A guide on how to troubleshoot 2 seconds to black

[retiredcaps]

REVISION 0.1 - July 23, 2010

Revisions are sure to come. Make sure to read the latest posts for corrections or input from others.

I wrote this to help others by sharing what I have learned over the last 4 months. 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.

A guide on how to troubleshoot 2 seconds to black
==============================

Description of problem
==============

You turn on your LCD monitor and it displays an image of your screen and then suddenly it turns off after 1 or 2 seconds. The power LED stays on (or green) and you can still see the image by 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 board and logic board are working 100%. That leaves the inverter board to check.

Tools needed to troubleshoot
==================

You will need the following tools to troubleshoot:

a) a multimeter
b) camera to take clear focused pictures
c) solder iron to replace components with optional desolder wick or pump

Personality Traits required
================

a) ability to follow directions
b) some troubleshooting skills
c) determination
d) willingness to learn
e) patience

If you don't have at least one of the traits above, sell or give away your monitor to someone else. Seriously.

SAFETY
=====

Most of the tests below require a multimeter, but all the ones that I write about are with power off and unplugged. The CCFL test does not require a multimeter, but there is VERY HIGH VOLTAGE (600V to 1000V).

I take no responsibility 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 knowledgable for help.

Possible causes
=========

Here are some of the possible causes of "2 seconds to black" in no particular order. Your LCD monitor may have one or all the following.

1) Bad Capacitors
--------------------

Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bad in order to bad. They can be out
of tolerance uF (a 1000uF outputs 400uF) and high ESR (ohm). A multimeter will be insufficient to test for ESR. You need an ESR tester for test for ESR.

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

2) Shorted Transistors
-------------------------

On some brands (example: Benq) the transistors (C5707) are sometimes shorted. You can test for shorted transistors (with power off and unplugged)

a) put black probe (com) on pin 1 and red probe on pin 2 - read ohm
b) put black probe (com) on pin 1 and red probe on pin 3 - read ohm
c) put black probe (com) on pin 2 and red probe on pin 3 - read ohm

If any ohm reading is less than 20 ohm you have a shorted transistor and it will need to be replaced.

3) Open fuse
--------------

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

You can test for open fuses by (with power off and unplugged)

a) put black probe (com) on one pin and red probe on other pin - read ohm

If the reading is 0.3 or 0.4 ohm you have a good fuse. Anything higher 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.

4) Bad transformer
----------------------

The transformer converts the low voltage into high voltage to drive the ccfls. These can be bad. You can test for open windings on the transformer by (with power off and unplugged)

a) Number the pins on the transformers anyway you like
b) black probe on pin 1, red on pin 2 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

I'm guessing the secondaries should read 950 ohm (this will vary for different transformers). The primaries should read 1.3 ohm. Some will be 0L. If one secondary is 950ohm and the other is 750ohm, that would indicate a problem.

This test is not exhaustive as it does not detect all faults. For that, you will need a ring tester to test the coils.

5) Bad CCFL
--------------

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 connection or a variety of reasons. The easiest way to test for bad CCFLs is to have a least one other CCFL.

Let's assume that you have a LCD with 4 CCFLs (numbered 1 to 4) and a spare.

Pay ATTENTION as there is a VERY HIGH VOLTAGE (600V to 1000V)! 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.

6) Bad Diode
---------------

Diodes can be bad. To test a diode,

a) put your multimeter in diode test mode
b) put your black lead on one side and the red lead on the other - record reading
c) reverse the leads - recording reading

A good diode should read 0.4 to 0.7 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 as an "in circuit" test may not be conclusive.

7) Bad/cold/poor solder joints
----------------------------------

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

8) other bad components
-----------------------------

Voltage regulators, mosfets, other ICs, resistors can also be bad and need to measured to verify proper operation.

This section might get flushed out better as I run into more of these issues.

Misc suggestions
==========

1) Post clear focused pictures AFTER reading

https://www.badcaps.net/forum/showthread.php?t=1868

Take your boards to a window on a sunny day and use macro mode. Take a top down view of all your boards (front and back).

2) Use clear cohert language with grammar and punctuation. If you can't articulate your problem, no one can or will help you.

3) Make an effort and do some research before posting.

4) If you are new, please read the FAQs before posting. You are more likely to get help if you do.

5) Post MORE information that little. A post that says "MY MONITOR DOES NOT WORK. HLEP (sic) ME" is likely to be ignored. The more information you give, the better.

[Dgtech]

Re: A guide on how to troubleshoot 2 seconds to black

I have to run the "Personality Traits" checklist by the wife. I think i'm 5/5 but she may have other thoughts.

I'm glad you put this post up here. I will reference this in the future.

[newbie1]

Re: A guide on how to troubleshoot 2 seconds to black

Splendid guide.. i vote for it to be a 'sticky' thread!...

Kudos to retiredcaps, as well as all the veterans/masters here...

really helps me a lot in reviving a few (small number) of 'dead' LCD monitors..

[PlainBill]

Re: A guide on how to troubleshoot 2 seconds to black

It's a good start, and will help solve those monitors with bad CCFLs or wiring issues. A fault in the sense circuitry is much more involved.

As I commented in another thread, it is very rare that an open fuse or a shorted transistor would result in a 'two seconds to black' issue. With an open fuse you wouldn't get any backlights; with a shorted transistor at best you might get a fraction of a second flash.

PlainBill

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

A fault in the sense circuitry is much more involved.

Agreed. I don't have the experience or knowledge yet in that area. I am following all those sense circuitry threads, but can't contribute anything yet.

As I commented in another thread, it is very rare that an open fuse or a shorted transistor would result in a 'two seconds to black' issue. With an open fuse you wouldn't get any backlights; with a shorted transistor at best you might get a fraction of a second flash.

PlainBill

For those wondering what thread, here is why I included the fuse part.

I totally agree about an open fuse would cause zero second to black.

The only reason I mention is that I have a "in repair process" NEC 1700V monitor and I read this part from

http://www.electronicspoint.com/nec...tor-t75165.html

">>I checked those two fuses on the inverter
>>board, AOK. I don't think the screen
>>would even light at all
>> if those fuses were bad.

> Yes, it will if only one of them is bad. I've
> fixed several of these with that fault."

I can make revision 0.2 once I get more feedback and most importantly corrections.

[Per Hansson]

Re: A guide on how to troubleshoot 2 seconds to black

Very good post, I vote for sticky too!
I will reference this when I need it next time
Thank you so much!

[paule22]

Re: A guide on how to troubleshoot 2 seconds to black

many thanks for posting this great guide much appreciated

[CompSol]

Re: A guide on how to troubleshoot 2 seconds to black

I`ve been experiencing that these days, however, I`d like to ask, if all that above does apply in a case when monitor turns on eventually and then runs as nothing is happening? In my case, I get the black screen after 2-3 seconds, but then if I try to turn the monitor off and on several times, eventually it turns on and works properly. It takes about 20 minutes turning it off and on, sometimes longer, today it took much longer, but the monitor turned on finally and runs. Once I turn the monitor off, I`m in the "2 seconds to black" issue again.
Should I look for another possible cause to the problem in addition to the ones listed above?

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

In my case, I get the black screen after 2-3 seconds, but then if I try to turn the monitor off and on several times, eventually it turns on and works properly. It takes about 20 minutes turning it off and on, sometimes longer, today it took much longer, but the monitor turned on finally and runs.

Start a new thread with your problem and the make/model of the monitor. What you are describing is a classic sign of bad caps.

If you take your monitor apart, you will probably find obviously bad caps.

[alexanna]

Re: A guide on how to troubleshoot 2 seconds to black

Retiredcaps what would be the best way to add some suggestions to your thread. Once they are posted here it’s like writing them in stone. I just want to make sure you agree with them.
Al.

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

Retiredcaps what would be the best way to add some suggestions to your thread. Once they are posted here it's like writing them in stone. I just want to make sure you agree with them.
Al.

Good timing on your question.

I have been making changes for 0.2 in the last 48 hours so any feedback would be appreciated.

There are a lot of corrections as I have learned more in the last 45 days since revision 0.1.

I'll send you or anyone else who wants a copy of 0.2 (PM me). I have thick skin. Don't hold back on the comments.

I'm hoping to post 0.2 in the next week or so.

[alexanna]

Re: A guide on how to troubleshoot 2 seconds to black

I will read over the Pm, it will be later this evening.
Thanks Al.

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

UPDATED and REVISED - PART 1

REVISION 0.2 - Nov 3, 2010

More revisions are sure to come. Make sure to read the latest posts for corrections or input from others.

I wrote this to help others by sharing what I have learned over the last 6 months. 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.

A guide on how to troubleshoot 2 seconds to black
==============================

Description of problem
==============

You turn on your LCD monitor and it displays a computer image of your screen and then suddenly it turns off after 1 or 2 seconds. The power LED stays on (or green) and you can still see the computer image by 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 board and logic board are working 100%. That leaves the inverter section to check.

Tools needed to troubleshoot
==================

You will need the following tools to troubleshoot:

a) multimeter
b) camera to take clear focused pictures
c) solder iron to replace components with optional desolder wick or pump

Personality Traits required
================

a) ability to follow directions
b) some troubleshooting skills
c) determination
d) willingness to learn
e) patience

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
=====

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

I take no responsibility 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 ranging multimeter, set it to 200 (two hundred) ohms. Touch the black and red probe together. It should read 0.3 or 0.4 ohms. If it is higher than 1.0 ohm, there is something wrong with your multimeter.

If your multimeter reads "1" or "OL", it means the measurement is outside your chosen range. Don't confuse "1" on the left hand side of this display with 1.0 on the right hand side. The first means out of range and the second means 1.0 unit of your measurement.

Do NOT use the continuity or "beep" feature of your multimeter for measurements. Some multimeters "beep good" for resistance readings less than 1.5k ohms.

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

Possible causes
=========

Here are some of the possible causes of "2 seconds to black" in no particular order. 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 (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, and United Chemicon are suggested. A list of recommended caps can be found at

https://www.badcaps.net/forum/showthread.php?t=2280

PCBONEZ talks about how to choose the right series at

https://www.badcaps.net/forum/showpo...47&postcount=3

2) Shorted Transistors/MOSFETs
------------------------------------

On some LCD brands (example: Benq) the transistors (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 ohm reading is less than 30 ohm 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). You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any ohm reading is less than 30 ohm you might have shorted mosfet. Remove from circuit and repeat the tests 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 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

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.

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=8598

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 fuses "in circuit" by (with power off and unplugged)

a) put black probe on one pin and red probe on other pin - read/record ohm

A reading of less than 1.0 ohms indicates a good fuse. Anything higher than 1.0 ohm 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 inverter boards have 2 fuses. One fuse could be bad and one could be good which results in 2 seconds to black. In newer 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).

continued in Part 2 below ...

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

Part 2

4) Bad transformer
----------------------

The transformer (T designation) converts the low voltage into high voltage to drive the ccfls. These can be bad.

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 by (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 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

I'm guessing the secondaries should read 950 ohm (this will vary for different transformers). If one secondary is 950ohm and the other is 750ohm, that would indicate a problem. A 4% variation or more in the secondaries suggests a bad transformer.

This test is not exhaustive as it does not detect all faults. For that, you will need a ring tester to test the coils.

Here is a youtube video showing the process on how to measure secondaries

http://www.youtube.com/watch?v=eNuGWBPRGKA

or if you have a ring tester, see this video

http://www.youtube.com/watch?v=HMUazhb0bhc

5) Bad CCFL
--------------

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 other good CCFL. If you see a pinkish/redish 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.

Pay ATTENTION as there is a VERY HIGH VOLTAGE (600V to 1000V)! 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.

Here are pictures of some bad CCFLs

https://www.badcaps.net/forum/showthread.php?t=10078

https://www.badcaps.net/forum/showthread.php?t=8978

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. Here is a link to photos of good and bad solder joints.

http://workmanship.nasa.gov/lib/insp...uirements.html

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 a 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 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any ohm reading is less than 30 ohm 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 resisiors 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 not the same, you will have to remove the resistor and test it out of circuit to verify.

http://en.wikipedia.org/wiki/Resistor#Resistor_marking

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 lead on one side and the red lead on the other - record reading
c) reverse the leads - recording 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 -> 2 seconds to black.

PlainBill describes 2 seconds to black best in these posts ...

https://www.badcaps.net/forum/showpo...5&postcount=25

https://www.badcaps.net/forum/showpo...10&postcount=4

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 (see section 7). Or the inverter IC itself might be bad.

Misc suggestions
==========

1) Post clear focused pictures AFTER reading

https://www.badcaps.net/forum/showthread.php?t=1868

Please do not post pictures inline as they slow down the loading of pages.

For best picture quality and clarity take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focused pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

Here is an example of the pictures we want.

https://www.badcaps.net/forum/showpo...94&postcount=1

2) Use clear coherent language with grammar and punctuation. If you can't articulate your problem, no one can or will help you.

3) Make an effort and do some research before posting.

4) If you are new, please read the FAQs before posting. You are more likely to get help if you do.

5) Post MORE information that little. A post that says "MY MONITOR DOES NOT WORK. HLEP (sic) ME" is likely to be ignored. The more information you give, the better.

Changes in revision 0.2
==============

1) added "case studies"
2) added youtube videos
3) added info on how to test mosfets, voltage regulators, resistors
4) added info how a sense circuit works with inverter IC
5) added instructions for manual multimeter
6) added info about testing "in circuit"
7) added info about using continuity setting on multimeter
8) added info about pinkish/redish hue on ccfl
9) fixed up some obvious typos, spelling and grammar
10) added section on multimeter
11) added board PCB designations
12) forum member pedro suggested that I change the good fuse reading to suggest a range rather than a "hard" value of 0.3 ohms

[billy66]

Re: A guide on how to troubleshoot 2 seconds to black

Excellent update! I've been putting together a troubleshooting guide notebook for me to refer to often... I'll be printing this out and using it often. THANKS!

[flightengineer]

Re: A guide on how to troubleshoot 2 seconds to black

Hi all.. it was very helpful steps .
at least for me and i`m thankful to you.

[jgmanza]

Re: A guide on how to troubleshoot 2 seconds to black

Thanks. This is very useful, thanks.

[DTLMG]

Re: A guide on how to troubleshoot 2 seconds to black

Didnt I read there were some youtube videos somewhere? Im interested in learning how to do the voltage readings on the PSU. I am a visual person as I am older.

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

REVISION 0.3 - Dec 16, 2011

More revisions are sure to come. Make sure to read the latest posts for corrections or input from others.

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.

A guide on how to troubleshoot 2 seconds to black

Description of problem

You turn on your LCD monitor and it displays a computer image on your screen and then suddenly it turns off after 1 or 2 seconds. The power LED stays on (or green) and you can/may still see the computer image by 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 and logic board are working properly.

Tools needed to troubleshoot

You will need the following tools to troubleshoot:

a) multimeter
b) camera to take 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

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 tests do not require a multimeter, but there is VERY HIGH VOLTAGE (600V to 1000V).

I take no responsibility 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 ohm, 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 on the right hand side. The first means out of range and the second means 1.0 unit of your 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 measurements 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 (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester 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 United Chemicon are suggested. A list of recommended caps can be found at

https://www.badcaps.net/forum/showthread.php?t=2280

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

Here is an example of how to choose capacitors with respect to capacitance, voltage, diameter, height, ripple and ESR.

https://www.badcaps.net/forum/showpo...4&postcount=19

2) Shorted Transistors/MOSFETs

On some LCD brands (example: Benq) the transistors (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 pin ICs only. You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeat the tests 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 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

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.

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=17659

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 fuses "in circuit" by (with power off and unplugged)

a) put black probe on one pin and red probe on other pin - read/record ohm

A reading of less than 1.0 ohms indicates a good fuse. Anything higher than 1.0 ohm 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 inverter 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).

Here is a case study.

https://www.badcaps.net/forum/showthread.php?p=197027

[retiredcaps]

Re: A guide on how to troubleshoot 2 seconds to black

Part 2

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 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - 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.

This test is not exhaustive as it does not detect all faults.

Here is an example of what to measure.

http://lcdparts.net/TransformerDetai...ProductID=2724

Here is a case study.

https://www.badcaps.net/forum/showthread.php?t=12121


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/redish 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.

Pay ATTENTION as there is a VERY HIGH VOLTAGE (600V to 1000V)! 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.

Here are pictures of some bad CCFLs

https://www.badcaps.net/forum/showthread.php?t=10078

https://www.badcaps.net/forum/showthread.php?t=8978

b) Alternatively, if you do not have a spare CCFL, then try this test.

a) TURN POWER OFF and unplug the monitor and wait 1 minute
b) disconnect all CCFLs expect #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) disconnect all CCFLs expect #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) disconnect all CCFLs expect #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) disconnect all CCFLs expect #4
l) 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 that 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.

PlainBill describes the procedure if they are in pairs at

https://www.badcaps.net/forum/showpo...&postcount=297

c) Sometimes the CCFLs are fine, but the wiring has degraded and makes intermittent contact with the CCFL. Some examples can be found at

http://s807.photobucket.com/albums/y...klight%20lamp/

https://www.badcaps.net/forum/showpo...5&postcount=18

https://www.badcaps.net/forum/showpo...6&postcount=44

d) Replacing a CCFL is a delicate 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. Here is a link to photos of good and bad solder joints.

http://workmanship.nasa.gov/lib/insp...uirements.html

Here is an example of a bad solder joint causing 2 seconds to black.

https://www.badcaps.net/forum/showthread.php?t=12134

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 a 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 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

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 resisiors 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 not the same, you will have to remove the resistor and test it out of circuit to verify.

http://en.wikipedia.org/wiki/Electronic_color_code

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 lead on one side and the red lead on the other - record reading
c) reverse the leads - recording 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 -> 2 seconds to black.

PlainBill describes 2 seconds to black best in these posts ...

https://www.badcaps.net/forum/showpo...5&postcount=25

https://www.badcaps.net/forum/showpo...10&postcount=4

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 (see section 7). Or the inverter IC itself might be bad.