Problems with display in R400: hint from experts is welcome

[BigCatAndy]

Hello dear community,
I have one hardware problem, which I cannot resolve by myself, and I would appreciate any hint from you.

A friend of mine gave me 2 R400: 7443-E1G ("N1") and 7439-WMH ("N2"). Laptop N1 works, but the display remains dark. External display works. Laptop N2 is dead - according to the previous owner, it has water damage and does not show a sign of life. A friend of mine asked, if I could do anything with laptop N1 using spare parts from laptop N2.

I tried to replace the display - no effect. Same situation - display remains dark. But I found out another issue: when I started Linux Mint from a USB stick on laptop N1, I noticed, that there was no Bluetooth module - although I saw one connected to the system (BCM92046 by Broadcom). This brought me to the following idea: can it be that the display cable is somehow damaged so that it does not deliver backight and Bluetooth? A probability that 2 displays are damaged in the same way is rather low, and Bluetooth module should be seen by the system, if cable is healthy.

I would appreciate any hint, it will help me to resolve the problem. Searching for a replacement display or replacement cable are two different things.

Regards,
Andrey

[ajkula66]

Have you swapped just the panels, or the entire LCD assemblies ?

[kfzhu1229]

By black do you mean the display still displays something but the backlight is dark or there is just no picture even forgetting about the backlight?
Also it does not hurt to try the display cable from the dead R400, but from my experience, water damage on these things can easily result in a dead screen cable as it has 12V even when the system is off and those pins can simply burn away if water drips there

[RealBlackStuff]

Check the backlight fuse F3 (3A, 32V, fast) near the LCD-connector on the motherboard.
It's a 0434003 or 0467003.NR in size 0603.
If dead, piggy-back solder a new one on top of it.

[BigCatAndy]

Hello,
1) I swapped only panels;
2) by "dark" I mean that there is no background light. I can see text and thinkpad logo, when I put direct light on the screen.

The fact that Bluetooth is not recognized, is a hint for a broken cable, isn't it?

Regards,
Andrey

[BigCatAndy]

Check the backlight fuse F3 (3A, 32V, fast) near the LCD-connector on the motherboard.
It's a 0434003 or 0467003.NR in size 0603.
If dead, piggy-back solder a new one on top of it.

Hello RealBlackStuff,

it means, I need a measurement device? And what does "piggy-back solder a new one" mean?

Regards,
Andrey

[RealBlackStuff]

To measure a fuse you need a Multimeter (google it).
But since you can see a vague picture on a dark screen, then your backlight fuse was definitely blown.
Solder the new fuse on top of the old one (this is called piggy-back or piggyback style), rather than try and remove/replace the old fuse.

[kfzhu1229]

Also check the LCD connector for any missing/corroded golden pins. I have a water damaged T520 for parts that the LCD connector on the motherboard has all the 12V pins missing, yet the motherboard still displays perfectly fine with another cable.

[BigCatAndy]

To measure a fuse you need a Multimeter (google it).
But since you can see a vague picture on a dark screen, then your backlight fuse was definitely blown.
Solder the new fuse on top of the old one (this is called piggy-back or piggyback style), rather than try and remove/replace the old fuse.

Hello,

this is a worst-case scenario for me. I'm not really experienced in soldering anything . Actually, I have to check the cable for the damaged pins first. If all pins are in order, I need to measure the fuse and replace it, if needed. Correct?

And what about Bluetooth module? What can be a reason for a module to be invisible in the Linux?

Regards,
A.

[BigCatAndy]

Actually, possible reasons are:
- broken LCD panel
- broken/damaged cable
- damaged fuse - it means, main board.

Correct?

[BigCatAndy]

To measure a fuse you need a Multimeter (google it).
But since you can see a vague picture on a dark screen, then your backlight fuse was definitely blown.
Solder the new fuse on top of the old one (this is called piggy-back or piggyback style), rather than try and remove/replace the old fuse.

Hello RealBlackStuff,
where can I find a new fuse?

Thanks,
Andrey

[RealBlackStuff]

Take the finger out and DuckDuckGo what I told you in my first post in this thread.

[kfzhu1229]

Though I suppose do keep in mind though that there is a chance that the fuse might not be the only thing that is blown.
I remember shorting out the backlight on my ThinkPad T43p motherboard from dropping the inverter into the motherboard when testing. And what ended up happening was not only was the fuse blown, the MOSFETs controlling it behind the fuse also got blown and no longer connect the circuitry to get the voltage delivered when the screen turns on. I have to jump over that MOSFET to get the screen working.

[BigCatAndy]

Though I suppose do keep in mind though that there is a chance that the fuse might not be the only thing that is blown.
I remember shorting out the backlight on my ThinkPad T43p motherboard from dropping the inverter into the motherboard when testing. And what ended up happening was not only was the fuse blown, the MOSFETs controlling it behind the fuse also got blown and no longer connect the circuitry to get the voltage delivered when the screen turns on. I have to jump over that MOSFET to get the screen working.

Hello,
the story became more complicated that I thought... I need to decide for myself, if I continue it, or not... I'm not very experienced with hardware tasks.. Soldering and so...

Anyway, thanks a lot for your hints. I learned really a lot.
Regards,
Andrey