Since I acquired my first DB50XG to play with MIDI on my Amiga500, I have always asked myself why they(Yamaha) did put a useless MIDI OUT pin on the connector of their daughter-boards.

Following the tracks on the board I can see that they are not cut, they are connected and seem to have some functionality that, until now, It had always gone unnoticed by me.

Just a week ago I have found on Ebay a very cheap Yamaha MU10, 50€+shipping from France to Spain. I couldn't pass up an opportunity like that....

Basically it is like a DB60XG(XR385) on a box(it can also work on 6 AA bateries...) with some additional volume controls. It is one of the few modules that have QS300 voices included... Some web pages say that it has lower sound fidelity than a DB50XG, but I didn't noticed the difference. It works really well.

It has a serial To-Host connector and MIDI IN/OUT connectors, so I, being a connexion freak, immediately downloaded the manual from the Yamaha site, and searched directly for how the MIDI OUT is used: Not used.... it is only a direct MIDI OUT for the computer in the case the To-Host cable is used, not my intention.

Ok, again a locked door.... Then I searched for a service manual. Yamaha has internal service manuals that they share with electronic workshops to allow the reparation of their devices. Sometimes these manuals surface, and then parts used, schematics or the secret laboratory-procedures can be read. This time the manual was in the hands of Scribd, a damned website that charges money for downloading documents that should be free. Ok, I can't download it but at least they let me read it: https://es.scribd.com/document/734849722/yamaha-mu10-sm.

On pages 17 and 18 of the Service Manual they describe a procedure to test some of the functions of the module:

Observe that Sysex sequence: "F0 43 10 18 5A 00 f7". If you send that Sysex to the MU10 it puts itself in "Test Mode" and begins to output data from its MIDI OUT port. Exciting, isn't it?

If you search "F0 43 10 18 5A 00 f7" on Google you will find that the sequence is also used on a lot of other modules or keyboards to enter their Test Mode, but once done, with different procedures. So, then I asked myself....: what if it also works on the daughter-boards..... and effectively it works. But every module has its tests numbered differently, it is up to you to find what do each one....

This is a short test done with MidiOx, first with a XR385 and then with a DB50XG.