Lincoln Dual Technology Finisher 1921, Service Manual

Page: 7 / 24

DTF – 1920 Series Service Manual
7
Control transformer Check for 208/240VAC supply to the primary of the
control transformer. If no voltage is present, trace
wiring back to the main power switch. If voltage is
present, check for 24VAC at the transformer
secondary. If there is primary voltage, but no secondary
voltage, replace the control transformer.
Oven control Check for 24VAC supply to control. If no voltage is
present, trace wiring back to control transformer. If
24VAC is present, check for a read-out on the display.
If there is 24VAC supplied, but there is no read-out on
the control display, replace the oven control.
If there is a read-out on the control, set the control to
maximum temperature (see installation operations
manual for temperature adjustment). With the control
set at maximum temperature, check for supply voltage
to the oven control at terminals J3-12 and J3-3. If there
is no voltage present, trace wiring back to the air
pressure switch. If there is voltage present, check for
output voltage at the Main heater relay (R1). If there is
voltage at the Main heater relay, proceed to “Main
heater relay” for next check. If there is no voltage at the
Main heater relay, trace wiring back to the oven control.
If there is no voltage output at the oven control, check
the read-out on the control. If the control reads
“PROBE FAIL”, this indicates that the thermocouple
has failed or become disconnected from the oven
control.
Thermocouple Check to be sure that the thermocouple is securely
connected to the oven control. If the thermocouple is
connected to the oven control, and the control indicates
“PROBE FAIL”, disconnect the thermocouple from the
oven control and measure the resistance of the
thermocouple. The thermocouple should read approx.
11
Ω . If these readings are not achieved, replace the
thermocouple. If these readings are correct, proceed.
Oven control If the thermocouple checks good, but the oven control
display indicates that there is a thermocouple failure,
replace the oven control. If the oven control indicates a
temperature reading but the oven will not heat,
proceed.
Thermocouple WITH POWER ON AND THERMOCOUPLE
ATTACHED TO THE OVEN CONTROL: Measure the
DC millivolt output of the thermocouple. Refer to the
thermocouple chart (located in the “Removal” section of
the manual) for proper millivolt readings. If these
readings are not achieved, replace thermocouple.
Oven control If the thermocouple checks good, but there is no
voltage output to the Main heater relay, replace the
oven control. If there is voltage output to the Main
heater relay, proceed.
Main heater relay Check for supply voltage to the relay coil. If voltage is
present and the relay will not activate, replace the Main
heater relay. Also check each relay contact for high
voltage input and output.
Heating element(s) Check the Amp draw on each power leg for proper
load. Check the specification plate for rating
information. If the amp draw is high or low, check the
individual elements for opens, shorts and proper
resistance.
WITH POWER OFF: To check resistance of the
elements, remove all leads from the elements and use