I have one. Will see if I can find time to extract it from my MIDI pile and open her up this weekend.

Kahenraz wrote on 2022-02-04, 14:58:

I removed the battery on mine some time ago but lost the photo that was to remind me of the polarity. Would someone with a Yamaha MU50 that still has its coin cell share a photo of the PCB?

Thank you.

Couldn't you determine the polarity by measuring resistance between a known ground point elsewhere on the board (like the DC power input jack) and both battery terminals ?

I've read that identifying the polarity in this way is not always reliable.

Kahenraz wrote on 2022-02-05, 06:37:

I've read that identifying the polarity in this way is not always reliable.

Well, I'm definitely not an authority on this and I can imagine potential situations (i.e. if there is a current limiting resistor somewhere) where measured results could be ambiguous, I can't really imagine a scenario where a reading of continuity between one of the battery terminals and a known ground point could lead to any other conclusion than one where it is unambiguously safe to consider that the aforementioned battery terminal is ground .

That being said, I may be in error and would love to be corrected if I am .

The battery in these kind of devices always has one singular purpose and ground is always connecting to the negative terminal while positive goes to a diode or some battery management chip and then to a memory chip. You'll see other arrangements in analog applications where a negative voltage may be necessary but those cases usually are not going to use a soldered battery like so.

Here you go:

Irritatingly illogical thing to open. Battery has inscribed side up.

Perfect. Thank you. 😀