Preamp Power Supply Trouble Shooting
If the output voltage drops before full output current is reached there is a failed slave module. We have seen
this in a subtle was since some supplies can almost power the load with a single failed slave module.
We have seen bad connections on the board inside the MegaPAC that the module plugs into.
When there is no output the master module is bad.
If the fuse on the board blows there will be no output voltage or current on that channel.
The supply will however read the voltage from the backup supply if it is ON.
If a fuse blows on the wiring fanout there will be no current for either supply to that path.
We have seen loose wires that show up as slowly changing current levels as the connections heat up.
Some of the current readback circuits have bad OPAMPs (INA117KU) that show up as negative
currents on the power supply that is turned OFF. This is a common-mode problem where the output current changes
as the output voltage changes even when there is no current flowing. Replacement of the OPAMP is necessary.