Yamaha Disklavier power supply help - schematic attached

[nickb]

I should also note that the schematic posted is not for the same exact model. The service manual for the piano this came from (a Mark IIXG) does not have a schematic for some reason. I believe that it uses the same or nearly the same power supply as the one I shared (MX1Z) because the layout diagram in both manuals looks to be the same. Further, the next generation Mark III piano service manual has the same layout and schematic as the MX1Z).

What is a little puzzling is that all three of the layouts show IC1 being a 16 pin device (which it is on my board), but the schematics for MX1Z and Mark III show 21 pins? I'm also a bit puzzled about C16 - I can't find on the schematic. It's connected to the bridge rectifier (D4) and pin 15 of IC1. Big filter cap the same size of C13. Looks to be a negative rail.

Any thoughts and guidance are appreciated.

IC1 is numbered with the gaps counted as though there is a pin there.

From the layout i see a difference in the schematic that involves C13. It looks to me as thought the schematic is the the 220V version and the layout is the 110V version.



It is important to realize that a downstream fault could stop the power supply from running. It's not uncommon for the primary side circuit to detect over current and shut it down. With a scope ( and suitable isolation) you'd see a few cycles where IC1 tries to start up. On the other hand, if it turns out that IC1 is bad I would not be too happy about forking out $50 for a chip that is hard to get. If it blow that your are back to square one and out of pocket. All not helped by not having a datasheet. I would seriously consider replacing the whole power supply with a linear one, even is it mean housing part of it external to the keyboard.