Capacitor replacement for a Korg m50 gone wrong

Thread Starter

sull1372

Joined Mar 6, 2019
9
Hey Guys,

I'm fairly new to soldering but i make it work. I've fix many music keyboards and replaced potentiometers, faulty buttons and a few capacitors. So i'm curious how some one would approach this. I bought a broken korg M50 with the intention of fixing a capacitor that fails on roughly 1/2 of this model. Korg provide the instructions to do this. When I took the Main board out of the keyboard i was saddened to find out that some one had tried to do the repair ( a very poor job at that ) and damaged or burnt part of the main board. I have attached a picture and the schematic. Can I save this? it looks like R28 had been re-soldered on the bottom. Capacitor C37 was completely missing. it looks like the contact pad had been pulled off too ( or is that how its supposed to look?) can anyone help please? thank you.

korgm50.jpg
m50mainboardscematic.png
 

Yaakov

Joined Jan 27, 2019
1,601
Can you take a picture that shows more of the surrounding area on the board? The schematic isn't corresponding, or I am not seeing how it corresponds. The schematic suggests the keyboard should work even without C37 in place, but be noisy.
 

Thread Starter

sull1372

Joined Mar 6, 2019
9
Sorry here is the main board schematic again as a PNG file. The JPG i provided was compressed and indistinguishable.

**Correction it looks like the forum upload center is lowering the resolution of the file . let me know if what i sent is helpful I can send more. **
 

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Thread Starter

sull1372

Joined Mar 6, 2019
9
The keyboard will power on. Backlight will be on but the screen will stay blank. It will not progress to the boot sequence so no sound is produced when hitting the keys. Pretty much exactly what korgs repair memo explains. its a simple capacitor swap to fix it. Do the pads look ok from where the capacitor had been removed? C37
 

Yaakov

Joined Jan 27, 2019
1,601
The keyboard will power on. Backlight will be on but the screen will stay blank. It will not progress to the boot sequence so no sound is produced when hitting the keys. Pretty much exactly what korgs repair memo explains. its a simple capacitor swap to fix it. Do the pads look ok from where the capacitor had been removed? C37
The linked bulletin doesn't describe those symptoms. In that bulletin, there are messages on the display. Is it the wrong bulletin?
 

Thread Starter

sull1372

Joined Mar 6, 2019
9
My issue is the 3rd bullet point.

Problem

Some M50 series keyboards suffer from an issue that may cause the following symptoms:

  • A short time after being turned on, the Front panel switches stop working.
  • Every time the M50 is turned on, it displays "Updating Right Panel" followed by "Updating Left Panel", and finally "Completed. Please turn the power off." The unit never boots into the normal play mode.
    *** Important Note *** If the display indicates "Error updating the panel" instead of "Completed", then the issue is due to a problem with one of the front panel boards, and the rest of this bulletin does not apply. Check the last panel that was being updated before the error message was displayed. It may be a simple loose connection between the main board and the panel PCB, or a problem with the key scanning chip on the panel PCB.

  • The M50 freezes at start-up. Possibly with a blank screen.
 

Yaakov

Joined Jan 27, 2019
1,601
The last is far too vague. You have a seriously cratered board. I suspect your lack of display is related to something much more severe.

You should measure the 18V rail that cap was connected to and see if it is alive. If it is, you can try running jumper wires to replace the burnt pads, by following the schematic and looking for continuity to the next component on the board. You will need to replace the missing resistor as well.

I don't see a C153 on your board, do you?
 

Thread Starter

sull1372

Joined Mar 6, 2019
9
"Cratered" does no sound like a promising description :/
I assumed it was pretty bad since I couldn't identify any contacts at C37, it looked like bare board to me. Whoever attempted this repair was a tad aggressive with the iron.

The display technically works, the back light is on, it's the startup program that is not initiating for the keyboard software.

It appears I have a newer version of the board so mine does nto have the C153 Capacitor. I'll consider that a win.

I will learn how to measure the rail, and research running jumpers. I should be able to trace the continuity of the circuity with the schematic. thank
 

Yaakov

Joined Jan 27, 2019
1,601
"Cratered" does no sound like a promising description :/
I assumed it was pretty bad since I couldn't identify any contacts at C37, it looked like bare board to me. Whoever attempted this repair was a tad aggressive with the iron.

The display technically works, the back light is on, it's the startup program that is not initiating for the keyboard software.

It appears I have a newer version of the board so mine does nto have the C153 Capacitor. I'll consider that a win.

I will learn how to measure the rail, and research running jumpers. I should be able to trace the continuity of the circuity with the schematic. thank
It is possible to repair boards with jumper wires, but check the power supply first. Also, the backlight is probably supplied with 3.3V, so the backlight means little about the rest of the board.
 

Thread Starter

sull1372

Joined Mar 6, 2019
9
Any disruption of communication between the main board and the front panel boards can cause a lock-up. On some early units, component tolerances have resulted in a higher than normal ripple voltage on their 1.8 volt power rail. This ripple negatively impacts communication between the host CPU and the PSoC chips on the the panel boards
 

Thread Starter

sull1372

Joined Mar 6, 2019
9
Sorry didn't mean to post message #14.

Thanks for all of your help. Looking at jumper wires I don't have all of the tools or experience to work with that small sized circuitry. I'm going to have to punt this project to someone who is more knowledgeable. Thanks again
 

Yaakov

Joined Jan 27, 2019
1,601
Sorry didn't mean to post message #14.

Thanks for all of your help. Looking at jumper wires I don't have all of the tools or experience to work with that small sized circuitry. I'm going to have to punt this project to someone who is more knowledgeable. Thanks again
you are certainly welcome. I'm sorry I couldn't help more. Please check back if you manage something.
 

viruzzel

Joined Nov 18, 2019
1
Hi guys.

Im trying to fix the freezing problem too. KORGusa said, if the main board KLM2887 is revision D or lower, need to change couple of capacitors..
im just wondering what revision of the main board of my korg m50? Here the photo of the board with the number.. is it revision C?

Regards
 

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