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Korg M1 no power / not turning on

 
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Coilbacklew



Joined: 06 Mar 2020
Posts: 2

PostPosted: Fri Mar 06, 2020 7:56 am    Post subject: Korg M1 no power / not turning on Reply with quote

I recently inherited a Korg M1. It looks to be in perfect shape, but will not turn on. I opened it up and checked the fuse and it seems to be fine. I dont see any bad caps (just the usual tons of glue), no cracked resistors etc. I hate to scrap it since it seems to be in really nice shape otherwise but also dont want to sink a lot of money into it to get it working. I'm located in DFW, TX if anyone is curious.

Anyway, I'm assuming it pretty much would have to be the power supply board (obviously a component on it) since nothing at all lights up or even remotely tries to turn on when the switch is turned on. Any ideas on where to start looking past what I have looked it?
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voip
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Joined: 27 Nov 2014
Posts: 3312

PostPosted: Fri Mar 06, 2020 8:47 am    Post subject: Reply with quote

The power supply is the most likely culprit. It's worth checking that power actually gets to the PSU input, as the power switch may not be working (repeated operation of the switch might clean off contact oxidation). If mains gets to the PSU, measuring the PSU outputs might reveal if only one supply is down, or all of them.

.
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the_crimson_thunder
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Joined: 18 Nov 2014
Posts: 91
Location: Germany

PostPosted: Fri Mar 06, 2020 11:52 am    Post subject: Korg M1 no power / not turning on Reply with quote

If there's no power at all it's most likely that the electrolytic capacitor C11 is defective - but bear in mind that even it's defective it could hold a high voltage and zzapp you if you aren't carefull! I highly recomment to replace all of the electrolytic capacitors - they don't cost a fortune. I also recommend to take capacitors with a higher voltage - and take care to buy 105ºC types! Also take care for the polarity while replacing!
Here's a pic how the power supply is looking - the 'green' values are those I recommend to use (prolongs life):
https://www.img1.de/?img=PSU110Vnewcaps33197.jpg
After replacing the capacitors you have to connect the psu to the mainboard - otherwise it wouldn't work due needing a certain load to operate properly! With VR1 you can adjust the output voltage - please adjust the 5 volt output as close to 5 volt as you can get it - the other voltages should be within their specs then.
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Coilbacklew



Joined: 06 Mar 2020
Posts: 2

PostPosted: Fri Mar 06, 2020 1:19 pm    Post subject: Re: Korg M1 no power / not turning on Reply with quote

the_crimson_thunder wrote:
If there's no power at all it's most likely that the electrolytic capacitor C11 is defective - but bear in mind that even it's defective it could hold a high voltage and zzapp you if you aren't carefull! I highly recomment to replace all of the electrolytic capacitors - they don't cost a fortune. I also recommend to take capacitors with a higher voltage - and take care to buy 105ºC types! Also take care for the polarity while replacing!
Here's a pic how the power supply is looking - the 'green' values are those I recommend to use (prolongs life):
https://www.img1.de/?img=PSU110Vnewcaps33197.jpg
After replacing the capacitors you have to connect the psu to the mainboard - otherwise it wouldn't work due needing a certain load to operate properly! With VR1 you can adjust the output voltage - please adjust the 5 volt output as close to 5 volt as you can get it - the other voltages should be within their specs then.



I had a feeling that was probably the issue though they all look ok, but I know that doesnt always mean anything. I guess I can start with the caps. Any tips for getting rid of all the glue goop all over them without damaging everything around them? They managed to plop it all over the nearby resistors and such
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the_crimson_thunder
Junior Member


Joined: 18 Nov 2014
Posts: 91
Location: Germany

PostPosted: Fri Mar 06, 2020 1:59 pm    Post subject: Korg M1 no power / not turning on Reply with quote

My experience with that kind of glue: once you have desoldered the capacitor's pins (best is to use a vacuum sucker/desoldering iron, maybe in combination with some desoldering braid) you can wiggle & jiggle the capacitors loose whilst pulling them at the same time - no big deal.

BTW: where you're located the mains power is 110/115 volts, isn't it?

If so the voltage I recommended to use for cap C11 is ok...
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voip
Platinum Member


Joined: 27 Nov 2014
Posts: 3312

PostPosted: Fri Mar 06, 2020 2:15 pm    Post subject: Reply with quote

Just a thought. C11, rated at 100 or 250V DC working voltage, is fine for 110V AC mains, but not for 230/240V AC.

The 230/240V AC supplies have C11 and C12 in series.

Korg didn't put much gunk on their boards. Chances are, it's capacitor contents exuded over the board.

PS Crimson Thunder got there first!
.
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Jonathon



Joined: 08 Apr 2021
Posts: 7
Location: West Sussex England

PostPosted: Sun Apr 11, 2021 1:10 am    Post subject: TRY THIS Reply with quote

search my recent post to samish problem
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