Hari ini, saya akan menyajikan cara melakukan analisa kerusakan pada Monitor LCD atau TV. Sesuai judulnya mungkin ada yang masih tidak mengerti dengan pengertian “2 seconds to black”. Jika kita artikan, kira – kira pengertiannya adalah “2 detik menjadi hitam/gelap”.

Timbul pertanyaan lagi, apa maksudnya konteks “hitam/gelap” dalam kaitannya dengan kerusakan Monitor LCD atau TV?

Yang dimaksud dengan “hitam/ gelap” disini dapat kita artikan kira – kira sebagai berikut menurut deskripsi si penulis yaitu retiredcaps.

“Anda menghidupkan Monitor LCD atau TV dan terdapat tampilan atau gambar di layar, dan kemudian secara tiba – tiba tampilan di layar menjadi hitam/gelap setelah 1 atau 2 detik. Lampu indikator masih tetap menyala (hijau) dan ketika layar LCD disinari dengan lampu flash atau senter, kita dapat melihat secara seksama dari dekat bahwa ada tampilan atau gambar di layar. Inilah yang disebut “2 detik menjadi hitam/gelap”

Nah, saya tidak akan memaparkan lebih jauh lagi karena sudah cukup jelas pemaparan saya. Silakan baca pemaparan lengkap di bawah ini, jika anda mengalami kesulitan dalam mengartikannya, gunakan translator di samping kanan blog ini. Selamat membaca dan saya harap artikel ini berguna dalam melakukan troubleshooting Monitor LCD atau TV.

I wrote this to help others by sharing what I have learned. This information is nothing new, but it is scattered all over different threads.

This is not a definitive guide as others have far greater knowledge and experience.


DESCRIPTION OF PROBLEM


You turn on your LCD Monitor or TV and it displays an image on your screen and then suddenly it turns off after 1 or 2 seconds. The power LED indicator stays on (or green) and you can/may still see the computer image shining a flashlight on it. This is called “2 seconds to black”.

WHERE THE PROBLEM LIES

Since you are seeing the image, but with no backlight, we will assume for now that the power supply and logic/main board are working properly.

TOOLS NEEDED TO TROUBLESHOOT

You will need the following tools to troubleshoot:

a.       Multimeter (analog or digital)

b.       Camera to take a clear focused pictures

c.       Solder iron to replace components

PERSONALITY TRAITS REQUIRED

a.       Ability to follow directions

b.       Troubleshooting skills

c.       Determination

d.       Willingness to learn

e.       Patience

f.        Ability to articulate your problem clearly

If you don’t have at least one of the traits above, sell or give away your monitor to someone else. Seriously. Don’t dump in the garbage. Recycle it properly please.

SAFETY PRECAUTIONS

Most of the tests below require a multimeter, but all the procedures that I write about are with power off and LCD unplugged. The CCFL (Cold Cathode Fluorescent Lamps) tests do not require a multimeter, but there is VERY HIGH VOLTAGE (600V to 1000V).

I take no responsbility for any of the tests below that may cause you or your monitor any harm. If you are not comfortable, do not try it. Ask someone knowledgeable for help.

MULTIMETER

If you have a manual range multimeter, set it to 200 (two hundred) ohms. Touch the black and red probe together. It should read between 0.1 or 0.5 ohms. If it is higher than 1.0 ohms, there is something likely wrong with your multimeter. Either the test leads are frayed internally and/or the battery is dying which will result inaccurate readings.

If your multimeter reads “1” or “0L’, it means the measurement is outside your chosen range. Don’t confuse “1” on the left hand side of this display with 1.0 ohms on the right hand side. The first means out of range and the second means 1.0 unit of measurement.

Do not use the continuity or “beep” feature of your multimeter for measurements. Some multimeters “beep continuous” for resistance readings less than 1.5k ohms.

Always post the actual results of your measurement when asking for help.

POSSIBLE CAUSES

Here are some of the possible causes of “2 seconds to black”. Your LCD monitor may have one or all the following. I suggest reading all the possible causes and then applying the ones that make the most sense to your situation.

1.    Bad capacitors
Capacitors (C designation on the PCB board) die from age, heat, and shoddy build quality.

Capacitors do not have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohms). A multimeter will be insufficient to test for ESR. For that you need an ESR Tester/Meter which costs between $50 and $300.

Bad capacitors will not provide stable reliable power which may cause “2 seconds to black”.

Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, Nichicon, and UCC (United Chemicon) are suggested.

The one exception might be the largest capacitor on the power board which rarely, but not never, fails.

2.    Shorted Transistor/MOSFETs

On some LCD brands (example: BenQ) the transistor (C5707) are sometimes shorted. Transistors are usually marked with a “Q” designation/

       If you have a manual range multimeter, set it to 200 ohms (two hundred). You can test for shorted transistors “in circuit” (with power off and unplugged)

a.       Put black probe on pin 1 and red probe on pin 2 – read/record ohm

b.       Put black probe on pin 1 and red probe on pin 3 – read/record ohm

c.       Put black probe on pin 2 and red probe on pin 3 – read/record ohm

If any reading is less than 30 ohms you might have shorted transistor. Remove the transistor and repeat the tests out of circuit to verify.

Note : a shorted transistor would likely cause a very brief flash of the backlight or no backlight.

Mosfets

If you have a manual range multimeter, set it to 200 ohms (two hundred). This is for 3 pins ICs only. You can test a mosfet (Q, IC designation) “in circuit” (with power off and unplugged)

a.       Black probe on pin 1, red on pin 2 – read/record ohm

b.       Black probe on pin 1, red on pin 3 – read/record ohm

c.       Black probe on pin 2, red on pin 3 – read/record ohm

If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeats the test to verify.

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a.       Black on pin S1, red on pin G1 - read/record ohm

b.       Black on pin S1, red on pin D1 - read/record ohm

c.       Black on pin G1, red on pin D1 - read/record ohm

Repeat for the “2” pins. That is S2-G2, S2-D2, G2-D2.

Note : a shorted mosfet would likely cause a very brief flash of the backlight or no backlight.

3.    Open fuse

Some boards will have a fuse (F designation) or picofuse (PF designation) and they may be open because a transistor was shorted or some other component went bad.

If you have a manual range multimeter, set it to 200 ohms (two hundred). You can test for open fuse “in circuit” (with power off and unplugged)

a.       Put black probe on one pin and red probe on other pin - read/record ohms

A reading of less than 1.0 ohms indicates a good fuse. Anything higher than 1.0 ohms is a sign of an open fuse. Do not replace fuses and turn on the power back on without checking for what caused the fuse to go open otherwise you will just be replacing the fuse again.

Note : in older monitors, some inverters boards have 2 fuses. One fuse could be bad and one could be good which results in 2 seconds to black. In newer LCD monitors, there is usually only one fuse protecting the inverter section. If that fuse is bad, you would get no backlight flash (i.e. no 2 seconds to black)

                                                                                                                

4.    Bad inverter transformer

The transformer (T designation) converts the low voltage into high voltage to drive the CCFLs.

These can be bad. A simple test is to measure the resistance of the secondary windings. If you look at the transformer, these will be the thinner guage windings/wires. Sometimes you can tell which are the secondary inverter transformer pins. If you cannot, then you have to use “brute force” and measure all possible combinations as explained below.

If you have a manual range multimeter, set it to 2k ohms (two thousand). You can test for open windings “in circuit” on the transformer (with power off and unplugged).

Power off and unplug monitor. WAIT 5 MINUTES BEFORE STARTING the ohms measurements. Waiting allows the capacitors and other components to discharge.

a.         Number the pins on the transformers anyway you like

b.         Black probe on pin 1, red on pin 2 – read/record ohm

c.         Black probe on pin 1, red on pin 3 – read/record ohm

d.         Black probe on pin 1, red on pin 4 – read/record ohm

e.         etc

f.          Black probe on pin 1, red on pin last – read/record ohm

g.         Black probe on pin 2, red on pin 3 – read/record ohm

h.         Black probe on pin 2, red on pin 4 – read/record ohm

i.           Etc

j.           Black probe on pin 2, red on pin last – read/record ohm

k.         Black probe on pin 3, red on pin 4 – read/record ohm

l.           Etc

m.       Finally, black probe on pin last 1, red on pin last –read/record ohm

A 3% variation or more in the secondaries suggests a bad transformer. For example, if one reading is 950 ohms and the other is 750 ohms, then one of the transformers is bad.

5.    Bad CCFL/Wiring

a.       Pay attention as there is a VERY HIGH VOLTAGE (600v to 1000V)! no multimeter is required for this test.

The CCFLs light up the panel and they can be bad due to age, bad solder, bad wiring connection or a variety of reasons. The easiest way to test for bad CCFLs is to have a least one good CCFL. If you see a pinkish/reddish hue, this is a sign that your CCFLs are dying.

Let’s assume that you have a LCD with 4 CCFLs (numbered 1 to 4) and a good spare. We are trying to narrow down which CCFL is bad by substituting in a good one.

As a safety precaution, it might help to have someone around when you are doing this if something screws up.

a.       TURN POWER OFF and unplug the monitor and wait 1 minute

b.       Disconnect CCFL #1 and plug in spare CCFL into spot #1

c.       Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

d.       TURN POWER OFF and unplug the monitor and wait 1 minute

e.       Reconnect CCFL #1 and disconnect CCFL #2 and plug in spare CCFL into spot #2

f.        Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

g.       TURN POWER OFF and unplug the monitor and wait 1 minute

h.       Reconnect CCFL #2 and disconnect CCFL #3 and plug in spare CCFL into spot #3

i.         Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

j.         TURN POWER OFF and unplug the monitor and wait 1 minute

k.       Reconnect CCFL #3 and disconnect CCFL #4 and plug in spare CCFL into spot #4

l.         Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

If you have a bad CCFL, one of the tests above should show you which one. If you still have “2 seconds to black”, then we can assume it is not due to a bad CCFL.

b.        Alternatively, if you don’t have a spare CCFL, the try this test

1.       TURN POWER OFF and unplug the monitor and wait 1 minute

2.       Disconnect all CCFLs except #1

3.       Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

4.       TURN POWER OFF and unplug the monitor and wait 1 minute

5.       Disconnect all CCFLs except #2

6.       Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

7.       TURN POWER OFF and unplug the monitor and wait 1 minute

8.       Disconnect all CCFLs except #3

9.       Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

10.   TURN POWER OFF and unplug the monitor and wait 1 minute

11.   Disconnect all CCFLs except #4

12.   Plug in monitor and turn monitor on – note if “2 seconds to black” occurs

If one of the CCFLs does not light up, it is likely physically damaged (cracked) or the wiring is completely broken to it. Take out the CCFL and inspect it. If all 4 CCFLs do show “2 seconds to black”, one or more can still be bad. This test only discovers a completely dead CCFL or completely broken wiring.

c.       Sometimes the CCFLs are fine, but the wiring has degraded and makes intermittent contact with the CCFL.

d.      Replacing the CCFL is a dedicate operation. See “Lamp Soldering Tutorial” at http://ccflwarehouse.com/lasotu.html to see what steps are involved. CCFLs can be sold “bare” or “pre-harnessed”. The latter is easier to replace and install, but is more expensive.

6.      Bad/cold/poor solder joints

Inspect the backside of the board carefully with a microscope or magnifying glass and look for bad solder joints.

7.      Other bad components

These components are less likely to cause 2 seconds to black, but I have included them just in case.

7.1   Voltage regulators

Voltage regulators (U designation) can be bad. They can be shorted or output the incorrect voltage. The test described below only tests the former.

If you have manual range multimeter, set it to 200 ohms (two hundred). You can test voltage regulators “in circuit” for shorts by (power off and unplugged)

a.       Black on pin 1, red on pin 2 – read/record ohm

b.       Black on pin 1, red on pin 3 – read/record ohm

c.       Black on pin 2, red on pin 3 – read/record ohm

If any reading is less than 30 ohms you might have shorted voltage regulator. Remove from circuit and repeat the tests to verify.

7.2   Resistors

Resistors (R designation) can be blown or become open.

You can test resistor “in circuit by (power off and unplugged)

a.       Put black probe (com) on one pin and red probe on other pin – read/record ohm

Compare the ohms reading with the color code or marking on the resistor. If the value is higher than marking on resistor, or show 0 ohms reading, you will have to remove the resistor and test it out of circuit to verify. You don’t need to do this if the resistor measured a lower than marking code of resistor because it looks like the resistor is paralled with other components.

7.3   Bad diode

Diodes (D or ZD designation) can be bad. To test a diode in circuit,

a.       Put your multimeter in diode test mode

b.       Put your black probe on one side and the red probe on the other – record reading

c.       Reverse the probe leads – record reading

A good diode should read 0.4v to 0.7v in one direction and 0L in the other. If you get a reading in both directions, you will have to desolder one leg and retest to verify.

8.      Inverter IC sense circuitry/feedback

This is probably the hardest to describe and hardest to troubleshoot. If you are at this stage, you do need a basic knowledge of how to use a multimeter, some electronics knowledge, and decent troubleshooting skills.

One of the inverter IC’s function is to monitor the environment. If something “goes wrong” or falls outside the specified operating range, the IC shuts down the backlights to protect them a 2 seconds to black.

The standard procedure to identify inverter IC, find its datasheet, and look at its “typical application” diagram. The next step is to measure the voltages on each of the inverter IC pins and compare them to the specified datasheet. If any value is outside the specified operating range, then we have to determine what component or components is causing that.

The components that are part of the sense circuitry might include diodes, resistors, and capacitors. Or the inverter IC itself might be bad.

Note : Please contact trained service technician if you don’t know how to handle high voltage section on Monitor or TV, I will take no responsible if you got electrocuted. I have no credit at all for this guide, it all belong to retiredcaps, I just wanna share the useful guide for troubleshooting job on your LCD Monitor or TV. Thank you for such a great guide.



Links : Badcaps Forum

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