Inverter Power Supply (U); Temperature Thermistor - Panasonic NN-SF550M Service Manual

NN-SF550M
7.4.

Inverter power supply (U)

DO NOT try to REPAIR H.V. Inverter power supply (U).
Replace complete H.V. Inverter(U) Unit.
WARNING: HIGH VOLTAGE
Test if failure codes H95, H97 or H98 appear when performing
the following procedure. It is recommended to use an AC line
input current ammeter for testing.
Test 1
1. With the oven unit's AC power supply cord is unplugged
from the wall outlet, unplug the 2 pin H.V. connector CN703
from the magnetron tube.
2. Place 1 liter of water load into oven cavity.
3. Plug in the oven's AC power supply cord into outlet.
4. Program DPC.
a. Press Clock pad once.
b. Press Timer pad once.
c. Press Start pad once.
d. Press Power Level pad once.
5. Program oven at High power for 1 minute and press [Start]
pad.
a. After approximately 23 seconds, oven stops operating.
b. During oven
approximately 0.5 to 1A. If both a and b are OK,
proceed to test 2.
INPUT CURRENT
Unplug CN703
Test 2
Continued from Test 1
1. Unplug the oven's AC power supply cord from outlet.
2. Unplug 3 pin connector CN701. CN703 remains unplugged.
3. Plug in the oven's AC power supply cord into outlet.
4. Program DPC.
a. Press Clock pad once.
b. Press Timer pad once.
c. Press Start pad once.
d. Press Power Level pad once.
operation, the input current
FAILURE CODE
0.5 to 1A Oven stops in 23
seconds after started.
5. Program oven at High power for 1 minute and press [Start]
pad.
a. After approximately 3 seconds, oven stops operating.
b. During oven
approximately 0.4A.
Unplug CN701
If both a and b check OK, the Inverter Power Supply (U) can be
determined to be OK.
7.5.

Temperature thermistor

These sensor monitors the heat produced by the heater circuit
and maintains the magnetron temperature which user had
selected. Normal room temperature 10°C to 30°C, the reading
across the temperature thermistor should be from 35KΩ to 110
KΩ.
If the resistance reading is out of the range stated here, the
thermistor is detective and must be replaced.
It is also possible to display thermistor level by taking the
following steps.
1. Program the DPC into TEST MODE (Plug-in oven → press
Clock pad once → press Timer
Start pad once → press Power Level pad once).
2. Program oven at Standing Time for 1 minute and press
[Start] pad.
3. Press Power Level once, the thermistor level reading will
shown on the display.
The normal reading should be in the range of 16-230.
is
16
operation, the input
INPUT CURRENT FAILURE CODE
0.4A Oven stops in 3
seconds after started.
pad once → press
current is