Master Electronics Repair !

Welcome to Master Electronics Repair! website.Here you will find:Service Modes, Circuit Diagrams,Service manuals, Firmware Update procedure, Disassemble procedure, Universal remote control setup codes, Troubleshooting, Diagnosing, Measuring, and more.... of many of LCD/LED TV/Displays,others various electronic apparates,trough many technical notes and tips/tricks to help repairing/fixing Troubles/ faults,for electrical technicians.This site helps you to save the Earth from electronic waste!

Richtige Fernseher haben Röhren!

Richtige Fernseher haben Röhren!

In Brief: On this site you will find pictures and technical information about Service Modes, Circuit Diagrams, Firmware Update procedure, Disassemble procedure, Universal remote control set-up codes, Troubleshooting and more....

If you go into the profession, you will obtain or have access to a variety of tech tips databases HERE IT IS Master Electronics Repair !.

These are an excellent investment where the saying: 'time-is-money' rules. However, to learn, you need to develop a general troubleshooting approach - a logical, methodical, method of narrowing down the problem. A tech tip database might suggest: 'Replace C536' for a particular symptom. This is good advice for a specific problem on one model. However, what you really want to understand is why C536 was the cause and how to pinpoint the culprit in general even if you don't have a service manual or schematic and your tech tip database doesn't have an entry for your sick TV or VCR.

While schematics are nice, you won't always have them or be able to justify the purchase for a one-of repair. Therefore, in many cases, some reverse engineering will be necessary. The time will be well spent since even if you don't see another instance of the same model in your entire lifetime, you will have learned something in the process that can be applied to other equipment problems.
As always, when you get stuck, checking out a tech-tips database may quickly identify your problem and solution.In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts.

Happy repairing!

Today, the West is headed for the abyss. For the ultimate fate of our disposable society is for that society itself to be disposed of. And this will happen sooner, rather than later.

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..............The bitterness of poor quality is remembered long after the sweetness of todays funny gadgets low price has faded from memory........ . . . . . .....
Don't forget the past, the end of the world is upon us! Pretty soon it will all turn to dust!

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Thursday 21 March 2019

LG 47LG90 LED LCD TV - POWER SUPPLY TROUBLESHOOTING

SMPS PWB OPERATIONAL TROUBLESHOOTING
Ac voltage is supplied to the Power Supply at Connector SC100. AC Detect is generated and should be present at connector P201 pin 8 (5V). The AC input also generates a Hot Ground primary power supply that runs in two states, Stand-By (156V) and Run (386V) measured at Fuse F101. This primary voltage develops all other voltages that are output from the power supply. During Stand-By, the 5 Volt Standby should be present at connector P201, Pins 9,10,11 or 12. If Missing remove AC Power and unplug Connector P201, apply AC Power and recheck for presence of both 5 Volt Standby and AC Detect. Loss of either 5 Volt Standby or AC Detect would be a Power Supply Failure. Presence of 5 Volt Standby and AC Detect would be an indication of a failure on the Main Board. Suspect a possible short circuit loading the supply. Remember to observe the Front Power Indicating LED this may save some time. A lit LED most likely indicates the Stand-By 5V voltage is present.

A loss of the AC detect line will prevent the front power LED from lighting, because, it is driven by I2C bus communication.

The Main Board sends two commands to the Power Supply Board one being PWR the other is INV ON. These two voltages are used to control the power on turn on sequence. First via PWR (Pin 19) also known as RL ON activates the 24Volt to the Inverters and the 16 Volt and 12 Volt lines to the Main board. The 2^nd command is INV ON. It passes through the Power Supply to the Inverter Boards to turn them on. If either command voltage (PWR or INV ON) is missing it will result in a no picture symptom. These voltages can easily be checked with the voltmeter. Remove AC Power, unplug Connector P204, reapply AC Power and press the ON-OFF Button on either the Remote Control or Power Button on the Unit. Watch for the Power ON LED to change color from red to blue. This is an indication the PWR Signal was created on the Main board. Check P800 or P201 pin 19 for the PWR command (2.8V) to the Power Supply. Check P201 for 16V (Pins 1 or 2)and 12V (Pins 5 or 6). Check P204/P205 Pins 1,2,3,4 or 5 for the presence of the 24 Volt Supply. Confirm Pin 12 of P204/P205 went to 3.3V. This is the INV ON signal needed to turn on the Inverters and light the backlight LEDs.

Following the simple steps can easily solve problems with either voltage.

LOW VOLTAGE TEST
AC Should not be applied at any time while adding resistors or while unplugging connectors as damage to the circuit PWB may occur.

The SMPS PWB “MUST” be producing STBY 5V on pins 9, 10, 11 or 12 (5V).
The SMPS PWB “MUST” be generating ACD (AC Detect) Pin 18 check for 5V.
If the conditions (a) or (b) above are not met, the SMPS PWB is defective and must be replaced. There is no need to continue with the test.
Unplug P800 on Main PWB and P204, P205 to the inverters.

TEST 1:

Add a 10K resistor between (5V STBY) pin 9, 10, 11 or 12 and Pin 19 (PWR). Apply AC. This will turn on the power supply.
Check that the 16V and 12V power supplies are turned on, P201 (16V pins 1 and 2) (12V pins 5 and 6)
Check that the 24V (Inverter B+) is turned on P205 and P204 pins 1~5.
Remove AC power. Reinsert the plugs P204/P205 to the inverters.

PWB BACKLIGHTS TEST

P800 Connector disconnected from the Main PWB. Apply AC after adding jumper.

Continue if the 1^st test was successful. Leave original 10K resistor in place.

Add a jumper wire between Pin 20 (INV On/Off) to Pin 19 (PWR).
Apply AC Power. This simulates a Power On and Backlight On command. Observe the Backlights.
If normal, the backlights should turn on. (They will be dim.)
If no backlight activity, reconfirm the 24V is being generated and output on P204/P205 connector Pins 1~5. If not, unplug P204 or P205 and recheck. If not SMPS is defective. If yes, Inverter is loading down the 24V line.
Confirm the INV On/Off line Pin 20 is going to 3V. Confirm the Inverter On command is leaving P204/P205 Pin 12.
If all the above is normal, refer to the Inverter section to check voltages on the Inverters.

POWER SUPPLY PWB BACK-LIGHTS TEST

Using the Power Supply (SMPS) Voltage Label (Silk Screen)

Using the (Silk Screen) Label can assist when dealing with an over current situation. Normal loads will keep the current reading under the Label’s maximum currents output reading.

The AC input Fuse draws a maximum current 5 Amps.
The 5.2V output (Stand by 5V) maximum output current 6.5 Amps.
The 12V output (Video Processing and T-CON board B+) maximum output current 2.25 Amps.
The 16.5V output (Audio) maximum output current 1.3 Amps.
The 24V output (Inverters) maximum output current 11 Amps.