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Impinger I -–1000 Series Service Manual - International 44
Time/Temp Display 12.6 VAC Power Supply Measure the transformer primary inoperative for a
nominal 120 VAC input. Measure the secondary
voltage output which will be 12.5 to 15 VAC
normally. Recheck secondary output at rear of
Time/Temp Display. Terminals 1 to 3 should read
12.5 to 15 VAC. Terminals 1 to 2 and 2 to 3 should
be exactly 1/2 of the reading across 1 to 3. If you
do not get the above secondary readings, replace
the transformer. If 120 VAC primary voltage is not
available, refer to the schematic and trace circuit
for incoming power failure. There is a 4 amp fuse in
each red secondary lead. These may be jumpered
(for test only) to determine if they are defective or
intermittent.
NOTE: (Dual Belt Ovens) Dual belt ovens utilize a double pole double throw
switch, which allows either of the optical encoders
to be read from a single Time/Temp. Display.
Check switch and replace as needed.
NOTE: Time/Temp displays
use two types of temperature
sensor, Thermistor Probe – 2
yellow wires Thermocouple
Probe 1 red wire and 1 white
wire
Place your pyrometer thermocouple into the center
between fingers T2 and T3 in the oven. Disconnect
the yellow tipped thermistor leads from the
time/temp. terminals 9 and 10. Measure the
resistance of the thermistor probe. See chart on
page 72 for proper resistance readings.
Thermistor Probe Inspect the thermistor bulb for its proper location in
its spring holder. Check for short in leads where
they enter the sensor bulb. Also check each
thermistor lead for short to ground.
Thermocouple Probe Place your pyrometer thermocouple into the center
between fingers T2 and T3 in the oven. Connect
temperature meter to thermocouple at terminals 9
& 10 on back of the time/temp display (Be sure to
maintain proper polarity on thermocouple
connections.) Compare actual oven temperature
with the reading at the time/temp display. If the
temperature readings match, recalibrate or replace
time/temp display. If the readings do not match,
replace thermocouple probe.
Erratic time/temp display If strange or unusual behavior is experienced such
as a rolling of numbers, lock up at a given number,
first check for a display circuit lock up. This can be
caused by a voltage spike or surge. To eliminate
this condition remove power from the time/temp.
display by shutting off the main fan switch, or if
display stays on, (older models) circuit breaker
interruption may be required. This should eliminate
the problem. If the problem continues, jumper the
two fuses in the red wires leading from the 12.6
VAC transformer to the display. If this does not
solve the problem, it may be coming in through the
commercial power lines. Suggest that customer
contact his power company for evaluation.
Temp Display out or
inaccurate
Temp Display inaccurate
erratic, or inoperative
Perform the power supply check, the thermistor
probe check, and then perform the time/temp
simulator test. Refer to page 72 for instructions.
Remember, when using the time/temp simulator,
remove all the leads from the back of the display
except the 3 power leads. After completion of this
test and if reinstalling back into the oven, the dip
switches must be reset for oven operation.