Bob,
If you check the voltage at the 12V DC mini-circuit breaker, when the converter and breaker are working properly, both sides of the breaker should read 13.2-13.6V DC to ground. The side with the copper strip connecting the breakers is the battery side. The other side goes to the converter. If the converter side is reading 13.2-13.6, but the battery side is reading 12V or less, the breaker has tripped. If you want to check for converter output, turn the battery cutoff switch to OFF and take a reading at the mini-breaker. If you don't get any voltage on either side, there's no converter output.
If you recently worked on the batteries, you might have blown the on-board fuses on the converter. As mentioned, it's usually behind the rear wall of pass through basement storage. Also check to make sure it's plugged in. And before you take the wall down, check the main circuit breaker panel inside the coach to make sure the breaker for the power converter hasn't tripped.
One other thing. If other 120V AC devices aren't all working, you may have lost one leg of your 50 amp power.