Korg M1 turns on, no sound, screen blank

After about 2 years not using it, I dusted it off, turned it on and there were no sounds (a click in the headphones when you power up or turn off on full volume), and even though something showed up, the screen was essentially blank as in the photo below.

I opened it up and changed the battery (multimeter read it as 1.3V) and also noticed what looks like a leakage as in the photos below:

I assume this is probably the reason the synth is not working?
I guess the leaking capacitors need replacing, along with the resistors with leakage engulfing them?
Anyone recommend which type I should buy?


That is definitely worth looking into.

It’s typical for a manufacturer to glue components to the board. That’s the brown paste you typically see around components. However that looks like something chemical may have been eating into it. Especially near the transformer.

I have had bad electrolytic capacitors that didn’t show signs of leaking. Over time they drifted in value.

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I took the caps off a few resistors and one diode.
The caps did not look too bad. I will replace anyway. The resistors looked like they had seen better days and the diode and resistor that sat next to it looked like they leaked.
The glue was a PITA. I used some GooGone to help loosen the glue up.
The two green components (what are they called?) I took out to clean the glue off, and will put back.

I cannot work out what replacement diode I would need to purchase.
D4 on a KLM 1267 PSU board.
Do you know?
The colours are:


Okay, I’ve tracked down a schematic for the M1.

It’s hard to make out what’s written on the power supply section for D4. It appears to be 1SS86 which is a high frequency diode.

The green things are coils.

Looking at the schematic, I think we’ve got a switch-mode power supply. Your diodes, coils, and resistors are probably okay. Due to age, those caps are suspect.

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When I touched the wire part of the diode, it cracked due to corrosion, it looks like.
I took out the resistor next to it too.
Also, I took out the resistors which were caked in glue.
I have a question. Using a colour guide, I figured out which resistors I need, but I am not sure about the voltage.
For example, I need a 220 ohm with a 5% tolerance, but there are 5V, 1V, 10V, etc. options. Which option do I go for?

Okay, I’m confused. I’ve never seen resistors rated by voltage. Resistance, tolerance, and wattage. You want to get the resistance correct within the tolerance, so as long as you’ve read the bands right you’re okay. Wattage is an indication of the maximum current the resistor can withstand before it burns up. (P=IE) There is no drawback to having a bigger resistor other than the physical size.

I’m seeing a mix of resistors in the power supply schematic from 1/4W to 2W. The only 220 ohm resistor I see is R22, which is a 1/2W. It’s across the +5V supply output.

Yes. If the part is cracked, it’s bad. good catch.

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Yes, I made an error, it is wattage.

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The stuff you see is not cap leakage, it’s glue used to make the boards vibration proof. However it does become corrosive and eats components as you see. The service manual has the component values and types in the schematic for the power supply. If you have broken diodes and resistors you need to replace them. With the M1 I worked on it had exactly this problem. All was fine after I serviced the low voltage side of the power supply.


One question. Does the voltage rate matter with the capacitors?
Say it is 2200uF and the voltage is 10v and I used something over 10v, say 25v, or under 10v, would it matter?

Capacitors are one of the simplest components, but buying a replacement can seem give you a headache with all of the specifications out there.

The voltage rating of a capacitor is the maximum voltage that it can sustain. A replacement capacitor should be the same voltage rating or higher. Put 25v across a 10v capacitor and it will likely pop like a firecracker. Put 10v across a 25v capacitor and everything will work normally.

Some capacitors are polarized. There will be a pin marked as negative (-) or rarely as positive (+). The replacement should be installed in the same direction.

You’ll also see mention of radial or axial. Radial means that the leads are on the same end, while axial means that the leads are on opposite ends. Either will work, but using the wrong one can cause stress on the leads leading to premature failure of the cap.

The last consideration is the physical size. Sounds crazy at first, but even though capacitors have become smaller than they were 30 years ago, it’s still possible to get one that can cause difficulty getting the cabinet closed…

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I think that the previous poster mixed up his sentence. With replacing capacitors keep the capacitance the same ie uF value as the old one. So if the old one is 1000uF 10V then replace with 1000uF 10,16 or 25V. Higher voltage is recommended even but do NOT go under the original voltage rating or it will go pop! It will also go pop if you put it in backwards so always take a photo before removing the old capacitors keeping mind of positive and negative sides of electrolytics.


Is it the 1SS84 rather than 86?

The colours match in the specs for the 84.

Looking at equivalents for the 84, I found the 1N4148
The specs are not the same. The forward voltage is 0.8 for the original and 1V for the 1N4148.
The forward current and reverse current (has three readings?) are not the same, either.
Would that matter?

That might be. My copy of the schematic is poor, and that last digit is not very clear.

I’d say try it and see if it works. Nothing critical here - just an oscillator driving a transformer. I think it it’s close enough to get the power supply started, your keyboard will come up.

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Just thought I would update this.
I got it ruining again. So, it was an issue with the power board.
Thanks for the assistance.

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