Checking the inverter board and CCFL lamp for a HP ProBook 4530sNotebook PC running Windows 7 Profes

[t]

Some days when the laptop is turned on, the user sees only a blank
screen. But, the notebook starts up fine as connecting it to an
external monitor shows the different accounts on the notebook. The user
can log-in to the account and use it. Other days, the
notebook monitor works properly and everything shows up properly and
user can use it without issues. I estimate something is malfunctioning
with the inverter board for the LCD or the CCFL lamp on some days. There
was no diagnostic tools which came with the laptop
to check those parts.

1. How can I check if the inverter board for the LCD or the CCFL lamp
are working fine or not?

2. Is there a software utility I can use to check them(inverter board or
CCFL lamp) before I open the LCD?

3. Can something else be causing the issue?

I notice
http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp/
and
http://www.ccfldirect.com/lcdtutorial.html explain how to replace the
lamp. However, I want to find out which
is faulty(lamp or the inverter board)

The laptop was purchased in Oct 2011.

Any suggestions would be appreciated.

Thanks

 

[Paul]

Some days when the laptop is turned on, the user sees only a blank
screen. But, the notebook starts up fine as connecting it to an
external monitor shows the different accounts on the notebook. The user
can log-in to the account and use it. Other days, the
notebook monitor works properly and everything shows up properly and
user can use it without issues. I estimate something is malfunctioning
with the inverter board for the LCD or the CCFL lamp on some days. There
was no diagnostic tools which came with the laptop
to check those parts.

1. How can I check if the inverter board for the LCD or the CCFL lamp
are working fine or not?

2. Is there a software utility I can use to check them(inverter board or
CCFL lamp) before I open the LCD?

3. Can something else be causing the issue?

I notice
http://www.laptoprepair101.com/laptop/2007/12/09/replace-laptop-backlight-ccfl-lamp/
and
http://www.ccfldirect.com/lcdtutorial.html explain how to replace the
lamp. However, I want to find out which
is faulty(lamp or the inverter board)

The laptop was purchased in Oct 2011.

Any suggestions would be appreciated.

Thanks

A quick Google, says it has a LED backlight. High voltage
inverter and CCFL tubes are not involved.

So your repair strategy is going to be quite different.

I've not seen any info, on how LED backlights are controlled.
In theory, they'll be PWM (pulse width modulation of a constant
current source). That prevents color shift, as you vary the LED
intensity. But I don't know if they bother to modulate
the LEDs individually when the panel is in movie mode or the like.
In any case, flaky inverter boards should not be involved. The
laptop battery contains enough voltage to run a LED, without an inverter.
But they're free to do anything they want (no matter how crazy).
And I can't guess how crazy these people are.

If the PWM structure is relatively simple, it could either be
a control signal failure, or the PWM has failed for some reason.
The PWM could be as simple as a single power transistor.

*******

Another thing to consider, is the F5 screen toggle. Perhaps the
stupid thing is starting with the external monitor enabled, and
if the user tries the F5 thing, maybe the screen will come back.
It might even be, that the software attempts to probe the panel,
and thinks (for whatever reason), the panel is not present.
That makes more sense, than a PWM failure.

That unit is also dual-GPU. The Intel GPU in the chipset is used,
to save power. The ATI GPU is used, when the user plays a 3D game,
and better 3D performance is required. And that means, there are
also the two GPUs involved, in terms of deciding there is an
LCD panel present. I.e. Lots of possibilities for software
to screw up.

Paul

 

[t]

A quick Google, says it has a LED backlight. High voltage
inverter and CCFL tubes are not involved.

Thanks, so does the LED backlight use a regular inverter instead of high
voltage inverter?

That unit is also dual-GPU. The Intel GPU in the chipset is used,
to save power. The ATI GPU is used, when the user plays a 3D game,
and better 3D performance is required. And that means, there are
also the two GPUs involved, in terms of deciding there is an
LCD panel present. I.e. Lots of possibilities for software
to screw up.

How do the dual GPUs matter here? I estimate it starts with the Intel
GPU and when it detects intense graphical work(like game playing), it
would switch from ATI GPU. Or, do these models have a different way of
choosing which GPU to use?

Are there any signs of faulty connection I need to look out for? There
is no flickering and I know flickering means the backlight is going to
malfunction for a CCFL lamp.

Thanks for your advice and time.

 

[Paul]

Thanks, so does the LED backlight use a regular inverter instead of high
voltage inverter?




How do the dual GPUs matter here? I estimate it starts with the Intel
GPU and when it detects intense graphical work(like game playing), it
would switch from ATI GPU. Or, do these models have a different way of
choosing which GPU to use?

Are there any signs of faulty connection I need to look out for? There
is no flickering and I know flickering means the backlight is going to
malfunction for a CCFL lamp.

Thanks for your advice and time.

There won't be an inverter, in the same sense as the 1000VAC one used
for CCFLs. There are still power circuits, but their design is
different (and likely, more reliable than an inverter).

There is not even a need for it to flicker. Since LEDs have
no "ignite" or "burn" phase, no plasma or gases, there is nothing
to flicker. Only a cold solder joint would flicker, and since the
panel actually has four LED chains, only a quarter of the
panel would flicker, if the solder joint on one LED was bad.

You can start with Ebay, if regular diagnostic sites aren't helping.
Here, I see a picture of the panel. Jackpot! Got a part number.

http://www.ebay.com/itm/GENUINE-SAM...Laptop_Screens_LCD_Panels&hash=item4ac5db370f

LTN156AT05

That gets me a hit here.

http://www.samsung.com/us/business/oem-solutions/pdfs/PSG2011_web.pdf

Of course, the Samsung site is a waste of time.

I found a datasheet for something close (glare finish rather than matte), here.
So this should be pretty close.

http://lcd-screen.com.ua/data/pdf/1168.pdf

LTN156AT05 is a color active matrix TFT
15.6"
1366 x 768 pixels
display up to 262,144 colors [means 6 bit dithered, 64*64*64 colors]

LED Back Light with embedded LED Driver

The panel electronics (like, the LVDS interface) runs at 3.3V.

The LED supply is listed as 6V to 20V. That is boosted enough,
to drive eleven LEDs in series (3.2V x 11 = 35.2V). So a switching
power supply of some sort, converts VBL+ into a 35.2V source. The
LED string runs at 20mA. Probably a 20mA current source, intended to handle
a compliance voltage of 35 to 37 volts (as listed on page 12).

3.3V ---> Run LVDS interface
6-20V ---> Powers LED power supply ---> 35.2V, PWM modulated at LED string

Another page is hinting, the LEDs are arranged in four channels.
Implying a total of 44 LEDs. 35.2V * 0.02mA = 0.7W or about 50 lumens
(estimated) per chain. Roughly the equivalent of a 20W lightbulb, in
terms of total light output from 44 LEDS.

The PWM control signal on the cable, is a 5V logic level. It is
intended to operate between 200Hz and 1000Hz (above flicker perception
range). The control range is listed as 10% to 100%, meaning PWM doesn't
go to zero on its own. There is also an Enable signal.

The pinout is on page 14.

PWM control is on pin 35.
Enable control is on pin 36.

To light the panel, Pin 36 must have a voltage
above 2.0V on it. A logic low (<0.5V), turns off the
backlight completely.

With Pin 36 logic high, the PWM Pin 35 control takes over.
The PWM must also be logic high. And the percentage
of the time the 200Hz signal is high, determines the
intensity of the LEDs. For example, if it did this, the
backlight would run at about 70% or so. As the signal
is high, 70% of the time.

2.0V +----+ +----+ +----+ ~200Hz

| | | | |
<0.5 -+ +-+ +-+

Page 20 of the data sheet, covers sequencing. You're supposed
to apply panel power (3.3V) before LED power (6-20V). And
the pin 36 Enable is used to gate the PWM for some reason.
They mumble something about latchup (panel stops working),
if the sequence is not obeyed. From one perspective, there's
no reason for the LED supply, to have anything to do with
the LVDS end. It implies that perhaps, the same boosted ~35V
internal supply, might also be used to run the LCD panel
horizontal and vertical driver chips.

In any case, you have a delightfully contradictory document
to work with. (I.e. Page 25 warns of "fluorescent lamp", when
the stupid panel is LED based. Hahaha. Copy-paste-twits)
Yes, there is a slight shock hazard, as the LED chain runs
at 35V, so don't run your bathwater, and reach out and touch it
Who knows, the actual LCD panel driver pins, may have more
voltage than that, but they're not required to tell you
about those. As they're not an "interface" issue. Purely
an internal design issue.

You can see in the Ebay photo, there are places to probe with
your multimeter, if you're bored.

Have fun,
Paul

 

[VanguardLH]

Some days when the laptop is turned on, the user sees only a blank
screen. But, the notebook starts up fine as connecting it to an
external monitor shows the different accounts on the notebook. The user
can log-in to the account and use it. Other days, the
notebook monitor works properly and everything shows up properly and
user can use it without issues.
...
3. Can something else be causing the issue?

Could be a problem in switching to/from laptop/dual/external monitor
modes. The laptop has its own monitor mode, obviously. Another is to
show the display on both the laptop monitor and the external monitor
(which shares the same resolution and probably means lower on the
external monitor). Another might be to only show the display on the
external monitor (since it probably has higher resolution). Hitting
the Fn and the monitor key rotates between the monitor modes. Make
sure during testing of the laptop monitor that the laptop is
configured to only use its own monitor.

Have YOU seen the symptom? Or has just the user told you about them?
If you haven't seen them and the user only told you about them then
maybe the user is accidentally pressing the wrong keys and has been
toggling the display mode.

 

[t]

Thanks, so does the LED backlight use a regular inverter instead of
high voltage inverter?




How do the dual GPUs matter here? I estimate it starts with the Intel
GPU and when it detects intense graphical work(like game playing), it
would switch from ATI GPU. Or, do these models have a different way of
choosing which GPU to use?

Are there any signs of faulty connection I need to look out for? There
is no flickering and I know flickering means the backlight is going to
malfunction for a CCFL lamp.

Thanks for your advice and time.

There won't be an inverter, in the same sense as the 1000VAC one used
for CCFLs. There are still power circuits, but their design is
different (and likely, more reliable than an inverter).

There is not even a need for it to flicker. Since LEDs have
no "ignite" or "burn" phase, no plasma or gases, there is nothing
to flicker. Only a cold solder joint would flicker, and since the
panel actually has four LED chains, only a quarter of the
panel would flicker, if the solder joint on one LED was bad.

You can start with Ebay, if regular diagnostic sites aren't helping.
Here, I see a picture of the panel. Jackpot! Got a part number.

http://www.ebay.com/itm/GENUINE-SAM...Laptop_Screens_LCD_Panels&hash=item4ac5db370f


LTN156AT05

That gets me a hit here.

http://www.samsung.com/us/business/oem-solutions/pdfs/PSG2011_web.pdf

Of course, the Samsung site is a waste of time.

I found a datasheet for something close (glare finish rather than
matte), here.
So this should be pretty close.

http://lcd-screen.com.ua/data/pdf/1168.pdf

LTN156AT05 is a color active matrix TFT
15.6"
1366 x 768 pixels
display up to 262,144 colors [means 6 bit dithered, 64*64*64 colors]

LED Back Light with embedded LED Driver

The panel electronics (like, the LVDS interface) runs at 3.3V.

The LED supply is listed as 6V to 20V. That is boosted enough,
to drive eleven LEDs in series (3.2V x 11 = 35.2V). So a switching
power supply of some sort, converts VBL+ into a 35.2V source. The
LED string runs at 20mA. Probably a 20mA current source, intended to handle
a compliance voltage of 35 to 37 volts (as listed on page 12).

3.3V ---> Run LVDS interface
6-20V ---> Powers LED power supply ---> 35.2V, PWM modulated at LED
string

Another page is hinting, the LEDs are arranged in four channels.
Implying a total of 44 LEDs. 35.2V * 0.02mA = 0.7W or about 50 lumens
(estimated) per chain. Roughly the equivalent of a 20W lightbulb, in
terms of total light output from 44 LEDS.

The PWM control signal on the cable, is a 5V logic level. It is
intended to operate between 200Hz and 1000Hz (above flicker perception
range). The control range is listed as 10% to 100%, meaning PWM doesn't
go to zero on its own. There is also an Enable signal.

The pinout is on page 14.

PWM control is on pin 35.
Enable control is on pin 36.

To light the panel, Pin 36 must have a voltage
above 2.0V on it. A logic low (<0.5V), turns off the
backlight completely.

With Pin 36 logic high, the PWM Pin 35 control takes over.
The PWM must also be logic high. And the percentage
of the time the 200Hz signal is high, determines the
intensity of the LEDs. For example, if it did this, the
backlight would run at about 70% or so. As the signal
is high, 70% of the time.

2.0V +----+ +----+ +----+ ~200Hz

| | | | |
<0.5 -+ +-+ +-+

Page 20 of the data sheet, covers sequencing. You're supposed
to apply panel power (3.3V) before LED power (6-20V). And
the pin 36 Enable is used to gate the PWM for some reason.
They mumble something about latchup (panel stops working),
if the sequence is not obeyed. From one perspective, there's
no reason for the LED supply, to have anything to do with
the LVDS end. It implies that perhaps, the same boosted ~35V
internal supply, might also be used to run the LCD panel
horizontal and vertical driver chips.

In any case, you have a delightfully contradictory document
to work with. (I.e. Page 25 warns of "fluorescent lamp", when
the stupid panel is LED based. Hahaha. Copy-paste-twits)
Yes, there is a slight shock hazard, as the LED chain runs
at 35V, so don't run your bathwater, and reach out and touch it
Who knows, the actual LCD panel driver pins, may have more
voltage than that, but they're not required to tell you
about those. As they're not an "interface" issue. Purely
an internal design issue.

You can see in the Ebay photo, there are places to probe with
your multimeter, if you're bored.

Have fun,
Paul

Thanks Paul,

This is very helpful. I appreciate your suggestions and time.

 

[t]

Could be a problem in switching to/from laptop/dual/external monitor
modes. The laptop has its own monitor mode, obviously. Another is to
show the display on both the laptop monitor and the external monitor
(which shares the same resolution and probably means lower on the
external monitor). Another might be to only show the display on the
external monitor (since it probably has higher resolution). Hitting
the Fn and the monitor key rotates between the monitor modes. Make
sure during testing of the laptop monitor that the laptop is
configured to only use its own monitor.

Have YOU seen the symptom? Or has just the user told you about them?
If you haven't seen them and the user only told you about them then
maybe the user is accidentally pressing the wrong keys and has been
toggling the display mode.

I have not seen the issue. I returned the notebook to the user and have
not heard back so guess the monitor is fine for now.

Thanks for your suggestions and time.