Screen noise on LCD when connected to AC adapter

[flrthinkpad]

I have a T40p. Last weekend I started seeing streaks across the LCD screen only when it is plugged in to AC power. Symptoms:

1) Does not appear on external monitor.
2) Does not happen when on battery power.
3) Battery is in bad shape. (~2 hours on 9 cell battery.)
4) Observed in window that refreshes. For example video and the emoticons on this page causes the horizontal streaks.
5) Happens when battery is disconnected but on AC power.
6) Observed using three different AC adapters.

Any suggestions? I replaced the power sub- board on a Thinkpad about 5 years. Solder failure led to bad connection.

I just bought a new 100 GB hard drive to upgrade this thing so a shame to dump this machine. Not confident that the new Lenovos have the same quality.

Thanks in advance.

[slagmi]

3 different adapters? Screen brightness and CPU/Bus speed are typically what changes when on AC power. Swap RAM, CPU, else it's the planar.

[flrthinkpad]

Thanks for the reply but I don't agree with the analysis. A quick test of this theory is to turn up the CPU to max on battery -- it has no effect.

Subsequently, I found that squeezing the case to the left of the mouse pad clears up the screen noise.

p.s. I have two IBM OEM adapters and an IGO. In order to check whether the noise is from the AC adapter I hooked it up on all three.

[richk]

It is really hard to diagnose this sort of problem without a circuit diagram. I guess I would look for a blown capacitor near where the A/C jack is, which is very near where the traces go to get to the LCD connector.

[flrthinkpad]

It is really hard to diagnose this sort of problem without a circuit diagram. I guess I would look for a blown capacitor near where the A/C jack is, which is very near where the traces go to get to the LCD connector.

Thanks for the reply.

Would this capacitor be on a "mini-board" for the A/C power? On a clunky Thinkpad from the late 1990s I replaced this board when the A/C jack became loose.

The A/C jack is certainly right next to the strip that goes up to the LCD. Makes sense.

But the squeezing that I described (on the opposite side of the case) suggests a loose connection rather than a bad capacitor, eh?

[slagmi]

Squeezing the case helps= loose component/solder joint, or if you get lucky a bad cable or one that is not well seated. If you're unlucky, it's a cracked planar(scrap).

Search for 'tabook' to find what mini boards are present if any. The 'exploded' diagram found with the lists of service FRU numbers may be the only reference you need.

I don't think that one has a separate i/o board but it's been about 6 months since I've been inside a t4x.

Good luck!

[richk]

The jack is on the main board. There is no mini power board. Squeezing near the touchpad affecting the screen sounds like badly seated graphics chip. One problem is there is no available circuit diagram.