Thanks mjrippe for the schematics.
I have been using an MX6/2 for quite a few years now and absolutely love it. I have recently bought an MX6/3 but it has a few issues with noise and one malfunctioning EQ card.
My plan was to swap the cards from the 6/2 to help diagnose where the noise issues are coming from but when I started taking them out I saw that they are different in the two different mixers. The 6/3 has the cards shown in the manual (in particular pcb GS317/2 for the output card and GS318 for the mixer card). The 6/2 however has slightly different circuit boards and components for those two modules ( pcb GS177/7 for the output card and GS178 for the mixer card). I would guess that 177 and 178 are earlier versions and this would fit as a numbering system with the input amps being on pcb GS173/5
I'm fairly certain that they are interchangeable as all the buttons and connectors are in the same place and they have the same ins and outs (though slightly different layout). I've also looked on google and seen versions of the 6/2 with both sets of cards. In the end I imagine it just comes down to the pins on the connector being the same.
So am I safe swapping the cards over?