Assuming plug-in-power is turned on, you should be able to measure a voltage of around 1.5V to 5V (typically around 3V) between the sleeve (ground) and tip or ring connections of the TRS mic input jack.
It shouldn't matter if the tip and ring connections are shorted, which is what a mono TS mini-jack plug will do when inserted in a stereo input jack. You should see the same voltage.