Vintage Synth Explorer Forums

Took a chance today and bought a broken Korg Kontrol49 for $25.
The thing won't power up, neither USB- nor wall wart-powered.

I've opened it and located a 470µF/16V electrolytic near the DC input that's blown. Other than that no parts appear damaged on visual inspection.

The guy told me he had used another supply than the 9V DC one that came with the controller by mistake. He didn't remember which type so he may have plugged in anything; AC, wrong polarity, too high/too low voltage... anything.

It's a long shot without schematics or a service manual, but since I'm going to buy a replacement for the 470µF/16V cap tomorrow, is there anything else I should definitely check out/replace right away along with the cap?

BTW. The Kontrol49 uses the same power supply as the MS2000 and many other Korg machines, so I figure the internal power sections may be similar, if anyone has knowledge of those.

just a guess, but i'll bet ther;s SOME kind of fuse in the power input area: maybe not the standard glass tube. could be a plastic block or look like a round,flat ceramic cap.

prinsen wrote:Took a chance today and bought a broken Korg Kontrol49 for $25.
The thing won't power up, neither USB- nor wall wart-powered.

I've opened it and located a 470µF/16V electrolytic near the DC input that's blown. Other than that no parts appear damaged on visual inspection.

The guy told me he had used another supply than the 9V DC one that came with the controller by mistake. He didn't remember which type so he may have plugged in anything; AC, wrong polarity, too high/too low voltage... anything.

It's a long shot without schematics or a service manual, but since I'm going to buy a replacement for the 470µF/16V cap tomorrow, is there anything else I should definitely check out/replace right away along with the cap?

BTW. The Kontrol49 uses the same power supply as the MS2000 and many other Korg machines, so I figure the internal power sections may be similar, if anyone has knowledge of those.

Not sure but I'll make a substantial bet that if you replace the cap it still won't work. Sounds like the main resevoir cap and it didn't take kindly to being overvoltaged and/or reverse polaritied. I'd expect the next stage in to be a voltage regulator - if you are very lucky it's either this reg gone or just possibly some form of protection device before it. I'd like to think any engineer would design a piece of kit to sustain such abuse without major damage but it always amazes me just how poor some designs are. My gut feeling is that you've probably gotten away with it.

Thanks Rhino and Hideaway.

I've tried analyzing the circuit. Here's what happens near the DC input:

(There's one component I don't recognize, called "L6". I'm guessing it's a coil, but I don't really know anything about coils. Didn't get to those in my electronics training yet . It's a small black block, about 5mm X 5mm X 4mm (l w h), with four terminals and the number "84" printed on top of it. Two terminals are connected to the + side, and two terminals are connected to ground)

9V DC + has direct connnection to:

• C10, C77, and C80, small capacitors, each connected to ground on the other side
• L6, connections mentioned above
• D3 (has 3142 printed on top), cathode goes to the blown 470µF cap and a BA05 based regulator circuit.

How do you best check the state of regulator circuit? There's no visible signs of damage from possible over heating.

I can't find the Kontrol49 service manual anywhere. But I found a schematic for the MS2000 power block which look similar, not identical.

Here's a snap shot of the MS2000, NOT the Kontrol49:



(If I'm doing something I shouldn't, let me know, and I'll remove this imediately)

Excuse me for my manic triple posting.

HideawayStudio wrote:My gut feeling is that you've probably gotten away with it.

Huh? I'm not sure I speak gut'ish.

Do you mean the Kontrol49 is gone or that I may have gotten away with taking a chance on a broken piece of equipment?

prinsen wrote:Excuse me for my manic triple posting.

HideawayStudio wrote:My gut feeling is that you've probably gotten away with it.

Huh? I'm not sure I speak gut'ish.

Do you mean the Kontrol49 is gone or that I may have gotten away with taking a chance on a broken piece of equipment?

What I mean is I doubt it's badly damaged. It will be a failed regulator, fuse, cap, diode etc... all inexpensive and fairly easy to diagnose with some basic electronics knowledge.

prinsen wrote:Thanks Rhino and Hideaway.

I've tried analyzing the circuit. Here's what happens near the DC input:

(There's one component I don't recognize, called "L6". I'm guessing it's a coil, but I don't really know anything about coils. Didn't get to those in my electronics training yet . It's a small black block, about 5mm X 5mm X 4mm (l w h), with four terminals and the number "84" printed on top of it. Two terminals are connected to the + side, and two terminals are connected to ground)

9V DC + has direct connnection to:

• C10, C77, and C80, small capacitors, each connected to ground on the other side
• L6, connections mentioned above
• D3 (has 3142 printed on top), cathode goes to the blown 470µF cap and a BA05 based regulator circuit.

How do you best check the state of regulator circuit? There's no visible signs of damage from possible over heating.

L6 is almost certainly a common mode choke. It is there to reject noise on the power supply rails.

If you have a multimeter you need to connect the negative lead up to ground on the pcb and trace the input voltage through all of the PSU input stages. Is there 9 volts or so on the input pin of the regulator? Is there 5 volts on its output? If there isn't then the damage is going to be very limited and should be very repairable.

Was the blown cap a tantalum? A tantalum will nearly always be the first thing to blow when you hit the circuit with the wrong voltage. It's probably acting like a low resistance across the power rail now.

You might want to check around the board for any more blown tantalums.

HideawayStudio wrote:If you have a multimeter you need to connect the negative lead up to ground on the pcb and trace the input voltage through all of the PSU input stages. Is there 9 volts or so on the input pin of the regulator? Is there 5 volts on its output? If there isn't then the damage is going to be very limited and should be very repairable.

Thanks again!

I've got both multimeter and basic knowledge of electronics, but I'm still very much learning.

Checked the voltage - twice using two seperate PSU's.
- on input it's about 5,38V - I assume this is an indicator that some component(s) are faulty. Wouldn't I see higher voltages before the BA05 5V regulator?
- on cathode of the "3142" diode it's 5,04V (normal diode voltage drop I believe), and thus the same at the voltage regulator input
- on the regulator output it's 5V straight

Also, I just ordered the PDF service manual from Paintingwithsound in New Zealand. Hope that'll clear some things up.

cornutt wrote:Was the blown cap a tantalum? A tantalum will nearly always be the first thing to blow when you hit the circuit with the wrong voltage. It's probably acting like a low resistance across the power rail now.

You might want to check around the board for any more blown tantalums.

Thanks. The blown cap was an electrolytic. Most of the other caps are tiny SMD's, so it's hard for me to tell if they're tantalums or not.

The SMDs are probably ceramics. Those hardly ever fail.

OK, I should have done this before... but today I took out the pcb that has all the controllers mounted onto it and found the remains of a liquid spill near the rightmost slider.

After cleaning up the mess I discovered that one pin of one of the ic's affected by the spill had come lose. After soldering the pin back in place I managed to power up the Kontrol49 using the USB bus power of my Asus EEE subnotebook. The Kontrol49 is fine. Only two issues remain:

1. During the troubleshooting process I got a phone call and forgot that I had left the power supply plugged in. The psu got killed during the phone call, possibly from current over drain from the (at this point) faulty Kontrol49. Without the psu I can't test the dc input at the moment.

2. My Asus EEE will power up the Kontrol49 just fine, but my Macbook (white early 2008 version) won't. The Kontrol49 says "low power" when I hook it up to the Macbbok. My guess is that this is due to the Macbook not being spec'd to deliver the power that the Kontrol49 needs. Anyone succesfully powering a Kontrol49 from a Macbook similar to mine?