Hi, 
I have UNO2 1.4 but when I send data from my PC to UNO using control center, it looks like MIDI Thru/Merge on the FCB1010 is turned on.  The merge function is not enabled in control center. Here I send a control change with control center and as you can see, it is echoed back but the MIDI Thru box is unchecked.

Correct - you can read more about it on p.13 of the manual. UnO2 firmware implements MIDI THRU, the "send" function in the MIDI monitor screen is intended to test the behavior of the controlled gear by sending MIDI to that gear, not to the FCB1010.

So it doesn't pass through incoming MIDI messages if not using the MIDI monitor?  I don't want messages that are sent to the FCB1010 to go back out. Just messages originating with the FCB1010 itself.  I read that section in the manual and it was confusing to me. According to what I read, it looks like it always implements MIDI Thru except for some SysEX messages. 

Sure, MIDI THRU is always active. It only makes sense to send MIDI messages to the FCB1010 if you want to merge and forward them to the connected gear. Except for the editor, which sends messages to communicate with the FCB1010 - those are not forwarded, and then the specific case of remotely controlling the FCB1010 - those commands are also not forwarded. 

OK, well that is too bad as I wanted to not have to disconnect and re-connect cables when programming using the computer.  Attached shows my setup.  I merge MIDI with my FCB1010 and my 2 synths using a merge box.  I can tap off another output to send to the computer when I'm using FCB control center. I can then send MIDI for programming from control center directly. (or another app if I want to remotely control the FCB1010). Unfortunately, most MIDI messages sent to the FCB1010 from a computer application will ultimately go to my synths as well  which I don't want. I guess I will need to filter out those messages by putting them on another MIDI channel and setting the remote control channel accordingly. My desire was to turn off midi thru and never have to connect and disconnect any cable in my setup.

It wouldn't be too hard to put a switch inline in the MIDI cable to effectively turn it off.  Not ideal, but a little better than having to disconnect and reconnect.  DIY'ing a cable makes it easier to connect the switch in the right place, but a multimeter can find the right wire on any cable, even with a formed plug housing.

Just put the switch in line with pin 5 of the connector.  Just about any kind of switch will do, but keep in mind that any parts that stick out will tend to get caught on things, so a slide switch would be better than a toggle switch.

Yeah, I can still make it work by making the REMOTE control channel on a channel that none of my devices listen to.

On Thu, Jan 12, 2023 at 09:30 PM, Jack Fenton wrote:

making the REMOTE control channel on a channel that none of my devices listen to

That is exactly the reason why MIDI channels exist.

But I still don't see which "unwanted" messages could be passing through the FCB1010 MIDI THRU : 
- as mentioned before remote control messages are not forwarded (so there's no need to use a channel that none of the devices listens to - but it's good practice to use a dedicated channel for each device) 
- patchdump and other editor communication messages are not forwarded
- other MIDI messages sent by the computer are .... what exactly? It could be MIDI sent from software apps to control your synths, that's when the MIDI THRU of the FCB1010 is needed