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Cabinet Service Procedures
1-1
1 Functional Description
1.2 Theory of Operation
The cabinet operates on 208-250VAC 50 or 60 cycle single-phase power. The main switch activates
a relay, which supplies line voltage to two distribution boards, three cooling fans and a power
supply. The power supply provides 5VDC to the master control board and the distribution boards.
A ribbon cable connects the master control board to both distribution boards. Ribbon cables also
connect the distribution boards to the displays. The resistance of RTD’s, attached to the heater
plates, is monitored by the distribution boards. The board switches power through solid-state relays
to the heater plates when the resistance, which is used as an indicator of temperature, falls out of the
range for the product held in the cabinet.
The switch, relay, master control, master control board, LON board, LON filter, cooling fans and
power supply are mounted under the top of the unit. The cabinet is programmed using the key pad
on the front bezel.
Timer keys
Note: Theillustrationsfor
theseserviceprocedures
areofthe6‐rowfullsize
UHC
‐
HD
.
Row Mode key
Timer: displays on row
board remaining time for
all active timers.
Temperature: displays on
row board plate
temperature, alternating
between top and bottom.
Power switch
Timer key
Master Control Display