Thinkpads Forum

Posted: **Fri Dec 30, 2022 3:43 pm**

Hello dear community,

I have broken T400 with switchable GPU (2765-21G). Its display does not show any image, external display works. Recently I noticed different behaviour of the internal display when using integrated or discrete GPU. Since I could not find an explanation for it, I decided to ask people here.

So, here is my test scenario: T400 connected via docking station (VGA port) to external display. I boot it with Linux Mint 19 live USB, setting different options for GPU in BIOS. The results are as follows:
- in BIOS set integrated graphics: when switching between external and internal display, internal becomes litten up (but without any useful information), or remains dark - when external in use. Besides that, Display setting in Mint allow display mirroring
- in BIOS set discrete graphics: internal display remains permanently dark, and there is no option for display mirroring in Mint setting.

Actually, it looks like AT card does not "see" internal display at all, but delivers image on the VGA output - which means, the GPU itself is fine. Can anyone give me an idea on possible reason? Or - if exist - just give a hint to an existing thread here?

Best wishes for the new year and kind regards from Hamburg / Germany.

Andrey

Posted: **Fri Dec 30, 2022 7:17 pm**

It's difficult to say if it's a fuse issue on the system board, or possibly a bad display itself. I'd lean towards a fuse initially, unless you have another similar-era display you could use to hook up to the LVDS cable of the T400 to test. Also try re-seating the LVDS cable, just in case.

If the display lights up then the backlight works, at least. Usually when a display dies on me it's either the backlight goes out (in LED models they start to go out sequentially instead of all at once), or lines start appearing. Do you know if your T400 has an LED or CCFL display? During the T400 production run you can find both.

It's also worth checking to be sure the Hall effect sensor is working. On these if the LCD is closed there is a small magnet that, in proximity to the sensor, tells the system to shut off the internal display.

I couldn't find any fuse maps for the T400, sadly - anything I did find had broken image links. Look for them marked by "Fxx" (e.g. F1, F2, F3 etc.) on the motherboard. They are very small - usually .5mm or so wide and 1-1.5mm long. Use a multimeter or continuity tester across each side to test them.

Replace with a like voltage/current rating. It's not impossible to do free-hand but you need steady hands and a fine tip on your soldering iron!

Posted: **Sat Dec 31, 2022 2:17 am**

hello,

theterminator93 wrote: ↑
Fri Dec 30, 2022 7:17 pm
It's difficult to say if it's a fuse issue on the system board, or possibly a bad display itself. I'd lean towards a fuse initially, unless you have another similar-era display you could use to hook up to the LVDS cable of the T400 to test. Also try re-seating the LVDS cable, just in case.

If the display lights up then the backlight works, at least. Usually when a display dies on me it's either the backlight goes out (in LED models they start to go out sequentially instead of all at once), or lines start appearing. Do you know if your T400 has an LED or CCFL display? During the T400 production run you can find both.

It's also worth checking to be sure the Hall effect sensor is working. On these if the LCD is closed there is a small magnet that, in proximity to the sensor, tells the system to shut off the internal display.

I couldn't find any fuse maps for the T400, sadly - anything I did find had broken image links. Look for them marked by "Fxx" (e.g. F1, F2, F3 etc.) on the motherboard. They are very small - usually .5mm or so wide and 1-1.5mm long. Use a multimeter or continuity tester across each side to test them.

Replace with a like voltage/current rating. It's not impossible to do free-hand but you need steady hands and a fine tip on your soldering iron!

thanks for the hints. I need to find out what "fuse issue on T400" is, but I also suppose, it has something to do with a board, and not display. This different behaviour on different GPUs is wondering me a lot.

I will not re-solder any items on the board, I am really untalented in it. (several attempts in the past have proven it). I will try to re-seat a connector, but then I will sell this device for spare parts.

Kind regards from Hamburg,
Andrey

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T400 with switch.GPU: internal display blank

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