Testing The Transformer; High-Voltage Diode; Testing The High-Voltage Diode - TurboChef Eco Service Manual

38 OVEN SYSTEMS

Testing the Transformer

DANGER: Never attempt to measure the
secondary voltage values of the transformer.
Lethal voltage will be present.
1. Disconnect the AC power source and discharge
the capacitor.
2. Disconnect all the wires going to and from the
transformer.
3. Use an ohmmeter to check the resistance of the
primary and secondary winding. Refer to Figure
78, below, to determine if the transformer is
good. If the resistance is different than the table
indicates, replace the transformer.

High-Voltage Diode

The high-voltage diode (Figure 77) is assembled by
connecting several 1000-1500 volt semi-conductor
diodes in a series to increase the reverse voltage
capability.
Figure 77: High-voltage Diode
In the circuit, the high-voltage diode conducts
to prevent the filament voltage from becoming
positive, thus as the high-voltage winding of the
transformer goes to a peak of 2400 volts, the
high-voltage capacitor is charged to 2400 volts.
High Voltage
Transformers
104137
105258
105244
Figure 78: Transformer Resistance Table
Primary Voltage, Frequency, Taps,
and Resistance
208 VAC, 60 Hz, 1 & 2, 0.93-1.14 Ω
240 VAC, 60 Hz, 1 & 3, 1.11-1.135 Ω
230 VAC, 50 Hz, 1 & 2, 1.03-1.26 Ω
200 VAC, 50/60 Hz, 1 & 2, 0.75-0.92 Ω
When the high-voltage winding starts to go toward
negative, the high-voltage diode becomes non-
conducting with the charged high-voltage capacitor
in series with the high-voltage winding. When the
transformer gets to its negative peak of -2400 volts,
the voltage applied to the filament is -4500 volts.
The high-voltage diodes are rated at 16 kVDC.

Testing the High-Voltage Diode

DANGER: Never attempt to measure high
voltage directly. Death or serious injury could
result.
1. Disconnect the oven from the power source.
2. Fully discharge the capacitor.
3. Connect the voltage meter in series with the
high-voltage diode.
4. Using a multimeter set to DC voltage, connect
one meter lead to one side of a 9-volt battery
and the other lead to one side of the high-
voltage diode.
5. Connect the other side of the 9-volt battery to
the other side of the high-voltage diode. DC
voltage should be present on the meter in only
one direction.
6. Switch the meter leads on the high-voltage
diode, which will cause the opposite reading
to be visible. Depending on the voltage of the
battery, voltage between 5-7 VDC should be
present in only one direction and 0-0.1 VDC in
the other direction.
Secondary Taps to Frame Resistance
4 & Ground, 63.14-77.18 Ω
3 & Ground, 66.66-81.48 Ω
3 & Ground, 59.83-73.13 Ω