Hello! I have a Korg M1 that I’m trying to restore. Unfortunately I’m no professional service tech but I love to learn and I’m good with a multimeter and soldering iron. Over the past few months I have gotten everything on my M1 working correctly except the right output and headphone jack. The issue is that my M1’s right line out outputs sound at roughly half the volume of the operational left output jack. Also, the right line out has a very noticeable hum. What’s more is that the M1’s headphone output has the exact same low volume and hum on the right side as well.
I’ve tried reading the service manual to perhaps trace back where an issue might originate from however I’m rather green when it comes to understanding circuit board diagrams. I can trace/follow paths and identify IC’s, resistors, capacitors, etc. with relative ease but I don’t understand much past that.
If anyone can offer some advise on this matter, I would be eternally grateful. Thanks to all who read this and I wish everyone well during this time.
For anyone experiencing this same issue, I’ve found and fixed the problem. My overall issue was as above, low volume, noise and a ground hum would come from the right channel on both the headphone output and the main R mono output. Also, when I would increase the volume slider anywhere past 50% and hit a note, major crackling in the right channel would become an issue (like the sound was trying its best to come through/normalize but couldn’t).
What fixed my problem was replacing IC2 on the KLM-1262 board. The chips model number is M5216L (cost about $10 on eBay for a replacement), and is the OP amp in charge of amplifying the original L/R mono signal to a signal loud enough to be sent to the stereo headphone output. This op amp has two inputs, one for the original L channel audio, the other for the original R channel. I’m no tech but my guess is that the 2nd input (R channel) of this op amp failed and caused some sort of short, leading to both the loud ground hum/volume issues in the headphones as well as the main R mono out since the signal path originates from the same internal path.
It was a relatively easy fix one I poked around. The only major pain with this fix is that you have to quite literally take the entire keyboard apart to access the underside of the board for removal and replacement of the IC.
Hope this helps someone in the future.
Thanks! I have the exact same issue here: even less than half volume coming from the right output, but also hum/noise, etc.
As soon as I start restoring the M1, I’ll know what to check out!