LG Plasma TV32PC5RV troubleshooting – My service table Today - Ysus board fault

LG 32PC5RV Plasma TV that is not turning ON, just turning on the green LED and then the RED
I did all the procedures; disconnected all the boards leaving only the main board and the source. The problem persisted.
Analyzing the source; only the standby voltage was stable. 
Found two capacitors, and one short transistor and one open resistor. 
Replacing these components, the source started working correctly.
Connecting the TV cards again,  noticed that the source disarmed when connecting the Y-SUS card, without the card connected the TV worked with normal audio, without picture.
Didn’t find any problems on the YSus card, and after several tests forcing the source to connect, I ended up damaging it again. Connected to the main board, the source disarms again.
The behavior is strange.
 When the source is switched on, it is already armed with the 16v, 9Vv, VS and VA voltages armed, which should not happen because the 5V voltage at the RL_ON input to activate the board and the VS_ON input to VS and VA voltages are absent.
  When placing the multimeter or oscilloscope probe on the RL_ON pin to measure this input, the source shuts off, holding only the standby. Removing the probe, the source gun again.
Measured the pull down resistor R717 and the resistor R701 of the input RL_ON and it is also normal.
The voltage Z-SUS that is next to the voltage of VS in the terminal P812 begins with + - 8V in leads around 6 seconds to reach + - 15v gradually rising.
The schematic of this Z-SUS voltage is not in the source diagram. In the output there are some double diodes and some IGBTs and also a circuit with some SMD components that are not in the diagram.
It appears that the signals you indicated to activate the voltages are not correct.
The MULTI_ON signal controls the voltages of 16v 9v 
Signal M5V_ON controls the voltages of 5VSC 5V 5VDET the entire signal management system of the source is controlled by the IC701 MC80F0308 (8-BIT SINGLE-CHIP MICROCONTROLLER) and clear by the main board. 
 Did some tests and found 5v constants on the MULTI_ON line with the source board disconnected from the main board.  
According to the schematic, this MULTI_ON is issued by IC701.
What striked me was the fact that the voltages of 16v, 9v, VS and VA are connected even with the main board disconnected from the source. 
These voltages should be turned off as the power switch is not coming from the main board. 
Only the standby voltage (pin 14 of the P814) should be on. 
"The entire source signal management system is controlled by the IC701 MC80F0308 (8-BIT SINGLE-CHIP MICROCONTROLLER) and clear from the main board".
When connect the power board it no longer has the signals coming from the main and that control the standby state or operation of the source.
In this case they are logical signals that should only be either "0" or "1".
In a logic circuit the inputs must never be left off because the output  is unpredictable.
Performed the following test: Connected a resistance of 4.7k to signal RL_ON and then the other terminal to gnd and then to + 5v standby, to see if the source switches on and off when switching from Gnd to 5V and vice versa and the voltages appear and disappear
Regarding this behavior of the source, it is strange that before that, when the source was connected without the main board, the other voltages except the standby, remained off. This behavior is expected because the resistor R717 (100k) connected between the GND and the pin 14 of the IC701 (RL_ON) does the pull down function, keeping the pin at the logic low level (0V), thus knowing its signal without the main board. 
This also happens with the other inputs of the IC701, the input VS_ON_IN has the R715 and the 5V_ON_IN has the R736. No problem.

 The question of pull down resistances depends.
The IC701 is a micro-controller, and may have internally programmed pull up resistors, which is impossible to tell if it is done by internal software.
I do not know this micro-controller specifically.
This way it seems to me that just by physically testing.
Doing this step by step may draw conclusions and get to the cause of this behavior.
Measured the tension of PFC, so it goes a little further.

PFC voltage: 390V
The tests with the resistor between GND and RL_ON did not disconnect the other voltages, the MULTI_ON line was still at high logic level (5V), the same happened when the same resistor was connected between RL_ON and STANDBY (5v), Source normally connected. By connecting the resistor between RL_ON and GND, pin 14 of the IC701 marked 0v (logic low) and still the source was armed. 
The same happened when connecting the resistor between GND and VS_ON, keeping the voltages of VS and VA actuated.
suspects IC701 is not working.
Checked for any defective solder.
Checked the clock working (with an oscilloscope).
If power is present and stable.
Because some of these signals are present on the main digital board controller and may obey the pre-defined timings.
Connected only the source and the main board.
Removed power and date connections from other circuits.
The problem persists, it will have something to do with the source.
The test with the main board and the source only; it is already done, the green led at the main board lights up and then turns off by turning on the red.
Did not made the measurements at the source to see if the voltages fall or remain. 
The stable power test in the IC I have already done, at least the voltage of VDD is normal and stable.
Now  to test the clock on the X701 to see its status.
To solve the problem of IC701, I have already ordered a scrap plate with this integral IC.
I ran the tests, connecting only the main board and the power supply. At first in this way, everything works normally. 
At the beginning the main board kept the power supply only in standby, the other voltages, 16v, 9v, VS and VA switched off.
The red LED at the main board. 
Removed the M5V_ON terminal from the cable connecting the source to the main board, so the main board kept the power on normally. At times  measured the voltages of VS and VA with approximately 10% of their capacity. But most of the time it was normal and stable.
Turned the M5V_ON terminal on the cable and put the main board and the source back on the TV, turning on the SOM system and the control system (Power, Volume, Channels etc)
 and so the TV turned on, with sound and with power and Volume normally.
Obviously without video because the YSUS card is disconnected. When I connect it the TV goes into standby.
And now, the source is normal?
In my view it is not because it should obey the commands without the main plate and not obey. It looks like the main board is managing to handle it normally.
Although I seem to have failed the signals, I remembered the timing issue and then done that test. 
In my view if the source works correctly, when fully connected to the main board, this may mean that the problem should not be in those circuits; unless the source behaves differently with loads. 
Focussed attention on the YSUS board and why it go into protection when turn it on.
One thing I noticed that may be affecting the operation with the YSUS connected to SOURCE is the source Z-SUS output that does not appear to be stable. 
The source Z-SUS output starts at 8V and takes + or - 7 seconds to reach 15V reaching up to 16.6V.
The source is not in the schematic. 
Done some tests to identify if any specific line of the terminal P812 is disarming the circuit because until the moment I did not find any change in the YSUS. 
At the input of the coil at the YSUS Z-SUS input line there was a malfunction in the solder, it appears that an overload has damaged the solder. 
Did some more tests without being able to finish something about the problem. 
Tests were done with the main board connected to the source, and the YSUS connected to the source, but not connected to the main board. In this way the TV remains on. Connecting YSUS to the main board, the TV switches off. 
Turned on the TV with YSUS disconnected from the SOURCE and the multimeter connected to the ZSUS output of the source. It is possible to see that when the TV is turned on, the audio comes (to hear the TV squeak) and the ZSUS output voltage starts at just over 1V and then drops to about 600mV. Turning off the TV, the voltage drops.
Done a test with YSUS connected to the source, But not connected to the main board. In this test, the ZSUS voltage of the source reaches a maximum of 13.2V. The voltages of VS, VA and 5V of YSUS are normal, only problem is this voltage [15V.] 
To confirm this part of the source that you think is in fault record: 
The voltage of PCF in C617 C618 
The voltages and ripple in C202 C207 and Q201 
If everything is OK,  the problem should be in the circuit of Ysus or circuit buffers in short. 
Tried by turning off the buffers and check if the TV stops turning OFF. 
The PFC voltages in the two capacitors were normal. Voltages in the components and ripple in C202, C207 and C201 too are normal. 
The tests without the lower buffers already did and the TV turns off. 
The fact  the flat was connected to the P813 connector (screen printing of the PCB) should not light something on the screen.

So it seems to me that the problem is with the YSus board. 
Replaced the YSus board. Tested OK
Very sad to say that it is very difficult for any service technician to repair LG brand devices, as there is no sufficient details, or a clear schematics published by them. All the schematics will look like it was drawn by some beginner students in electronics. A reputed company shouldn't be so.  


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