IVT GS-XP12HR-N Service Manual page 25

GSXP12HRN
2. CAUTION IN CHECKING PRINTED CIRCUIT BOARDS (PWB) [GS-XP12HR-N]
2.1. Non-insulated control circuit
The GND terminals of the low-voltage circuits (control circuits for microcomputer and thermistors and drive circuits for expansion valve and relays) on
the control printed circuit board (PWB) are connected to the compressor drive power supply (320-VDC negative terminal). Therefore, exercise utmost
caution to prevent electric shock.
If a measuring instrument used for the test is grounded, its chassis (ground) has the same electric potential as the 0-V probe. Since non-insulated cir-
cuits have the following voltage potential difference from the ground, connection of the grounding wire results in a short-circuit between the 0-V line
and the ground, thus allowing an excessive current to flow to the tester to cause damage.
If the sheaths of the thermistor lead wires or expansion valve lead wires inside the outdoor unit become damaged due to pinching by the front panel
or other metal parts or contacting a pipe, a high voltage can flow and destroy the circuits. To prevent these problems, carefully conduct assembly
work.
Outdoor unit circuits
Terminal board
2
AC230V
1
3
320-VDC line
0-V line
3. DIODE BRIDGE CHECK METHOD
Turn off the power and let the inverter electrolytic capacitor (C9, C10) discharge completely. Then use a tester and check continuity.
When using a digital tester, the (+) and (-) tester lead wires in the table must be reversed.
Reactor Point (E)
+
-
IPM
0-V line Point (F)
Ground
Voltage at point (E)
0-V line voltage (point (F))
4 5 B
Reason
The oscilloscope (chassis ground) has the same electric
potential as the 0-V probe. The entire electronic control section
of the outdoor unit has a voltage potential difference from the
ground as shown in the above diagram. When the oscilloscope
M
is set up, the 0-V line and the ground voltage (ground) will be
short-circuited, resulting in an excessive current flow to cause
Compressor
damage to the oscilloscope or indoor electric circuits.
motor
320V
Needle-type tester
Normal resistance value
(several M )
Value in ( ) is for digital tester.
3 – 4
Do not touch the
cabinet or bring metal
parts into contact with
Danger!!
the cabinet.
Do not connect
the grounding
wire.