Momentary switch to port replicator power button

hardcoreracing · 02-08-2008, 11:07 AM

I'm trying to use an ibm thinkpad T42 as a carputer. I was planning on connecting a momentary switch to a port replicator so I wouldn't have to hack up my laptop. So after reading another thread about using a multimeter and soldering the contact points around the power button, I gave it a shot.

Problems: Using a multimeter on the port replicator, I wasn't able to get any kind of readings from the contacts around the power button. Am I supposed to have the laptop docked on it to get any kind of readings?

I attempted to solder some of the contacts and now pushing the port replicator power button itself doesn't power on the laptop. Looks like I may have killed it. What other options would I have to turn this laptop on?

FusionFanatic · 02-08-2008, 11:34 AM

1. no, it doesn't need to be docked. in fact it shouldn't be docked.

2. when using a multimeter, you need to press the power button while checking the contacts for continuity (or resistance).

3. you say the switch doesn't work anymore. did you short the contacts by over-soldering? or melt the plastic? assuming it's a mini-tactile switch, does it work by pressing the button itself (not the button cover on the docking station)?

hardcoreracing · 02-08-2008, 12:02 PM

The power button on the port replicator looks a little different than the ones posted on here. It doesn't look like it has any barbs or legs on the top of the power button. The only connection points appear to be on the bottom of the power switch. There are three o the left side connecting the power button to the board. And two on the right side.

#2, I think that could be my problem. I couldn't hold the power button down while I was connecting the two probes to the power button points. How do you guys do this with only two hands?

The difficult part of testing the switch is I have to disassemble the whole port replicator to get to the power button, but to dock the laptop I have to reasseble the whole thing. So when I'm testing the power button it's the button on the docking station cover and not the mini tactile switch itself. I'm really tempted to grab my dremel tool and cut off the power cover so I won't have to keep disassembling the port replicator to get to the power switch.

hardcoreracing · 02-08-2008, 12:59 PM

Looks like I found the thread I need but the pics are gone..

http://www.mp3car.com/vbulletin/powe...elocation.html

hardcoreracing · 02-08-2008, 10:21 PM

Well the docking station is done. The mini tactile button doesn't work anymore as well. I tried soldering the four wires like in the link above but that didn't work too. If anyone has any ideas let me know..

pancit175 · 02-09-2008, 08:07 PM

It may be helpful if you could provide pictures of the docking stations switch

FusionFanatic · 02-11-2008, 10:37 AM

unless you melted the switch or shorted some traces (or left something disconnected) then the switch should be fine.

you don't need to test it with the computer, you only need to test it with a meter. it's easy to do, you can use both hands to position the test leads, then hold both test leads with one hand, use the other to press the tactile button. REMEMBER: the computer should NOT be docked, and no power should be connected when you do this. you're not checking for power output, you're only checking continuity.

if you're sure the switch doesn't work anymore then de-solder it and remove it. once the switch is removed, then remove any leftover solder so you are left with clean solder pads on the circuit board. you can then solder small wires to each trace, which will make it easy to connect a new remote switch. you probably only need two of those wires, but if you're having a hard time testing which ones to use, then it may be easiest to solder all 5 traces and test afterwards. just tape off or cut the wires you don't need.

hardcoreracing · 02-11-2008, 12:08 PM

Thanks for the advice. I guess one of the problems is I'm not very experienced in using a multimeter. Should I be using AC or DC testing voltage? The directions say to start at a high voltage then go lower until there is a reading. Does that sound right? Desoldering the switch seems like an impossibility since I took all the screws out but the circuit board still seems to be glued in the plastic housing so I can't even view the bottom of the circuit board where it is attached to the switch.

I tried soldering all five points, what I did was glop solder bridging the three points on the left to a wire and bridged the two points on the right to another wire. I connected both wires to the momentary switch and still it wouldn't turn on the laptop.

pancit175 · 02-11-2008, 01:36 PM

With the meter you are not going to be testing for any voltage, the unit should not even have any power since its should be unplugged from any power sources. The setting your meter should be in is either continuity or resistance. If you are testing with resistance then it should be at the lowest setting on the meter. While testing 2 contact points and pushing the button, if you get a reading of "0" (zero) or a change in the meter going close to zero (if using continuity some meters will give you an audible beep when continuity is found). Those 2 points will be the points you will solder to.
DO NOT bridge any bits of solder across any contact points, more damage may occur by doing so. There is such a thing as over soldering and under soldering.

FusionFanatic · 02-13-2008, 11:16 PM

first off, you need to remove those "globs" of solder... you should be able to see the traces on the circuitboard.. follow them away from the switch, if they aren't connected on the board then you should not have soldered them together. as pancit mentioned, you can damage the board by doing that.

since you're having a hard time positioning your test leads, then I would suggest you solder an individual wire to each of the five solder points (not globbed together)

now, for your testing. most meters have an audible (beep) continuity tester, it will have a schematic symbol of a speaker and/or diode for that setting. cheap meters often don't have a continuity setting, if yours doesn't then you'll have to use a resistance setting instead (ohm symbol). in either setting, the meter should display zero (or beep) when you touch the leads together. if nothing happens when you touch the leads together then you're in the wrong mode (or you have the leads connected wrong, or the meter is off, or has a dead battery). again, you're not testing power output, so you should NOT be in AC or DC voltage mode.

NOTE: remember to unplug any power cables from the docking station. you don't want to have any power going through it when you're doing this.

hardcoreracing · 02-14-2008, 11:31 AM

Thanks for all your help! I think that was the problem, first thing I was using a cheap soldering iron that had a tip that was too big. It didn't allow me to solder anything without globbing it on. Second mistake was using a cheap multimeter that didn't have the beep option. I was also not testing for continuity or the zero. I was connecting the leads and expecting to see a number appear on the multimeter. My apologies for being a newb. I'll try your suggestions and let you know how it goes. Thanks a bunch!