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Impinger I -–1000 Series Service Manual - Domestic
30
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 in
Section D 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 51 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.
Time display inaccurate
erratic, or inoperative
Perform all checks as in the above evaluation. If
the time check is okay, refer to the next section
optical encoder.
Optical Encoder The above time/temp test should have already
been performed. Remove dust cover from the
gearmotor and inspect the coupling and encoder
disc. The coupling set screws should be tight and
not slipping on the motor shaft or the tach.
generator shaft. The encoder disc should be firmly
attached to the coupling and not warped. Check
the positioning of the optical encoder disc. The disc
should not be touching the optical encoder
assembly and the encoder assembly should be
mounted so it is squarely facing the coupling shaft.
This is to allow the infrared beams to be broken by
the encoder disc. If all this is okay, then replace the
optical encoder assembly.