Motherboard Fault Analysis - Help Wanted!

[lmt41p]

In my few days on this forum I've learned that there is a enormous pool of knowledge and experience about all things Thinkpad related. I'm hoping that some of you will reflect on this motherboard fault analysis problem and pass on your thoughts, which will help me decide what to do with my crippled T41p and two LCD panels.

I think I damaged my motherboard while attempting to replace my LCD panel, whose backlight had failed. The disassembly and reassembly procedures seemed to be error-free. I believe that the replacement LCD panel, an ID Tech P/N 11P8346 version IASX16S, is the IBM version of this panel, although I purchased it not from IBM but from a reputable online vendor. A detailed description of the behavior of the T41p after the replacement is described in this post. The summary of the resulting fault is as follows:

- without an external monitor the system attempts to power up for a few seconds then shuts off, never making it POST screen;
- it can boot with an external monitor;
- it can only operate in VGA 640x480 mode;
- any attempt to change resolution causes TP to immediately shut off, as though a component is shorting

My fault analysis objectives are: 1) try to determine which step in the LCD replacement caused the failure; 2) identify likely failed mobo component(s); 3) determine if the step that precipitated the fault also damaged either the new and/or old LCD panel (which I re-connected during problem determination); and, 4) determine if the failed mobo components can be repaired.

I'm sure everyone claims this, but I don't think I did anything wrong during the dis/re-assembly. I didn't have a grounding strap, but I was cognizant of this and took precautions. The exposed planar was protected from debris. No antenna wires or daughterboard cables were abused. The only doubt I have is if, in my eagerness to test the new panel, I did not plug in the lcd harness cable properly. It felt as though it was seated properly and I replaced the tape that fixes the ribbon connect to the LCD circuit board. While reviewing my steps I wondered if I could have slipped the ribbon cable plug under the lcd connector, causing the pins on plug to short on the metal casing of the connector. I think I would has noticed such a mistake when I disassembled the screen after the failure, but I was upset and cannot recall. I don't have any other theory about what I might have done.

So now I have my old LCD and a brand new one, neither of which will work with the T41p. Both might be functioning, albeit the old one needs a new CCFL. I might only have blown the T14p planar fuses, but I'm having a hard time imagining how that would cause the system to shut down when the graphics resolution is changed. I mean, as soon as any graphics related function is attempted the system dies. This seems to point to the GPU. But if the GPU is fried, how can the system boot in VGA mode?

I have borrowed a T40p SXGA+ in perfect working condition for disaster recovery. I am extremely nervous about trying to test the new LCD panel with this T40p (to see if works) because I don't want to fry it as well. But maybe it can serve as a reference for testing components on the T41p planar. I may have access to an oscilloscope which I could use to map the signals on a few key components. I suspect I'd need a logic analyzer to do any meaningful component-level detective work. I found a procedure in a forum post for testing mobo fuses with a multimeter and I will perform it shortly.

Several threads on the forum reference reflow soldering of the BGA as a solution to many GPU and boot problems. I'm assuming that these are problems whose causes are mechanical in nature - planar stresses or manufacturing defects - rather than problems resulting from an electrical mishap. I'd happily pay for a reflow if it solved my problem; I'm not convinced yet that it will.

My apologies for such a long, drawn out explanation, but this is my predicament. I really like my T41p and I would like to restore it to full function if possible.

Thank you in advance for your consideration.

[jamerslong]

I agree with you, a reflow would be futile as this is an electrical failure.

could you look over the HMM for possible fuses?

[lmt41p]

The HMM that I have doesn't have show any fuse locations; I guess they aren't considered field replaceable. I suspect planar schematics or circuit board templates are hard to come.

[jamerslong]

I havent heard of such schematics existing, it would be worth a shot to open her up and take a multimeter to allt he fuses. I would assume there would be fuses for these things since it's obvious this things can happen.

the only other thing i can thikn is a shorted out Controller chip that would need replacing.

[Harryc]

The part you've listed is a valid replacement LCD for a 14" SXGA+ T41P. If it were my machine, I'd disconnect the internal LCD at the systemboard and then see if the symptoms change on the external monitor. If the symptoms do not change, then it is a systemboard issue. You could also apply pressure to the GPU itself on power up to see if the symptoms change. I've never heard of a fuse just for the external LCD, but I suppose it's possible.

[SMA]

Try to take a look at this
http://forum.thinkpads.com/viewtopic.php?f=2&t=70637

[lmt41p]

The fuses mentioned in the topic are encouraging - thanks. I'll test them today. Anyone know of a source for these fuses, other than another T4x motherboard?

[sktn77a]

Could it be bad video memory? With the internal LCD the system might be trying do something different from when attached to the external monitor and just failing at the video check phase. Changing resolution on the external monitor probably uses additional video memory which could cause the system to crash if this memory is bad (?). This possible explanation, of course would not be good

[lmt41p]

I neglected to mention in this thread that my motherboard passed PC Doctor tests for everything, including the graphics subsystem. However, I could not see the graphics tests as they executed, which I normally can on the LCD. The computer did not shut down as it executed these tests, like is does when attempting to change graphics characteristics under WinXP.

This would suggest that the GPU is OK insofar as the CPU is concerned, and that the PC Doctor tests don't drive the same mobo components as WinXP.

Browsing around I've become more informed about the Mobility Radeon GPU. It supports independent analog and digital outputs; this is why the T41p can operate with the LCD removed, in external VGA 640x480 mode. Given that the analog output is working I'm guessing that something on the digital video output paths of the mobo was damaged - except that the system shuts down even on the analog output when I try to increase display resolution.

Does anyone know if the Radeon GPU has internal video memory separate from the BGA video memory? Maybe 640x480 mode uses this internal memory, or even mobo RAM, but higher resolutions require the BGA memory and as soon as it is accessed something shorts and the TP shuts down.

[RealBlackStuff]

Maybe the LCD cable got damaged during the swap.

Assuming you followed Harryc's advice about disconnecting the LCD cable and external testing, and things went OK so far,
exchange the whole lid with that spare one from the T40p and see how that goes.

[lmt41p]

I have tried harryc's suggestion and the TP ran on the external drive just fine. I also discovered that 640x480 is only the max resolution under WinXP using the specific ATI drivers.

In Safe Mode I could run video up to 1280x1024 with generic drivers (the 1400x1050 mode was not available under the drivers loaded in Safe Mode). This intrigued me and I theorized that the GPU and BGA RAM were just fine, only the digital video outputs were toast. To test this I did something that in retrospect was kind of dumb. I pressed Fn+F7 while in 1280x1024 mode to switch on the digital video output. The TP promptly died and now it won't even boot with an external monitor. It powers up for a few seconds then dies, like it did when it was trying to power up without an external monitor.

I'm guessing that whatever was partially fried before is totally fried now. I will pull the motherboard and test the fuses. There is no point in swapping the T40p lid to the T41p if it won't even boot to an external monitor.

And still, I have no clue as to what caused the initial failure. Maybe the lcd harnass developed a short when I separated it from the old panel, even though I was very careful. I can't imagine a static discharge wreaking such extreme damage.

Does anyone actually repair motherboards, other than reflowing or reballing them, even IBM/Lenovo themselves? Are they essentially a throwaway once they develop a fault? Except for the members on this forum who replace fuses and such, is there a viable business fixing fried mobos? Inquiring minds would like to know

I appreciate everyone's comments and suggestions. I'll continue to post updates. Please keep the ideas coming.