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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All posts are presented here for informative, historical and educative purposes as applicable within fair use. NOTHING HERE IS FOR SALE !

Thursday, 21 March 2019

LG 37LH55 - LCD TV - POWER SUPPLY - TROUBLESHOOTING - VOLTAGE AND DIODE CHECK VALUES

MAIN POWER SUPPLY [SMPS]

Ac voltage is supplied to the Power Supply at Connector SC100. This set does not use AC Detect. The AC input generates a Hot Ground primary power supply that runs in two states, Stand-By (168) and Run (380V) measured at Fuse F501 from Hot Ground. This primary voltage develops all other voltages that are output from the SMPS. During Stand-By, the 5 Volt Standby (5V_ST) should be present at connector P201, Pins 7,8,9 or 10. If Missing remove Power and unplug Connector P201, apply AC Power and recheck for presence of 5V_ST. Loss of 5V_ST would be a SMPS Failure. Presence of 5V_ST would be an indication of a failure on the Main Board or possibly the Front PWB (IR) assembly. Suspect a possible short circuit loading the supply. Remember to observe the Front Power Indicating LED this may save some time. A lit LED indicates the Stand-By 5V voltage is present and the Microprocessor is communicating with the front LED driver IC.
The Main Board sends two commands to the Power Supply Board one being PWR the other is INV ON. These two signals are used to control the SMPS turn on sequence. First the command PWR (Pin 2) also known as POWER ON, activates the Ballast voltage 24V and the 24Vt and 12V lines to the Main board. The second command is INV ON (P201 pin 20). It is the Lamp Lighting Command Signal. If either command (PWR-ON or INV-ON) is missing it will result in a no picture symptom and the backlights will not turn on.
These voltages can easily be checked with the voltmeter. Remove AC Power, unplug the Connector to the Ballast P203. 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 the Main board. Check P700 or P201 pin 2 for the PWR-ON command (4.9V) to the Power Supply. Check P201 for 24V (Pins 17 or 18) and 12V (Pins 13 or 14). Confirm Pin 20 of P201 went to 4.8V. This is the INV ON signal needed to light the Lamps.

POWER SUPPLY PWB - LOW VOLTAGE CHECK

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 STBY5V on either pin 7, 8, 9 or 10 (5V).
If 5V Standby is not being generated, the SMPS PWB is defective and must be replaced. There is no need to continue with the next test.
Unplug P700 on the Main PWB and P203 to the Ballast.

TEST - 1

Add a 10K resistor between (5V STBY) pin 7, 8, 9 or 10 and Pin 2 (PWR). Apply AC. This will turn on the power supply.
Check that the 24V and 12V power supplies are turned on, P201 (24V pins 17 and 18) (12V pins 13 and 14) and 24V to the Ballast P203 Pins 1~5.
Remove AC power. Reinsert the plug P203 to the Ballast.

POWER SUPPLY PWB - BACKLIGHTS TEST

P700 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 another 10K resistor between (5V) pin 7, 8, 9 or 10 and Pin 20 (INV On).
Unplug the small ribbon connector CN1 (This floats P-DIM)
Apply AC Power. This simulates a Power On and Backlight On command.
Backlights Normal? If all is normal, the backlights should turn on.
Backlights Abnormal? Recheck connector P203 and confirm 24V on pins 1~5.
If low or missing, use diode mode to check the 24V line on Ballast connector CN1. If low, this indicates a shorted output FET).
If open, check the Ballast Fuse, possible Open.
Confirm the INV On/Off line P203 Pin 10 is going to 3V.
Confirm Pin 3 of CN1 has >2V.
If not, you will need to add 3V by adding a 10K resistor from 5V_ST to pin 3 of CN1. Backlights should light.