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8-74. Normal Operation
8-75.
When the oven is tested under normal conditions (-25°C ambient temperature) it will initially draw
380 to 490 mA. After 5 to 10 minutes the oven current will start to drop. Over the next 10 to 15
minutes the oven current will fall to the 60 to 150 mA range where it will stabilize. The oven circuit
should not oscillate.
DO NOT OPERATE THE OVEN CIRCUITS WHEN THE OVEN MASS IS
OUTSIDE OF THE OSCILLATOR INSULATED HOUSING. DOING SO
WILL OVERHEAT THE OSCILLATOR CIRCUITS INSIDE THE OVEN
MASS AND CAUSE PERMANENT DAMAGE. ALL OVEN TEST POINTS
ARE A V AILABLE WITH THE OVEN MASS AND OVEN CONTROLLER
CIRCUIT INSIDE THE HOUSING.
WHEN OSCILLATOR COVER AND INSULATOR ARE REMOVED
THERMAL FUSE WILL NOT PROTECT CIRCUIT FROM OVER-
HEATING. APPLY OVEN POWER ONLY WHEN ACTUALLY MAKING
MEASUREMENTS FOR TROUBLESHOOTING OR AS DIRECTED IN
TROUBLESHOOTING TREE,
8-76. TROUBLESHOOTING
8-77.
Table 8-2
is a troubleshooting' tree for the oven circuits. The troubleshooting procedure separates
the different functional circuits by monitoring the oven supply current during different operating
conditions. For example, if the warm-up current is excessive, this indicates a trouble in the warm-
up current limit circuit, or the current control and heater circuit. If shorting the thermistor reduces
the current being drawn from the power supply, this indicates the current control circuit is
operating and the problem is most likely in the warm-up current limit circuit.
8-78.
As with most troubleshooting trees this is intended to be a guide to the trouble area. It is not a
substitute for technical skill in isolating the faulty components.
Table 8-3
(next to schematic diagram) gives normal circuit voltages during warm-up, operation,
8-79.
and when thermistor RT1 is shorted to ground. Use this table during troubleshooting.
8-80. Troubleshooting Cautions
8-81.
When oven current is excessive, turn on the power supply only long enough to make the
necessary measurements. Do not leave power on if the oven is drawing excessive current. With
the housing cover and foam insulator removed, the thermal fuse (F1) cannot protect the circuits in
the oven mass from overheating and damage.
8-82. Flex Damage
8-83.
If a tear in the flex circuit occurs, the tear can continue until a trace is broken. To stop a tear, use
a pair of scissors and cut around the tear. DO NOT CUT A SHARP CORNER as this will cause a
stress concentration allowing the tear to start again. A hole-punch may also be used. Punch a
hole in the flex so as to remove the forward end of the tear.
56
WARNING
TABLE
8-2.
Model 10811A/B
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Table of Contents
Troubleshooting
