Duke DSO 500, Service Manual

Page: 29 / 80

29
HEATERS AND THERMAL
CUTOUTS
The three heaters, Figure 11A, are used to heat
the oven. These heaters are controlled by the
control board through relays K1, K2, and K3. The
high limit and aux thermal cutouts, Figure 11B,
are connected in series with the heaters and the
input power source through the line fuses. If the
temperature exceeds 274°C all heaters are cut-
out of the circuit through the aux thermal cutout.
If the temperature exceed 302°C the high limit
thermal cutout opens and disconnects all the
heater elements.
Both thermal cutouts are self-resetting.
Location and Access
The heaters and thermal cutouts are located
inside a housing at the right rear of the oven.
The right side panel, top panel and rear panel
will need to be removed.
Safety Issues
WARNING
THE HIGH VOLTAGE CAPACITOR RETAINS
THE 2.5 kVDC CHARGE EVEN AFTER THE
OVEN IS DISCONNECTED. THIS CAPACI-
TOR MUST BE DISCHARGED BEFORE
WORKING ON ANY COMPONENTS WHEN
THE TOP COVER IS REMOVED.
• Electrical supply of 208/240 VAC to the
control transformer when POWER switch
is in ON position
• Main POWER switch has 208/240 VAC
present on the input side whenever the
oven is connected to the input power
source
Tools required
• Flat blade screwdriver to remove pan-
els.
• Phillips head screwdriver to remove
heater panel and enclosure.
Figure 11A. Heating Coils
COMPONENT OVERVIEW