Hi Ted. There is no front panel jack. I noticed that the phantom power started to get noisy (sounded like 60 cycle hum) about a week before it stopped working. I thought at first the 48vdc failed but dynamic mics do not work either. When it failed, there was no pop, bang, buzz or any other noise, it just stopped passing audio and there is no action on the meter.
On Saturday, I dropped it off with a local tech along with your hand-written schematic