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What I found is more interesting than a short.

First of all, the power supply uses mag amps to regulate each output.? That's not very common!

Each output is floating with respect to the others in the supply. When the supply is plugged into the backplane the four outputs have their commons tied together and to chassis ground.? So my first thought was that there was a short inside the switcher transformer that led to high currents when the outputs were tied together. Measurements ruled that out.

Measuring the voltages of the outputs led me to the problem.? The +12 was at +23 volts.? So the +12 volt regulator has a fault.

The key finding is that there is a supervisory circuit in the supply which guards against such failures by crowbarring the supply.? But, its design only works when the individual supply commons are tied together.? With the +12 supply left floating the overvoltage protection circuit cannot sense that fault and the supply runs.? Tie the commons together and the overvoltage protection circuit keeps the supply from running, as intended.

I got the CLIP very quickly online from Artek Media and will track down the component fault when I get a little more bench time.

If you are curious about the mag amp angle, the control chips they use are UC3838 and the datasheets are easy to find on the web.? If the fault in mine is that chip, it is available.

Peter