T42 LCD switch broke. Need to bypass.

[jparkerri]

I have a T42 14.1" and the screen kept blinking out. I replaced the inverter board and it still did it. I tested the old inverter board in another T42 and it worked fine so I went looking at the switch that's pushed when you close the lid. By pushing it quickly I could get the screen to come on momentarily. When I got to the actual switch, one of the three solder points was broken. I took it all the way off and tried to solder a bypass to keep the screen on but was not successful. Has anyone ever bypassed this switch to keep the screen on? BTW, the computer works fine with an external monitor but I'd prefer the laptop screen. This switch is part of the ribbon cable going up behind the screen. If I get a whole new screen, I assume I'll get a new switch on the cable, right?

Any help or suggestions appreciated.

[jdhurst]

That switch is the suspend switch, so probably something else is causing the screen to blink. Yes, if you replace the lid, the switch comes with it. Replacing the lid is probably the best way to deal with screen problems (at least in my own experience). ... JDH

[virge]

When I got to the actual switch, one of the three solder points was broken. I took it all the way off and tried to solder a bypass to keep the screen on but was not successful. Has anyone ever bypassed this switch to keep the screen on?

You know, it's just a guess, but it sounds like you have a backlight/LCD problem. I've never played around with that switch before, but it seems to me that if the switch is removed, then the screen should never go off even if the lid is closed. Completely a guess of course.

Since you seem to know what you're doing (I took a look at the switch on one of my cables and there is NO way I could resolder it!), check out these links:

http://forum.thinkpads.com/viewtopic.php?t=47235
http://www.rkawakami.net/ibm_600x/sub_card/

Its not the same machine, but the technical description of how the switch works may be similar... and its written by one of the very knowledgeable mods here.

[richk]

You can replace the cable or the entire assembly. If you want to discuss an exchange, send me a PM

[rkawakami]

Looking at one of my detached T41 lid assemblies, the microswitch appears to be what's called a "normally open" switch. This means that if nothing is done to disturb it (i.e., the button is not pressed down), then there is an open circuit between the switch contact points. Since there's three terminals, there are six different combinations to test for. Putting an ohmmeter across the terminals and pushing the button yields this:

http://www.kawakami-ca.com/images/t41_ribbon_cable1.jpg
http://www.kawakami-ca.com/images/t41_ribbon_cable2.jpg
http://www.kawakami-ca.com/images/t41_ribbon_cable3.jpg

So therefore, if you wish to bypass the switch and have it never blank out the backlight, you can simply remove the entire switch assembly and short the two pins on the "right" side (as viewed in my photos).

Note: This is all theoretical information based upon the measurements I made. Obviously the safest thing you can do is replace the entire ribbon cable with a compatible model for your system. That would allow you to put the system into standby or hibernation by simply closing the lid. The other option, if there's no damage to the circuit board, is to locate a replacement switch. Mouser or DigiKey probably carries them. It just takes a little searching around for the right part.

edit: This looks like the right one:

http://se.mouser.com/Search/Refine.aspx ... s=P_SField (search for SPVE110600 at mouser.com)
http://www3.alps.com/WebObjects/catalog ... E/SPVE.PDF (ALPS datasheet)

edit2: Duh! I forgot to measure the height of the switch.; there's three different versions. I'll update this post when I get home tonight. Yup, it's the 3.8mm height version.