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A
[2] PD (POWER-DOWN) DIAGNOSIS OF FAILURE ANALYSIS
How to Distinguish the PD (Power-Down)
About the LED for checking causes of power-down
No LED for checking causes of power-down is provided for the POWER SUPPLY Unit of the MR.
However, by checking the waveforms at terminals of the microcomputer, whether a power-down was caused by
failure in the POWER SUPPLY Unit, and if it was, which power system among the four was in failure can be inferred.
The points at which to check waveforms and how to distinguish power-down causes are described below:
<Points at which to Check Waveforms>
B
Waveforms between Pin 3 of CN801 and GND (secondary radiator, display chassis, etc.)
Refer to the section "Note on Removing the POWER SUPPLY Unit from the Chassis and Method for Resettig Standby
Power Latchup" in the "7.2 DISASSEMBLY".
<How to Distinguish>
If a power-down was caused by failure in the POWER SUPPLY Unit, a pulse waveform is output at the above-mentioned
points. (It is assumed that STB3.4 V power is properly output.)
By counting the frequency of "Lo" in the pulse waveform, the cause of power-down can be identified.
Frequency
of "Lo"
Output Voltage
C
Once
Twice
3 times
4 times
*How to distinguish OV and UV:
If the first "Lo" duration of a pulse is long (1 s), the cause is OV.
As the three output voltages are electromagnetically linked and interact with one another,
the frequency may vary among 1-3, depending on the type of power-down.
Examples:
UV alarm
D
3.3V
OV alarm
3.3V
E
F
58
1
2
Cause
Overvoltage (OV) or Undervoltage (UV)
+12V
+17V
+6.5V
Protection against overheat
1
2
3
4
1
Reiteration
0.5s 0.5s 0.5s 0.5s
1s
OV
1
2
3
4
Reiteration
2
3
OV or UV *
OV or UV *
OV or UV *
2 GND
GND
KRP-M01
3
4
4

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