Thinkpads Forum

Okay, I got my unwell 600X back in order, based on feedback here. Thanks, everyone!

There is one last issue to troubleshoot. This machine, since I bought it secondhand, has had a screen which is slow to fire up the backlight on boot. I can see the ThinkPad splash screen logo dimly visible, but the backlight does not come on until well into the OS boot process.

After that it is usually stable for the rest of the session.

A similar thing manifests itself on wake-from-sleep. I can see, dimly, that the screen is displaying what it should, but the backlight lags behind in activation, often by as much as a minute's time.

I have tried Fn-F7 in both cases, boot and wake, and it does go to the external monitor and back, but without affecting the symptomatic behavior.

I said, "Subcard?" and put in a spare. Same thing. Put in another spare. Same thing.

"OK, inverter then." I swapped to an entirely new screen which had previously worked well. No go. I changed the inverter in that screen. No.

Could both screens have dying CCFLs? They are both at the stage of life where they're a bit yellowed.

Or is there some other device on a 600X which might induce a backlight delay or instability?

It sounds like the subcard might not be getting enough power.

There are a few threads that discuss the proper output of the subcard. You might want to search through the forum for it. I think it is also in the HMM.

One other thing, what are the Voltage and Amperage specs of your power supply? It should be a 56W PSU. (16v x 3.5A)

I have a 600E which exhibits the identical problem, albeit it takes anywhere from 5 to 7 minutes until the backlight finally decides to fire up. Like you, I have changed the Sub Card, the inverter and the LCD panel (which I'm sure had a good lamp but it's been a long time since I've worked on the system). I have decided that something on the motherboard is preventing the lamp from getting the voltage it needs to light. As I only have the one "E" machine, I haven't spent much time trying to get to the root of the problem. I'd be happy to hear from you on what else you have tried to fix the system and/or how you solved the problem.

Chris Thorne wrote:I have tried Fn-F7 in both cases, boot and wake, and it does go to the external monitor and back, but without affecting the symptomatic behavior.

When the backlight finally does turn on does switching the display to the external video port and back to the LCD panel (i.e. Fn-F7) also cause the backlight to go out for a while?

rkawakami wrote:When the backlight finally does turn on does switching the display to the external video port and back to the LCD panel (i.e. Fn-F7) also cause the backlight to go out for a while?

An excellent question!

I had not tried that recently, so I did the experiment just now.

The backlight does indeed stay off for 30sec or so after the display has been switched to external and then back to internal.

As for the voltage question, I will pull up a copy of the HMM and some needle probes for the voltmeter, and see what I can find out.

The power supply in use here is a 16V, 3.36A, p/n 02K6543. I assume that it is nominal. But I can and will test with a second supply just in case, to eliminate the possibility.

Aha! Here is a new datum.

I have a spare display, and spare inverter, and two spare subcards. I played around with various combinations but still got the lagging backlight, or no backlighting at all.

Then I remembered that I had... a spare CCFL! I got that and plugged it in to the inverter in the screen which I had opened. Booted the machine. Hey presto! The CCFL lit right up and stayed lit.

I think that what I had here was a situation where both LCD units had a similarly failing CCFL tube. Not in the way that I recognize. Every time in the past I have seen a dying CCFL, it either died outright instantly, or it caught a case of flicker first. None of that here. This is more like balkiness. Both tubes are still pretty bright, but they just go dark occasionally, or stay dark.

I have never done a tube replacement before myself, but will do one tonight and report back.

Following up... I did replace the CCFL. I had said confidently that I would do it "tonight" on the evening I had posted (since Moniserv is a short drive from where I live).

It took a *lot* longer than one evening. But it is done. See my entry in the CCFL sticky thread for a description of the challenges and risks.