Hobart 6T28-600CL Operation And Maintenance Manual page 57

OM-2244 / Operation and Maintenance Manual
DCS-600/ Series 500082 / Solid State Transformer-Rectifiers
Two thermostat switches mount to the top of the heat sink assembly. Refer to Chapter 4-3, Figure 7.
The switch on the left side controls the fan. The switch on the right side shuts down the GPU when an
overload occurs.
The fan thermostat is normally open. If this switch fails in the open position, the fan will never turn on
and the unit will eventually shut off with an overload indication. If the fan thermostat fails in the closed
position, the fan will run continuously, even when the unit is cold. This switch turns on when the
temperature reaches 100° ± 8° F and turns off when the temperature falls back down to 80° ± 5° F.
The overload thermostat is normally closed. If this switch fails in the open position, the GPU will not
produce any output voltage. If this switch fails in the closed position, the GPU will not shut down if the
heat sink gets too hot. This switch opens when the temperature reaches 190° ± 5° F and closes when
the temperature falls back down to 172° ± 8° F.
Both of these switches can be tested using an ohmmeter and a heat gun. To replace a thermostat,
unplug the wires and then remove the two screws that hold it. Reconnect the wires to the new
thermostat.
e) Fly-back Diode
The fly-back diode, CR7, is located on the left side of the heat sink assembly near the base. Failure is
not common, but if fails in a shorted condition, it can cause high input current. Refer to Chapter 2-1
for troubleshooting information.
Chapter 4-3, Figure 7 gives the part number for the diode.
(1) Buff the heat sink in the area where the diode attaches to remove any oxidation.
(2) Smear a thin film of Burndy Penetrox "A" (or similar oxide-inhibiting electrical joint compound) in
the area where the diode attaches to the heat sink.
(3) When replacing the diode, torque the nut to 4.2 to 5.2 ft-lb. (5.7 to 7.05 N-m).
December 15, 2014 Chapter 3-1
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