Dead R400?

[harshbarj]

I picked up a "dead" Thinkpad R400 from the thrift store the other day to tinker with and found it was actually perfectly working, minus a busted LCD. I connected it up to an external monitor and plugged in a SSD. Everything worked (note past tense )

I decided to test the LCD port, but did not have the same LCD to test with. I did however have one I tested a T61 with. It was a much higher resolution than it expected so the outer edges were garbled, but otherwise the port worked (You would have had to seen the LCD, someone went medieval on the thing. No other damage was on the laptop, it looks new otherwise). I powered down and connected the old broken lcd back up. That was the last time it fully powered up. After putting it back together I powered it up, the lights flashed then went out. To try to power back up, I had to unplug the laptop and plug it back in. But same thing.

Now clearly the CPU and chipset are partly working because if I remove the ram, I get an error beep that there is a ram problem. I have also gotten a proper replacement LCD, but nothing has changed. LCD, Ram, and PSU are all verified to work with other laptops.

[axur-delmeria]

Playing around with LCDs, especially on Thinkpads, can lead to all sorts of problems unless:

1. You have obtained the datasheets for the LCDs and verified that the pinouts are exactly the same

2. You never forget to remove the main battery and the AC adapter before fiddling with the LCD cable.

Most of the issues are the result of one or more blown fuses on the system board. These fuses are usually located near the LCD connector, but you need the schematics for the R400 to find out their values so you can order replacements.

Try this:
1. Disconnect all power sources (main battery, ultrabay battery, AC adapter)
2. Remove the CMOS/RTC battery
3. Disconnect the LCD cable from the system board.
4. Wait for a few hours to ensure that the CMOS RAM loses its contents, which will force the BIOS to revert to default settings. Alternatively, you can use the "30-second salute" (press and hold the power button for 30 seconds)
5. Connect a monitor via the VGA port.
6. Connect the AC adapter, power up the laptop.

With the CMOS data reset and the LCD cable disconnected, the laptop will use the external monitor as its primary display.

[harshbarj]

This is the first time I have seen a laptop killed just switching LCDs. I have built up dozens of laptops from bits lying around and from visiting the local store ($16 per "dead" laptop, worth it just for parts most times. Many times they just need ram and a hard drive.).

I'll take out the cmos battery tonight and try powering it back up when I get home. Would love to get this working. The 20 min I was running linux mint on it was impressive. Not going to play many 3d games, but would be a great programming laptop. Luckily a new motherboard is just $30.

[axur-delmeria]

Try finding a spare LCD cable too, just in case.

[RealBlackStuff]

Virtually the same schematics as the T400.
Google is your best friend...

[harshbarj]

My best guess now is something is tripping a polyswitch. I know there are at least two of them in the display circuitry,perhaps more, but don't see how they could be killing the power to the whole laptop. Guess the next step is to take the laptop apart and test the power circuitry while powered.

---edit---

After looking the schematic over, and assuming both the t400 and r400 use the same fuses, it can't be the power supply. The t400 uses a fast blow, singe use, fuse (From the part number given). So F2 should be good. Suppose I could desolder them and test them out of circuit just to be safe. Should take just minutes to test them all. But if it's a polyswitch that is being tripped, testing them out of circuit will not help.

I wanted a project, Now I have one . I'm likely one of the few that enjoys board level work.

[harshbarj]

I let it sit for nearly 24 hours, and with the lcd disconnected it boots fine.

If I connect even the bare cable with nothing attached it power cycles. If I boot and try switching to the internal LCD it powers off. I don't see any damage to the cable, but the original lcd screen itself took several heavy blows, so it could be internal damage I can't see. My moving the cable so much to plug in the other lcd may have been too much for it.

I tested the display again on my junk r61, it still works. So off to buy a cable and hope that's the problem. If it still has issues then it must be the LCD circuitry on the main board.

[axur-delmeria]

The symptoms actually sound like a Thinkpad with a blown/damaged LCD fuse.

[harshbarj]

The symptoms actually sound like a Thinkpad with a blown/damaged LCD fuse.

They have tested good.

I have found out it's not the LCD cable either. So I have a new cable coming for no reason. Even with the whole LCD assembly removed when Linux tries to activate the internal LCD the laptop powers off and I have to unplug the power to get it working again.

Going to check the AC adapter just to be safe. As long at it's a small component that has failed I'm good.

[harshbarj]

It was F14. Which is odd because that is a polyswitch for the docking connector.