I reflashed firmware version 1.7.1. After that, the inputs behaved normally.

Unfortunately, for some reason I later lost MADI connectivity, so that RME Connector showed "offline" for the 12mic. After triple-checking my MADI cable setup, MADI connectivity returned. BUT, it had gone back to zero signal at the inputs!

After again checking and re-connecting the MADI cables, connectivity returned, but still no signal at the inputs. So I flashed the firmware again, and the input signals returned.

So I don't know if the problem is solved, but there may be grounds for cautious optimism. If I lose input signal again, I'll post it here and send a problem report to Jeff at Synthax.

-137 is rather unusual. Does this not change with the gain fully turned up? If not, something's not right...

I just double checked. It actually reads -327 dBFS! Which I would assume to be the same thing as dead quiet - no signal.

Yes, we are still handling support for the US. You can send a message to info(at)synthax.com with the serial # and problem report if you would like to send it in for a check up. If the issue is reproducible we can offer options for repairs, etc.

Thanks Jeff.

Should I contact Synthax (assuming they are still doing technical support for the US)?

-137 is rather unusual. Does this not change with the gain fully turned up? If not, something's not right...

No, it did not change. I fear that something is wrong with the 12mic.

I made sure that the gain was up on all the inputs, as I said in my post.

The level meters all showed a very low number, about -137 dBFS.

RME Connect showed no activity on the meters. I can include a screenshot when I get back into the studio later. But it shows nothing at all happening. The gain is at about halfway up for all inputs, and phantom power isn't an issue.

As I said, the same mic and cable plugged into other hardware (without phantom power) resulted in normal sound and meter levels.

I just observed today that there is no signal at the XLR inputs.

That is, if I connect a mic to one of the inputs on the front of the 12mic and adjust the gain of the input to a normal setting, there is no activity on the meter on the front of the 12mic, and no sound comes through my system. There is also no signal shown in the meters in RME Connect or TotalMix. This is the case for all 12 XLR inputs.

If I plug the same mic and cable directly into one of the UFX+ or Octamic XTC inputs, there is a signal as normal.

This setup has worked fine for me for years. I usually use the 12mic to track drums, and it's been a while since I've done that. Just today I found that there was no signal at the 12mic inputs.

I hope I'm not overlooking something obvious. Could this be something that requires service? I can't imagine twelve input preamps going out at once.