HP M6 Blown transistor on LVDS circiut

[Mad_Professor]

I got a HP Envy M6 in for repair two weeks ago, customer supplied parts, but from what he told me it took a nasty fall and broke apart, screen damaged, lvds cable damaged and shorted (burn marks).

The laptop turns on and boots fine into windows on external display but once I got everything back together and put the new screen in, turn on system, no backlight, system still boots fine, just not displaying anything on the lcd screen with flashlight. So I plug in the old screen the backlight comes on but just displays white, few caps fell off it's controller so yeah no image. I chalked this one up to incompatible or defective screen because it was not the same part number, new screen came with DCR, old one didn't have it.

I ordered a new screen matching part numbers and got it today, this one didn't work either. I took apart the laptop again and pulled the mainboard out examine topside first, nothing of interest, flipped it over and found Q29 has a bubble, got a magnifying glass and took a closer look, looks like heat damage and has small a fracture in it.

Now the number part number on it (underscore is illegible digit) is 01A_
Can't find any others on the board that look like it, seems to be unique to the LVDS.


Now if you reference the photo, top pin to the bottom left pin is shorted both ways, but top to right shows 1.7ohms but right to top shows no continuity.
Left to right shows 1.7 ohms but right to left shows no continuity.

Any help appreciate.

EDIT: FOUND ANOTHER ONE, it's 01A Then letters IL running vertical next to it

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Here's the good one I found, I also found another over near the realtek audio chip, it pcb mark is OL1 or QL1.


Sadly I haven't been able to find a datasheet or who makes this chip.

Need identification and suitable replacement.

[budm]

Re: HP M6 Blown transistor on LVDS circiut

It may be MOSFET or Transistor, the left pin is Base (Gate), Middle pin is Collector (Drain), the right pin is Emitter (Source). So take the resistance reading between the right pin and the ground plane or chassis ground, if it shows < 1 Ohm, then it is more likely to be NPN (or N channel MOSFET).
You can also use Diode mode to test the good one to see how it shows on the reading between Base and Emitter, Base and Collector.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

It may be MOSFET or Transistor, the left pin is Base (Gate), Middle pin is Collector (Drain), the right pin is Emitter (Source). So take the resistance reading between the right pin and the ground plane or chassis ground, if it shows < 1 Ohm, then it is more likely to be NPN (or N channel MOSFET).
You can also use Diode mode to test the good one to see how it shows on the reading between Base and Emitter, Base and Collector.

I did ground to emitter pin, the bad one read 6.5k ohms, the realtek one read 6.5k and other one for the KB backlight read 48k ohms.

Then I switch to diode setting, and measure between gate to emitter.
Realtek: starts at 1.7 Ohms climbs to 1.9 before going open.
KB light: brief reading of 1.9 before going open.
Bad one: 1.7ohms

Then I switched to collector
Realtek: starts at 1.65 climbs to 1.9 before going open
KB Light: Unknown Interference
Bad One: Shorted 0.0 Ohms

[khaahk]

Re: HP M6 Blown transistor on LVDS circiut

may be it?

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

Probably it is an 2301a mosfet (sot-23). Just check gate and source voltage to determine if NPN or PNP

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Probably it is an 2301a mosfet (sot-23). Just check gate and source voltage to determine if NPN or PNP

Tested for voltage, all three have voltage at the emitter, none at the base, did not test collector, will test if asked.

Bad one: 3.3v
Realtek: 3.3v
KB Light: 5v

Also if it helps this is the panel

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

I'm not experience enough in picking transistors.

My guess I need a PNP that can handle 3.3v and is a BJT?

I don't know the specs, what do I need? Are there any I can savage from junk boards? I got several HP and Toshiba that are 100% dead older models with CCFL.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

bump

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

The problem is that you do not have any voltage in the "gate" pin. Post a high resolution picture of the board as well as the exact model of the HP laptop.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Well I know that! It's kind of obvious hence the thing not working, and that transistor being shorted. What I want to know is what a suitable replacement is.

I got voltage at the emitter of all 3, volts posted above.
Only the bad one is not passing voltage to the base/gate whatever you call it.

The model is HP Envy m6-1105dx.

I have bunch of junk hp dv6000, two Toshiba a205, a crap brand everex laptop, a couple of dead dells.

Photos coming....

EDIT: Photos.

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

Check for continuity of the drain pin of Q29 with any of the pins of the lvds connector.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Check for continuity of the drain pin of Q29 with any of the pins of the lvds connector.

Yes, two pins on the left side of the LVDS cable, going left to right, pin 2 and 3 have continuity, nothing else on the cable has anything.

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

Are there any markings on Q28? Check all pins of Q28 for voltages with power(two readings, one with just power supply connected, the second after power button pressed) and resistance to ground without power. Check also which pin of Q28 have continutity with either pin 2 or 3 of the LVDS connector on the board.
What are the markings on the ENE KBC IC?
Can you post the higest resolution you have of the pictures you took of the board on a file share site like "4shared.com"

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Are there any markings on Q28? Check all pins of Q28 for voltages with power(two readings, one with just power supply connected, the second after power button pressed) and resistance to ground without power. Check also which pin of Q28 have continutity with either pin 2 or 3 of the LVDS connector on the board.
What are the markings on the ENE KBC IC?
Can you post the higest resolution you have of the pictures you took of the board on a file share site like "4shared.com"

Q28 markings are MN127 or MN1Z7. The fourth digit is not define well enough.

Next item...

I'm guessing you're talking about the one near KB Backlight and battery terminal.
ENE KBC IC markings are

KB932QF AO
HH-N70G2
AC-121531

I can post bigger ones but it won't be better than what you're seeing.
Actually it'a more like my camera sucks. I can post closes ups if needed. I have no problem doing that.

TESTING Q28 in progress, results next post.
Also if you don't hear anything from me in the next hour or so, I most likely have lost power due to a nasty thunderstorm in progress.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

Q28 RESULTS!

look at with pins on left and right with Q28 Label at the bottom.

UNPLUGGED
LEFT
PIN 1 = GROUND 0.06 Ohms
PIN 2 = NONE DETECTED
PIN 3 = NONE DETECTED
RIGHT
PIN 4 = NONE DETECTED
PIN 5 = NONE DETECTED
PIN 6 = GROUND

PLUGGED IN.
LEFT
PIN 1 = GROUND
PIN 2 = NONE DETECTED
PIN 3 = NONE DETECTED
RIGHT
PIN 4 = NONE DETECTED
PIN 5 = NONE DETECTED
PIN 6 = GROUND

With power
LEFT
PIN 1 = GROUND
PIN 2 = 3.3V
PIN 3 = 3.3V
RIGHT
PIN 4 = NONE DETECTED
PIN 5 = NONE DETECTED
PIN 6 = GROUND

Q28 TO LVDS
LEFT
PIN 1 = GROUND
PIN 2 = NONE DETECTED
PIN 3 = NONE DETECTED
RIGHT
PIN 4 = 100 Ohms to same pin 2 and 3 on lvds cable
PIN 5 = NONE DETECTED
PIN 6 = GROUND


Had to make some correction my memory is shot.

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

You got a problem on your PCH. Q29 is an pnp fet supplying 3.3v power to LVDS. In order for the gate to close you need an enable signal from PCH.
Q28 is a sot 363 NPN (dual fets). One fet closes the 3.3v supply to LVDS (short to ground) and the other accepts to its gate the enable signal from PCH to supply voltage to the gate of Q29 through a voltage divider.
Have a look at a typical COMPAL (your board manufacturer) lcd power circuit



Usually the dual fet pins are: (Q28 in your case) first fet, are pins 1 (ground), 2 (gate 3.3v always), 3 lvds 3.3v power, to close the power to LVDS and second are pins 3 (3v alw voltage divider to supply voltage to close gate of Q29), 4 (connect to ground to enable the voltage divider) and 5 gate (enable signal from PCH).

Your readings do not match the pins usually used, so you have to find which pins compose the two fets. The other thing is that in your case, it probably uses 3.3v suspended voltage instead of always voltage ( you've measured 3.3v after pressing power button).
So, assuming that is the only damage to PCH, you can find a coil with suitable voltage (to substitute the enable signal from PCH) and solder a wire from the coil to the gate of the second fet's gate, to enable power voltage to LVDS.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

So what you're saying is, it's another component that's gone bad (pch) and Q28 and Q29 are ok, they're just not enabling the power supply to the screen board due to the pch being dead or broken. Is my comprehension of that correct, or did I fail professor?

So what will I need to do to find the second fet's gate?

Also you said "solder a wire from a coil" I'm guessing a PI or inductor?
Never done bypass mod before. Closest coil would be PL702 left of Q29/Q28 by an inch.

Gonna need a very tiny wire.
(Gonna need a bigger boat.)

[atsio]

Re: HP M6 Blown transistor on LVDS circiut

I am not saying that Q29 is allright (you need to change it), I am just pointing that by changing it you will not solve your problem.
There is an easiest way. Remove Q28 and Q29 and solder source and gate pins of Q29 together. This way you will always supply 3.3v voltage to LVDS.

[Mad_Professor]

Re: HP M6 Blown transistor on LVDS circiut

I am not saying that Q29 is allright (you need to change it), I am just pointing that by changing it you will not solve your problem.
There is an easiest way. Remove Q28 and Q29 and solder source and gate pins of Q29 together. This way you will always supply 3.3v voltage to LVDS.

What are consequences of doing that?
screen stays on?
back-light doesn't shut off when lid closes?