TOSHIBA PDP - 42HP83 _ POWER SUPPLY SHUT DOWN DIAGNOSIS
The power supplies used in this series TVs consists of four boards. Since troubleshooting should be done at board level to determine which board have the fault. A modular level approach is given here.
The supply boards are Main Power, Sub Power, Low B1 and Low B2.
The Main Power Board generates a verity of supply voltages use through out the unit. See the tables.
|
MAIN POWER BOARD _ CN201
|
|
|
1
|
171.3VDC 500K
|
|
2
|
171.3VDC 500K
|
|
3
|
170.8
1M
|
|
4
|
NOT CONNECTED
|
|
5
|
0
|
|
6
|
0
|
|
7
|
0
|
|
8
|
69.9
>2K
|
|
9
|
0
|
|
CN202
|
|
|
1
|
3.07V
|
|
2
|
2.43V
|
|
3
|
4.87V
|
|
4
|
0
|
|
5
|
2.19V
|
|
6
|
20.28V
|
|
P808
|
|
|
1
|
11.88
|
|
2
|
11.88
|
|
3
|
11.88
|
|
4
|
0
|
|
5
|
0
|
|
6
|
0
|
|
7
|
.131
1.4K
|
|
P807
|
|
|
1
|
20.28
|
|
2
|
20.28
|
|
3
|
20.28
|
|
4
|
0
|
|
5
|
0
|
|
6
|
0
|
|
7
|
31.9
|
|
8
|
11.88
|
|
9
|
4.88
|
|
10
|
3.3
|
|
11
|
3.25
|
|
12
|
4.87
|
|
13
|
.13
|
|
P809
|
|
|
1
|
25.9
|
|
2
|
25.9
|
|
3
|
25.9
|
|
4
|
25.9
|
|
5
|
0
|
|
6
|
0
|
|
7
|
0
|
|
8
|
0
|
SUB POWER BOARD VOLTAGES
|
CN805
|
|
|
1
|
69.9
|
|
2
|
69.9
|
|
3
|
0
|
|
4
|
0
|
|
5
|
0
|
|
CN201A
|
|
|
1
|
3.05
|
|
2
|
2.42
|
|
3
|
4.88
|
|
4
|
0
|
|
5
|
3.2
|
|
6
|
20.28
|
|
CN808
|
|
|
1
|
3.45
|
|
2
|
3.45
|
|
3
|
0
|
|
4
|
0
|
|
5
|
5.07
|
|
6
|
0
|
|
7
|
0
|
|
8
|
0
|
|
9
|
3.2
|
|
10
|
0
|
|
|
CN201A
|
|
171.2
|
1
|
|
171.2
|
2
|
|
171.2
|
3
|
|
NOT CONNECTED
|
4
|
|
0
|
5
|
|
0
|
6
|
|
0
|
7
|
|
69.9
|
8
|
|
0
|
9
|
|
CN806
|
|
|
1
|
69.8
|
|
2
|
69.8
|
|
3
|
0
|
|
4
|
0
|
|
5
|
0
|
|
CN802
|
|
|
1
|
5.07
|
|
2
|
14.88
|
|
3
|
0
|
|
4
|
0
|
|
5
|
150.3
|
|
6
|
0
|
|
7
|
0
|
|
8
|
0
|
|
9
|
0
|
|
10
|
171.2
|
|
11
|
171.2
|
|
CN803
|
|
|
1
|
5.07
|
|
2
|
14.87
|
|
3
|
0
|
|
4
|
59.7
|
|
5
|
0
|
|
6
|
0
|
|
7
|
0
|
|
8
|
0
|
|
9
|
0
|
|
10
|
0
|
|
11
|
0
|
|
12
|
0
|
LOW P1 POWER BOARD VOLTAGES
|
P810B
|
|
|
1
|
3.18
|
|
2
|
4.88
|
|
3
|
3.24
|
|
4
|
3.29
|
|
5
|
0
|
|
6
|
0
|
|
7
|
9.18
|
|
8
|
9.18
|
|
9
|
0
|
|
10
|
0
|
|
11
|
5.15
|
|
12
|
5.15
|
|
P807A
|
|
|
1
|
20.26
|
|
2
|
20.26
|
|
3
|
20.26
|
|
4
|
0
|
|
5
|
0
|
|
6
|
0
|
|
7
|
31.9
|
|
8
|
11.89
|
|
9
|
4.87
|
|
10
|
3.29
|
|
11
|
3.249
|
|
12
|
4.88
|
|
13
|
.131
|
|
P823B
|
|
|
1
|
9.19
|
|
2
|
0
|
|
3
|
5.14
|
|
4
|
5.21
|
|
5
|
0
|
|
6
|
3.79
|
|
P811B
|
|
|
1
|
4.86
|
|
2
|
0
|
|
3
|
0
|
|
4
|
0
|
|
5
|
0
|
|
6
|
31.9
|
|
7
|
11.89
|
|
8
|
6.66
|
|
9
|
3.47
|
|
10
|
3.47
|
LOW B2 POWER SUPPLY BOARD VOLTAGES
|
P816A
|
|
|
1
|
3.43
|
|
2
|
3.43
|
|
3
|
3.43
|
|
4
|
0
|
|
5
|
0
|
|
6
|
0
|
|
7
|
3.42
|
|
8
|
3.42
|
|
9
|
3.42
|
|
10
|
0
|
|
11
|
4.84
|
|
12
|
0
|
|
13
|
9.06
|
|
P817B
|
|
|
1
|
4.8
|
|
2
|
0
|
|
3
|
0
|
|
4
|
0
|
|
5
|
0
|
|
P819
|
|
|
1
|
11.1
|
|
2
|
0
|
|
3
|
.09
|
|
P808A
|
|
|
1
|
11.88
|
|
2
|
11.88
|
|
3
|
11.88
|
|
4
|
0
|
|
5
|
0
|
|
6
|
0
|
|
P818
|
|
|
1
|
11.1
|
|
2
|
0
|
|
3
|
.09
|
If a power supply panel has been replaced or in the unlikely event of a Plasma Panel change, certain poser supply adjustments should be done. The adjustments Vs, Va, Vsc, Vset and Ve determine the voltage supplied to the plasma screen, and are controlled by a variable resistor located on the supply panels. As incorrect voltage level may cause shutdown or screen damage, it is important to measure the DC voltage levels at each test point prior to adjustment. The voltage requirements are clearly marked on the display panel.
Shutdowns in this Plasma receiver can be divided into tow categories. The unit can shut down due to a problem, such as an inoperable fan, or it can shut down due to an over-voltage condition. Both of these shutdowns are noted by the microprocessor, but can be identified by two different error symptoms.
- Shut downs such as the lack of a fan rotation simply cause the microprocessor to turn of the unit off and exhibit an error code by blinking the Power LED. When these occur, the unit will be allowed to restart by turning it off and back again on. In this situation normally have enough time to troubleshoot the unit and in some cases read the error codes in the service menu.
- Over-voltage shut down is a function of a distribution system and latches the unit off when it occurs. It will not attempt to start again, until it is unplugged and AC is applied again. In addition to latching the unit off, the shut down usually occurs immediately, generating a dead set with no indication, other than blinking power LED indicating a shut down condition. This indicates a Power Supply Related problem.
CAUSES OF SHUTDOWN [BOARD LEVEL]
- The system monitors most of the DC sources being developed by the regulators on the Low B1 & B2 power supply boards. When an over voltage condition is detected by this shut down circuit, the protect line will rise, causing the unit to shut down and signalling the the microprocessor that this has occurred.
Shut-Down Circuitry
- When the protect line in this circuit rises, the gate of SCR D819 will also rise, and cause the SCR to conduct and to apply a DC voltage to the base of Q819, which in turn will conduct, and the Power TV or Power On Line will be pulled low. This cause the Power Relays in the unit to open. As well as opening the relays and shutting the unit down, when Q819 pulls the Power Line, Low signalling the microprocessor that the unit has shut down and blinking LED display indicating shut down will begin. The protect line that operates this shut down monitors five different voltage sources.
- On the Low B1 Power Supply Board, the 6.5VD, the 3.3VD, the 5.2V2 and the 9 volt sources are monitored.
- On the Low B2 Power supply board, the 3.3VS1 source is monitored. These two sources are monitored by Zener diodes in series with steering or blocking diodes and a reisistor connected between the product line and the source.
- For an example: Monitoring system as it applies to 5V2 source on the Loq B1 board.
Since troubleshooting is done to Board Level, all that need to
be done is to determine which of the two boards is causing shut down.
The only one source is monitored on the Low B2 board. So need to make
only one measurement to determine the cause to board level.
That measurement involves the [3.3VS1] source located on the Low B2
supply board
To measure and make a determination
Using a DC oscilloscope , measure the voltage developed across
resistor [R872] at turn On. Connect properly the leads of scope first
to the measuring points, remove the AC to reset the unit and reapply
again.
If the Low B2 board is defective, scope will measure a momentary
voltage across R872 when the unit is turned ON. This measurement can
also be done with a digital multimeter, set to voltage hold mode.
What happens here is, the break over point of the Zener diode
[D872] is 4.3Vdc. If it conducts due to an over voltage on the [3.3VS1]
supply line, this voltage will appear at its Anode. After it passes
through [D873], it will be reduced approximately (0.6V) due to the diode
junction. [R872] & [R819] form a voltage divider network. Both of
them are 1000Ohms, meaning, the voltage appear across each resistor
will be ~ 1/2 of the voltage appearing at the Cathode of D873, [4.3 -
0.6 = 3.7]. Half of this 3.7V is ~1.8Vdc.
