Testing Resistance Of The Oven Heater Coil203 - Agilent Technologies 7820A Service Manual

Testing resistance of the oven heater coil
204
Agilent 7820 GC Service
If you believe that your heater coil is cracked or otherwise
damaged and has caused an open circuit, you can check it by
measuring its resistance.
Before proceeding, turn off the main power
switch and unplug the power cord.
Make sure you are properly grounded with an ESD
strap before continuing.
1 Turn the instrument power off.
Disconnect the oven heater leads (P3, P4) from the AC power
board.
Use an ohmmeter to measure resistance at the connectors.
Acceptable resistance ranges (in ohms) are given below.
Acceptable resistances range from the nominal value for a new,
cold heater to +5% from the nominal value.
Resistance goes up approximately 3% after heating
the coil.
Nominal cold heater resistances,
ohms
100 V
120 V
200 V
220 V
220
V-CN
230 V
240 V
n/a = not available
Standard oven
9.07–9.52
9.07–9.52
approximately 25
approximately 25
approximately 30
approximately 25
approximately 25