SOLVED: T23 LCD flickers when battery is charging

[RealBlackStuff]

I've got a T23, where the LCD flickers, when the battery is charging.
It's not on/off but it brightes/dims/brightens/dims in a regular pattern.
Replaced LCD, cable and inverter with known good ones, but the problem remains.
All the inductors are properly connected, and without battery it runs perfectly!
What on the motherboard could cause this, maybe a quartz?
Or could it be the I/O board?
Thanks for any hints/solutions.

FYI: there's no flicker on an external monitor, regardless of only external, or external+internal screens on.
The internal one keeps on flickering

[Majestic]

One suggestion.... have you tried another battery pack? Possibly there is a problem with original that is causing a large power drain on the system or the original battery is causing interference.

[RealBlackStuff]

I've tried several (good and bad, all original) batteries, the flicker stays.
It's hardware, because it flickers right away, before any OS loads.
There is no modem or wifi card in it, and no DVD/CD, no ethernet card either.
Swapped RAM to no avail.

[Majestic]

Ok, I suspect you have tried a different AC adapter as well.

[RealBlackStuff]

Yup

[Neil]

I had a T23 a while back that did exactly the same thing. Never did figure out what was causing it. But, it has to be something with the system board.

[jronald]

i have had a couple of T30's do it, when charged with the 56 watt P/S

Ron

[rkawakami]

Before any of you ask or suggest, no, I haven't seen any of my T23s do this . It could be that there's a power drain that is affecting the voltage going to the inverter. If it's a regular pulsing and the system is just sitting at the BIOS display, then I'd suspect the charging circuitry. Since you say that the L7 inductor is firmly attached, put a voltmeter on it when powering up and see if you can detect any voltage change that occurs in sync with the flickering.

Another thing comes to mind... check the BIOS setting for the display brightness (Config/Display/Brightness). If it is set to Normal, change it to High and see if that makes any difference.

edit: Found some related threads in the archives:

http://forum.thinkpads.com/viewtopic.php?f=28&t=53091 (T20 flickers when charging battery - no published solution)
http://forum.thinkpads.com/viewtopic.php?f=28&t=52961 (T23 flickers when charging battery - no published solution)

[RealBlackStuff]

That was a sneaky one!
Even with plenty of manual force, the L7 inductor (~1" left and up of the battery contacts) would not come off.
So I put some pressure on it, just for the heck of it, and by doing so I must have re-established enough contact, because the flickering stopped!
When I then used a soldering iron, it came off very quickly, showing plenty of corrosion!
Cleaned that up and resoldered it, now the patient has a clean bill of health again.
Thanks Ray, for still doubting the L7 inductor.