1. Changed cables
2. Changed amplifier

Next I ran cable out from headphone jack and I got sound but very low. I reinitialized the system and tried and still no go. Output can be heard but only with volume on full, both on Korg and with amp.

Some old post mentioned striking the low keys repeatedly but that didn't sound to reliable.

Anyone else experience this? Any suggestions shy of taking it to a service center? Thanks
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Gear:
Motif XF7 w/FC7 pedal
Korg M50 w/Exp-2 pedal
Yamaha MX61
MicroKorg
Roland KC 500 & 110
Yamaha Stagepass 500
Lotsa extras...

GMUL · Joined: 21 Mar 2011 Posts: 25

I think responses and interest in the m50 are few and far between. My advice would be buy another keyboard. The m50 has inherent flaws that korg know about but won't offer solutions to.

KeyBones · Joined: 28 Apr 2015 Posts: 3

This is exactly the problem I had with mine. Solved by re-soldering the three capacitors on the output board. Was a cold solder joint problem.

valentenet · Joined: 05 Aug 2015 Posts: 3 Location: Brazil

I have the same problem.
I had the same problem. Suddenly, when playing, the sound stopped. When I turn it on I can hear a initial hisss.
I open the keyboard and I found that the sound still coming from the main board (the cable that pass through the volume potentiometer).
In the audio block at the same board where are the midi and power supply, I tested the amplifier CI (NJM4556A) between the audio in and the output jacks.
I know by it´s datasheet (NJM4556A) that it should be something around -10volts at the pin nunber 4 and +10v at the pin number 8 to it works. But I found just 0.23v at the pin 4.
Taking a better look at the board and following the trails I just find a conection to the main board together to the power cables. I don´t know if the necessary power is feeded by the main board to activate the CI or if is from the power block.

I am not a Technician, just hobbyist and autoditact. I think if I get the Circuit Board Schemes I can discover more information.

The good news is that it´s possible in this case, feed pin 4 the CI from another power source or discart this part of the board and instal a DIY pre-amplifier between the audio in and the jackets.

If someone has this boards schemes, please let me know.

image of comments at: https://picasaweb.google.com/lh/photo/pZJaTVS0HP2UsAOT0nx1No5cq3mb_jJRTAjvUm_rMYE?feat=directlink
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VALENTENET
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Vintage Electromechanical Pianos works

Pianet T | Pianet N | Piano Suette (big series) | Piano Suette (compact series) | Hammond XB3 | Korg SV173 | Casio PSR 550 | M-Audio Axion 61

valentenet · Joined: 05 Aug 2015 Posts: 3 Location: Brazil

I found it! The diode (D4) is flashing. He broke again, it must be with crack, something.
I want to change it but have no idea of their specification. I tried every way to get him Circuit Board, but without success.

I read in the datasheet it is a SCHOTTKY, but do not believe it to be a zener or something very specific. I know he's working gives an impedance of 660ohms (when I put the miter diode test option he gives 580).

I have a lot diodes similar to those in other scrap plates here with similar reading both model (without terminals) as terminals.

Algue know more information about this diode? If I can just substitute one for the other?

Does anyone have the circuit diagram of it? Manual or services?

I have attached as a reference a card I used to talk in the forums with datasheet cue circuit (right next to the board) and voltage readings on the outputs of the IC and the diode is good and when it fails.

https://picasaweb.google.com/lh/photo/4xa_IJ0lHSqS7Z1EhfK5rdMTjNZETYmyPJy0liipFm0?feat=directlink
_________________
VALENTENET
_________________________________
Vintage Electromechanical Pianos works

Pianet T | Pianet N | Piano Suette (big series) | Piano Suette (compact series) | Hammond XB3 | Korg SV173 | Casio PSR 550 | M-Audio Axion 61

valentenet · Joined: 05 Aug 2015 Posts: 3 Location: Brazil

Sirs, I found the information I was looking for at the link below:

http://www.dtforum.info/index.php?topic=128457.0
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VALENTENET
_________________________________
Vintage Electromechanical Pianos works

Pianet T | Pianet N | Piano Suette (big series) | Piano Suette (compact series) | Hammond XB3 | Korg SV173 | Casio PSR 550 | M-Audio Axion 61