I’ve searched this forum and a few others to see if I can get any more detail about either my specific problem, or how a failing/failed MM5823N behaves, but no luck, so here goes:
My MG-1 won’t play notes when the contour tone source is set to keyed. It makes tones on the other two settings, and playing the keys affects the pitch, but when contour tone source is set to keyed, nothing. No polyphony, no notes, nothing. Does this sound like dead MM5823Ns or do I need to poke one of the other ICs? I don’t want to order them from technology transplant if they aren’t needed.
Hey, I’m no expert but I’d check out U13A and Q31. If that wasn’t it, maybe part of U14 is f’d. Fortunately these are all easy parts to find.
Thanks for the response, Benjaminam. Those check out fine with my multimeter. I went through the components in symptom 3 from the service manual found here: http://www.theappreciationpost.com/mg1/MG-1/page-23.jpg
I don’t have problems with symptoms 2 or 4, contour tone source at continuous or contoured. It’s just when keyed. I’m ruling out the wiring in the keyboard harness because when I press a key in either continuous or contoured, it changes key. The Auto Contour Trigger switch seems to work as well. At some point I’ll take it to a more experienced tech, but I was hoping I could sort this out on my own 
Hi. Bumping this thread because I’m having the same problem, and wondering if a solution was ever found. Thanks!
