HDX inverter/backlight failure

[HaggisCat]

Yes it can be a little nerve wracking at first after a repair, but this will go away.

 When you have a chance, hit one of the kudos buttons, thanks. 

[guilliamo]

Have an APPARENTLY similar problem with my HDX18t-1000: (Using Pelikanol's info layout)

Some of the symptoms:

• The image is displayed on an external monitor.
• I can see the image on the laptop LCD, but it is very dim. It does adjust & at full brightness is ALMOST usable in a completely dark room.
• There were signs of a display failure prior to it going so dim. Display would sometimes come back to life if computer was restarted.

What I have tried already:

Replaced inverter with a USED unit from eBay with NO change in symptoms.

Replaced inverter with a NEW unit from eBay with NO change in symptoms.

Tried a test LCD lamp on one connector at a time and test lamp is also dim.

I followed the manual instructions EXCEPT that I did not remove the screen first. IT appears to me that the HP instructions are based on treating the screen assembly as a repairable unit and there is no upside to completely disconnecting the screen if you are just replacing the inverter.

While it is possible that I've got THREE bad inverters, that seems unlikely. Sooo I think that some input to the inverter is incorrect, either a cable problem or something on the motherboard.

Does anyone have a pinout of the inverter input ? Other ideas ?

Thanks !

G

[guilliamo]

No progress so far, but think I've figured out the inputs:

Pin 1 = V+ 

Pin 2 = V+

Pin 3 = Control (On-Off)

Pin 4 = Brightness (Analog)

Pin 5 = GND

Pin 6 = GND

The TDK inverter circuit board has convenient small copper pads to which I soldered wires to I could test the voltages present safely.

I get:

V+ = 19.2V

Control = 3.1V with lid open & .34V with lid closed (would appear to indicate that lid switch is not a part of the problem)

Brightness = 1.05V (min brightness) & 3.1V (max brightness)

Of course, max brightness is still VERY dim.

Don't see any evidence here of a cable problem & the INPUT voltages are what I would EXPECT to be normal.

Will build a test rig to see if increasing the brightness beyond 3.1V to 5V or so adds any brightness.

Am now suspicious that BOTH replacement inverters are defective (as is original stock inverter) unless the Brightness voltage is too low.

G

[HaggisCat]

I followed the manual instructions EXCEPT that I did not remove the screen first. IT appears to me that the HP instructions are based on treating the screen assembly as a repairable unit and there is no upside to completely disconnecting the screen if you are just replacing the inverter.

 ________________________________________________________________________________________________

 Remove the cable from the back of the screen and try your inverter(s) (any one of them) with your test lamp. The cable should only be plugged into the mother board and your inverter The "HP" LED logo light on the back cover has to be disconnected too. I am also going to assume that you know your test lamp is a good specimen.

 With the cable connected only to the inverter and MoBo, power up the laptop and if there is no full brightness to your lamp, gently move the video cable around where it passes through the hinge area. A cable can look OK from the outside and still have broken wires inside.

[guilliamo]

Haggis-Cat: Thanks for the quick get-back !

I'm out of town for a few days before I can go back to the HDX18t.

Still want to find out what happens with the display when the control voltage is increased from 3.1V to 4V or 5V; will do that on Thursday.

Am operating on several ideas/assumptions which may not all be correct:

1) The HP logo is lit by an LED and is only related to the screen lights by the fact that it gets power from wires in the same cable nest as does the video and inverter cables. It IS normal brightness by the way.

2) The stock screen is dual lamp...two independent lamps at the top and bottom of the screen. Seems unlikely that BOTH lamps would become equally dim at the same time. Other LCD CCFL backlight failures I've seen involve the screen going pink as the lamp fails, but may not always be the case.

3) The voltages at the input of the inverter are are normal/correct, with the possible exception of the brightness control which MAY need to go closer to 5v (than the 3.1V I get) for full brightness.

When I use the test lamp as you suggest (except that I did not disconnect the HP Logo cable), the test lamp is white but dim on either inverter connector. Gently moving the cable made no difference.

Thanks again; Will post results of Thursday's tests.

G

[guilliamo]

Thursday tests:

Wow. Looks like I'm making this too hard.

Using a completly independent power supply to drive the inverter, I get no change in symptoms.

1) Screen is still very dim, but it is dimmest on the left side (facing screen).

2) No increase in brightness if pin 4 is increased above 3.1V

Test lamp is full brightness if connected to either connector as long as the screen ccfl leads are unplugged.

If  I unplug the red/white screen ccfl connector, screen is actually a little brighter, but shuts off in a few seconds. If I unplug the blue/black ccfl connector, no screen lamp.

Soooo, I'm thinking that one of the screen cccfl lamps has failed (the one connected to the red/white connector) and the simplest analysis is correct:

The symptoms indicate either a screen backlight failure OR an inverter failure; replace inverter with no change in symptoms = screen backlight failure.

I suspect that the ccfl arrangment is one on the left and one on the right, and the left side has failed, but is still drawing current.

G

[HaggisCat]

I was wondering what your test results would yield, but when you said "that one used and one new inverter made no difference", then the backlights them selves were suspect.

 You can replace them, but that's akin to working on a watch, or buy a new screen. You can also get an entire screen assembly, new or used.

 http://www.laptopscreen.com/English/currency/USD/laptop-part-number/HP-Compaq/HP%20HDX%20X18/

 They used the matt one. It's a bit of a bear getting the screen out, even after you remove all the screws the screen is still held in their with this industrial 3M two sided tape. If you get a very hot hair drying and hold at the top corner at the front, the adhesive slowly starts to soften so you can gently pry it off. Take you time here. It's best to start at one of the top corners because there is the least amount of adhesive there.

 If you do decide to replace tha lamps e-bay is you best bet, the wires on the new lamps are too thick, so you will have to reuse you old wires. The lamps are both at the bottom incidentally and the screen is probably made by Samsung.

[guilliamo]

HaggisCat: Thanks for the advice & encouragement !

1) I had already ordered a screen form < http://www.laptopscreen.com> when I got your note. (Great minds, etc., etc.)

2) Screen they sent is a Samsung LTN184T03, apparently identical to the original/stock screen.

3) After disconnecting the video cable and the webcam and pulling back the webcam cable, I removed the 8 screws holding the screen & bezel to the hinge brackets. Soooo I had just the screen & screen bezel free of the HDX18. Used a credit card to pry one corner free, and then used a long piece of dental floss to work down one side and then across the screen to free it from the bezel.  Only took a minute or so....just have to work the dental floss around each clip to keep it between the screen and bezel with no interference. Did NOT have to resort to a hair dryer, but had one in standby.

4) Reassembled with new screen and fired it up and all is well ! I think I'd forgotten just how bright a brand new ccfl screen is.

5) As with getting access to the inverter, see no upside to completely removing the screen assembly from the HDX18. My thought is that every screw not removed can't be misplaced or stripped and every cable not disconnected is less likely to be damaged. Having replaced the inverter twice and the screen once, think I could now do an inverter in less that half an hour and a screen in 45 minutes. 

Thanks again !

G

[HaggisCat]

That's excellent, I would have never thought of using a piece of dental floss.  Don't throw your old screen away, the lights are still replaceable, and even in the state that it's in you can still get a few bucks from e-bay.

[gierso]

i have the same problem as pelicaniblahblah im about to embark in fixing my beloved hdx 18 1020us

im just ordering the inverter for now

i hope its enough to fixit and the backlights dont need to be replaced.

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