KORG M1 - No sound / Low battery indication. SOLVED!

[Yekuku]

Hi, I have the inconvenience of battery low (internal). According to what I read, I initially changed the C23 for a new one, and everything remained the same. Then I changed the rest (c11,19,18,21 ... etc) and it keeps telling me the same error. Any idea what the fault may be? I inherited the keyboard. my father used it to work, and when he died it was me. It was a while without being used and when I turned it on it said that error. I had the programs but did not emit sound. I changed the battery and it was reset and I could not remove that low battery message.

Hi and welcome on the board.
Please confirm that you are getting 12V, -12V and 5V from the power supply.

[HeMagliano]

Hi, I have the inconvenience of battery low (internal). According to what I read, I initially changed the C23 for a new one, and everything remained the same. Then I changed the rest (c11,19,18,21 ... etc) and it keeps telling me the same error. Any idea what the fault may be? I inherited the keyboard. my father used it to work, and when he died it was me. It was a while without being used and when I turned it on it said that error. I had the programs but did not emit sound. I changed the battery and it was reset and I could not remove that low battery message.

Hi and welcome on the board.
Please confirm that you are getting 12V, -12V and 5V from the power supply.

I'm not getting the right voltages. Instead of -12 have 22 And instead of 5 I get 10. The keybord is getting check by a service now But i think i can give him an idea with your help. Thanks!

[Yekuku]

Obviously the problem is located in the power supply.
The fact that you are getting 10Volts instead of 5V is bad news, digital components dont like overvoltage.
Good luck, let us know how it goes.

[HeMagliano]

Obviously the problem is located in the power supply.
The fact that you are getting 10Volts instead of 5V is bad news, digital components dont like overvoltage.
Good luck, let us know how it goes.

The first was an oxidized welding of a coil (the green things in the power supply). and also an R80 resistor in the DAC. When it is resolved I tell you.

[Leeroy001]

Hello, First time poster here. Hello all

I have a beat up old Korg M1R which I have been working on, trying to bring back to life. Ive got it to the point where it mostly works. After replacing the battery, loading the default patches I noticed intermittent sound cutting in and out, no pattern to it, all audio, via outputs or headphones, on the demo songs etc. On the weekend I replaced a few of the tactile switches, and noticed the sound drop out slowly getting worse on powerup, ending up after maybe 10 mins having virtually no sound. This afternoon I checked the power supply, have good 5V, -12v, had +12v, then it went away, came back, then went altogether. At this point I have close enough to 0V where should be +12, but have good -12v and good +5V. Capacitors have passed the visual test( no swelling or leakage that I can see). Just wondering if anyone had any advice or tips on measurement points for the loss of the +12v source? I live in a remote location in Australia so components are not just off the shelf for me. I can however order components through a local battery shop. Thanks in advance, this post has some great info so hopefully it gets seen (Oh BTW the board I have is the KLM 1269) thanks again

[Yekuku]

Hi ,
The problem could be the psu but there is a chance that a component on the mainboard is failing short dragging the positive analog power line down.
My bet is that the filtering cap at the end of the psu 12v line needs replacing.
Sorry i am on vacation and i dont have access to schematics

[Leeroy001]

Hi ,
The problem could be the psu but there is a chance that a component on the mainboard is failing short dragging the positive analog power line down.
My bet is that the filtering cap at the end of the psu 12v line needs replacing.
Sorry i am on vacation and i dont have access to schematics

Thank you Yekuku for the quick reply. I am measuring voltages at the -12V Gnd Gnd +12v connector on the PSU with the cable disconnected. Interestingly I left if for a few hours, measured again and got 9v at the 12v pin, slowly dropping. Will certainly start with the 2 capacitors, C18 and C19 according to Circuit diagram They look fine but you never know internally. I will take them out and order a couple of replacements. cheers

[stanchfi]

Firstly let me say I have a limited understanding of electronics. I kind of understand how each component works, but how they interact is beyond me. If I can find a bad part I can replace it, but that is about it

I picked up 2 Korg M1s at an auction, and luckily one of them work (except the buttons needed replacing)
The other one would not power on at all. I swapped power supplies and it worked fine, so decided the issue is the KLM 1267 power supply board.

Having in the "bad" power board plugged in, but not connected to the keyboard, I was getting voltage at 5- and 5+, and was getting voltage at -12, but was getting low or no voltage at +12.

I figured the likely problem was the capacitors, so I replaced C18, C19, C20, C21, C22 and C23 and there was no change in the voltages.

I started testing for resistance around both boards to see if I could determine where a difference was between the two.

I finally checked both sides of the D6 diode.

On the good board, I got .3 one direction, and .5 when I reversed the positive and negative leads.
On the bad board, resistance would almost drop to zero, then start rising again getting to 50-60 (on the 200k ohms setting)

I just tried to double check things, with power to the bad board, but I am not getting any output voltage, 5 or 12.

Any ideas where the issues may lie, or what I can test to determine what components might be bad?

thanks
-James

[Yekuku]

Hi and welcome to VSE.
the psu is not generating -5V, how come you are measuring -5V?
With no load on the PSU, what voltages are you getting exactly?
The diode could be a suspect , remove it from the the pcb in order to test it properly.
Check L3 for continuity, and share a pic of the PSU.

[stanchfi]

Firstly, thank you for keeping this thread alive for over 11 years!
This was the only resource I could find on these power boards.

Secondly, I misspoke in my previous post, I meant +5 volts.

Currently, I am not getting any voltage at the output pins/connector.
Before I was getting 5 to 6 volts at the +5, -12 to -15 at the -12, and 2 to 3 volts at the +12, with no load.

I believe what completely killed the board, was testing for resistance.. which seems really strange for me.

Checking the board completely unplugged (though recently plugged in, so there is probably a charge in the caps)
When I check for continuity for L3....with my multi-meter set to 200K ohms, resistance climbs to about 50 to 70, resets to zero , then starts climbing again

L4 shows zero resistance when checking it the same way

thanks

[Yekuku]

L3 is a coil and it should have very low (aprox 0 Ohm) resistance. It looks open, remove it from the pcb and test it.

[stanchfi]

I removed L3 and tested it, and it has zero resistance, so I'm guessing it is not the issue

[Yekuku]

Testing coil L3 in circuit and off circuit should have the same results, that is strange.
Probably the fuse was blown, that is why the psu is not generating any voltage now.
Did you check/replace the fuse ?
next thing is to measure voltage across D6 with the psu powered on.

[stanchfi]

I put L3 back in. With the PS on I'm not getting any voltage across D6.
I also do not appear to be getting any voltage on the output side of the transformer.
The fuse tests fine.

How can I check the D1 rectifier?
Or is there something better to test next?

[Yekuku]

I assume that the psu is not generating any voltage.
Since the fuse is ok, you should test the switch , with the psu offline test for continuity on the power switch pins.
Working on the primary side of the psu is dangerous, it can be lethal, so you need to be extra cautious.
Assuming that you are on 120V, the bridge rectifier takes AC and spits out DC.
With the psu powered on, take readings touching the pins of the rectifier that have the sine wave symbol.
You should get near 120V AC.
On the other pins you should get aprox 180V DC ( I am guessing here)
The brigde rectifier is a suspect in a case of a dead psu, so you can go ahead and replace it.
Another suspect is C11 , Q1 and Q2.
Check the light bulb trick for testing switching mode power supplies.
Be careful when working with live high voltage.