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X301, no backlight after cleaning up

X200, X201, X220 (including equivalent tablet models) and X300, X301 series specific matters only.
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SasQ
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X301, no backlight after cleaning up

#1 Post by SasQ » Sat Aug 04, 2018 12:42 pm

Recently I was trying to clean my ThinkPad X301 due to overheating problems.
I took it apart according to the instructions in the Hardware Maintenance Manual, cleaned up the fan, replaced the thermal paste to a new one, which required me to detach the LCD screen in order to get to the motherboard and the cooling system (unless I'm missing something and there is a way to do that without detaching the screen? :q ), and assembled it back. But after powering it up, the screen is dark :| When I look at a right angle, I can see some characters displaying on it (some BIOS messages), so I guess the motherboard is working fine. The fan is spinning, there's no overheating (at least for now), but the backlight of the screen is off, and I don't know why, and how to fix it :(

The cables are connected the same way as they were before I detached them: there's one on the left (but it doesn't seem to be related to the display, because when I detached it, the characters were still displaying, so my guess is that it's for the camera on the lid), and one on the right, wrapped in some tin foil. Both attached as before.

There is a third one, a single wire, with a metal loop at the end, that was originally conneced to the motherboard with a screw. At first I forgot to attach it, but it is attached now and screwed. Could it be that I forgot to attach it at first that might have messed up my display? :?

But most importantly: any ideas what might be broken and why, and how can I fix it? The display was working just fine before, and the only thing I did to it was that I detached it, cleaned it up with a soft napkin with a bit of rubbing alcohol, and attached back. Nothing hardcore there.

I found in another topic that someone else had similar symptoms and the cause was that a fuse on the motherboard was broken and needed to be replaced. How can I find out if this is the case in my situation too, and where is that fuse located exactly? Can I safely try shorting it to see if the backlight will reappear? (before I properly replace it, of course, in case it will turn out it's broken indeed).

Edit:
As an additional info which I think might be relevant:
From some time ago, I was hearing some weird noises coming out from inside of the laptop, like a high-pitched hiss, somewhat similar to the sound of a connecting modem. At first it was rather quiet, but later it become much more noisy, especially when I turned the laptop off while having the charger still connected. I see some correlation with what appears on the screen and the volume of the noises. When the screen is off, the noise is loud, but the more is going on on the screen, the noise becomes more silent. And it hisses only when the charger is plugged. When I unplug the charger and power it from the battery only, there's no hissing.
So my thoughts wander around a broken inverter, because as far as I know, it raises the voltate, so there is a voltage converter in there, and they have a tendency to hiss when you ignored them for too long :q Could it be a broken inverter then? (But it would be somewhat weird: why did it break only now, after unplugging the screen and plugging it back? :q )

Another think that comes to my mind, is that the laptop may think that the lid is closed, so it turns off the backlight (shouldn't it also turn off the display too, though?), if the sensor that recognizes that the lid is closed is broken from some reason. In that case: where can I find that sensor and check if it's broken or not? It might be broken if it is located somewhere in the palm rest, because I was cleaning it quite intensively today, with water, so maybe something hasn't dry out properly?.. Hmm...

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Re: X301, no backlight after cleaning up

#2 Post by shawross » Sat Aug 04, 2018 5:52 pm

An X301 overheating is something I have never seen.

Did you remove the battery before you started cleaning or opening the chassis?
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Re: X301, no backlight after cleaning up

#3 Post by SasQ » Sat Aug 04, 2018 6:21 pm

shawross wrote:An X301 overheating is something I have never seen.
It wasn't turning off, just heating a lot whenever I tried to do something more CPU-consuming.
Probably because a lot of dust trapped inside the fan (I could smell it frying inside when it was running).
That's why I decided to clean it.
shawross wrote:Did you remove the battery before you started cleaning or opening the chassis?
Yes. As the Maintenance Manual recommended. Same with the charger. I tend to avoid plugging stuff to/from the motherboard while it's powered on, that wouldn't be the smartest thing to do, would it? :q Unless I did it by mistake/overlooking, but it's quite unlikely.

After I cleaned the fan and changed the cooling paste, I plugged the charger to the motherboard to test if it's still working fine (I saw most of the repair dudes do that when they do board-level repairs, so I guess it's OK?), with just the keyboard plugged in (since it has the power-up button), but from some reason it seemed dead at that time, so I unplugged the charger and hooked up the display and the palm rest, then plugged the charger again, and this time it flashed the LEDs for a moment, turned the fan, and turned off immediately. I repeated this a couple of times, with the same result, so I concluded that it might have require the battery to be attached too, so I attached it (the LCD screen was already reattached at that time), and this time it seemed to boot up, but the backlight didn't work.

(Side question: is it supposed to work this way with ThinkPads? Cannot they be run without the battery plugged in? Or is it something wrong with mine?)

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Re: X301, no backlight after cleaning up

#4 Post by shawross » Sat Aug 04, 2018 6:47 pm

The battery is in the front and can be almost unobtrusive so you can almost forget it's there on the X301.

You sound like you have a power circuit issue but you might have another issue caused by your cleaning.

I wonder if you have water in the keyboard. Maybe try to dry it out more to see if that helps.
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Re: X301, no backlight after cleaning up

#5 Post by SasQ » Sat Aug 04, 2018 7:26 pm

Although it is highly unlikely that I forgot to take the battery out (it's also quite heavy, so I would notice), what consequences could that cause if I did?

As for the water: actually the keyboard is the only part that I didn't clean yet, because I spared it for the end.
And the only thing that I cleaned with water, was the palm rest. But I left it to dry on the sun and fresh air for quite a while.

However, let's focus on diagnosing the problem, shall we?

I have a multimeter, so I could check the voltages on the motherboard (at least the places not covered with that black bodybag foil :P ) if you tell me where should I look and what voltages should I expect there.

I found some schematic of the motherboard too. Although it seems to have a couple of pages missing/blank (unless it's on purpose?), and some wacky Chinese letters watermarked on every page, it's still a schematic.

And I already found the BACKLIGHT_ON line on page 29: it's pin 27 of the J5 connector which is detoted as IPEX 20323-040E-11. But they don't tell what voltage should be there. There's also PANEL_BK_T_CTRL (pin 26 of the same, BRIGHT_PWM). They come from pages 9 and 72. There's also a fuse on pin 20 (VCC3B, which I suppose is supplying power to the display?). The LID_SWITCH signal seems to be coming in from the other connector, J705 (20323-030E-11), from pin 5.

But they don't show any voltage values, nor where to find those elements (i.e. the fuses) on the board (except the connectors, which were quite easy to find, since they're big).

Now, can I safely plug in the charger to the motherboard with everything (including the display) disconnected in order to measure the voltages on these pins? If not, how else can I measure these voltages to see i they're there? (And what values should they have? :q )

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Re: X301, no backlight after cleaning up

#6 Post by axur-delmeria » Sun Aug 05, 2018 3:22 am

SasQ wrote:
Sat Aug 04, 2018 7:26 pm
Although it is highly unlikely that I forgot to take the battery out (it's also quite heavy, so I would notice), what consequences could that cause if I did?
IIRC you can blow the backlight fuse if you plug in the LCD connector while either the battery or charger is connected.
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Re: X301, no backlight after cleaning up

#7 Post by SasQ » Sun Aug 05, 2018 6:25 am

Which fuse is this and where I can find it on the motherboard?
I'm looking at the motherboard around the right-hand LCD connector and the charger connector (J24).
I see a couple of tiny elements, some of them might be fuses:
F7 (a really tiny one, if this is the one): 2.7Mohms ... broken?
Unless it's the cap (C724, 10nF/25V), and the fuse is the big one next to it, with "000" inscribed on it, then: 0 ohms;
F3 (next to the Q22 and the VGA port connector): 0 ohms;
One unmarked on the PCB, with "F" inscribed on it (bottom-left from Q5): 0 ohms;
On the bottom side of the PCB:
F2 (on the left of C676 and above U30): 0 ohms;
F1 (surrounded by some three-legged transistors, and U38 on the right): 0 ohms.
So I guess the fuses are OK?

Now I would like to check the voltages on the connectors. How should I do that?
Can I just plug the charger (and possibly battery) with just the keyboard attached?
(Unless there's some other way to power it up without using the power-up button on the keyboard? E.g. shorting some pins or test fields?)

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Re: X301, no backlight after cleaning up

#8 Post by RealBlackStuff » Sun Aug 05, 2018 7:34 am

Check that F7, most likely it has the letter P on it, which means 3Amp
They are size 0603, very fast acting, such as Littelfuse 434 Series.
They are 32V, the 3Amp would be P/N 434003
Probably replaced now by newer fuse 0467003.NR
That would be your backlight fuse.
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Re: X301, no backlight after cleaning up

#9 Post by SasQ » Sun Aug 05, 2018 6:49 pm

Thanks for your post, it was very informative :thumbs-UP: However it doesn't quite match what I see on the motherboard :??:

OK I mapped that part of the circuit using multimeter in diode mode to figure out which is which and compare to the schematics.
Here's the result:

Image

And the schematic for comparison:

Image

On closer look, the part denoted on the silkscreen as F7 turned out to be a capacitor (C724, 10nF/25V), which explains the huge resistance. The actual F7 fuse turns out to be that big element with "000" printed on it. And it has 0 ohms indeed, so it doesn't seem to be broken. And indeed it comes into the three pins of the display port connected together (31, 32, 33 = VBL20, or "Voltage for the BackLight, 20 volts", I presume?), next to another connected triplet of grounds (28, 29, 30), exactly as on the schematic I use.

There's another fuse that is not denoted on the silkscreen: the one on the left, with "F" printed on it. It connects the VCC3B line to the display port's pin 20 (also connected to pin 36, which is V_EDID), so it is the R9054 or FUSE_0603, 434500 on the schematic, and this fuse is also 0 ohms.

Just next to it on the right is another fuse, with "101" printed on it that connects the VCC5M line to pin 25 (VCC_LED) of the display port, and it has a resistance of 100 ohms, exactly as on the schematic. This is the R9043 or R_0805 on the schematic.

Another one is on the right of the MOSFET (Q22), with a little "o" or zero printed on it. It connects to the VCC3M line and converts it to VCC3P that goes into pins 38 and 39 of the display port (VDD). The MOSFET is being opened by the signal VCC3P_DRV that goes to its pin 4. This is the F3 fuse on the schematics (R_0603).

All of the fuses mentioned seem to be OK, they all have small resistance (usually 0..1 ohms, except that "101" which has 100 ohms).

So I guess the next step is to actually measure the voltages on those pins of the display port - in particular, pin 27 = BACKLIGHT_ON, pin 26 = PANEL_BK_T_CTRL (brightness control), and 31,32,33 = VBL20 - to see if they're all present and having correct values. How should I do that? Is it OK to plug the charger and battery to just the bare motherboard + a keyboard required to turn it on? I suppose it has to be turned on and working for these voltages to be present, because the display must be up and running?

In the meantime, I'll try to test the cable while the display is still detached.

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Re: X301, no backlight after cleaning up

#10 Post by SasQ » Tue Aug 07, 2018 6:06 pm

OK I checked the LVDS cable for continuity with my multimeter in diode mode, and it seems to be fine. The pinout on the screen end seems to be a bit different than the pinout on the motherboard end, but I guess it's supposed to be that way, and all the wires responsible for the backlight are OK.

In the meantime, I tried to run the motherboard on the battery only, and it seems to run fine, no weird high-pitched noises, no bootup problems, everything is fine, except the backlight. When I connect the charger, the motherboard starts to make weird high-pitched noises again, and a high-frequency clicking can be heard. So I disconnected the charger, and I noticed that its LED blinks very fast, and when I put my ear close to it, it also makes those high-frequency clicking! :P So I measured the voltage on the charger and... I was stunned: 6..8 V instead of the expected 20V! :eek: I wonder how it is even possible that the laptop worked with this charger for so long. My guess is that it switches the power on and off very quickly, so the laptop is switching between power-saving mode very quickly as well, still charging the battery though, and running from the battery as a kind of a buffer that smooths out the voltage.

So that's why I couldn't run it with just the charger before! :roll: The voltage was too low, so it couldn't run without the battery smoothing it out and raising to the correct value. That's why when I was trying to power it with just the charger, it just blinked the diodes and turned off instantly.

So I swapped the charger for a backup one, and this one seems to work fine, no high-pitched noises etc.

Still no backlight, though :q

So I measured the voltages on the LVDS port. First with just the battery:
VCC3P = 3.4 V
V_EDID = VCC3B = 3.4 V
VCC_LED = 5.2 V (but this one turns out to be just for powering the LED that lights on the keyboard from above, irrelevant to backlight)
VBL20 = 12.1 V <---- This is the power for the backlight, I suppose.
Now after connecting the old charger, this voltage goes up to:
VBL20 = 14.9 .. 15.1 V
which makes sense, since the screen was always dimmer when running from the battery only, and lightened up when I connected the charger.
When I connect the new (backup) charger that works fine, this voltage goes up to the nominal value from the label in the schematic:
VBL20 = 20.0 V
so I guess the voltage for the backlight is fine?

Then there's the BACKLIGHT_ON signal, which is pretty much always 3.4 V when I measure it. Sometimes I noticed it dropping to 0V, but only for a second or two, maybe when the screen was rebooting or I didn't touch it with the probe with enough contact.

So now we're getting somewhere, I guess? 8)
First, the power supply problem and weird high-pitched noises is gone; replacing the old (possibly broken) charger with a backup one solved it.
Second, the fuses seem to be fine, so as the voltages on the LVDS port, and the LVDS cable, right?
(Provided that BACKLIGHT_ON being 3.4 V means that the backlight is supposed to be on.)
So two oprions down, two more to go:

1. The lid closing sensor (turns off the screen when the lid is closed, so it might be turning off the backlight if it doesn't work properly).
2. The inverter inside the lid/screen might be broken, so even if the voltages are OK, it won't turn on the backlight.

How can I check now which option is the actual cause?
E.g. how can I check the inverter? What voltages should be there? (I heard that there are some high voltages there :q )

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