T42 voltage regulator question ...

[bmurphy]

I have recently acquired a T42. The AC adapator will not power the laptop or charge the battery.

The AC adaptor is fine, putting out about 16 VDC. The battery will run the laptop fine once it is charged using a external DC supply to charge the battery.

There is no continuity between the pins on the DC power jack. A few possibilities come to mind:

1. Poor solder joints
2. Blown voltage regualtor(s) - I really need a schematic diagram here
3. Reverse polarity diode (if present) blown.

Have anyone on this list repaired a problem of this nature?

Before I tear down the laptop, any tips and/or suggestions would be appreciated. A schematic diagram would be very useful here; if you are willing to share a copy, that would be great. I am willing to attempt a repair on the motherboard myself.

[sjthinkpader]

Welcome to the forum.

Check for blown fuse first. There is a fuse map posted here. Search for it.

[poshgeordie]

The fuses document is here.

Unfortunately there aren't any schematics available.

You say there's no continuity between the pins on the DC Jack - do you mean from the 4 pin connector on the board to the DC Jack? Are you getting 16V measured at the 4 pin connector to the DC jack?

Referring to the fuses diagram check the F2 next to the 4 pin connector - it's the most likely culprit.

FWIW There's also a block diagram a forum member's made of the DC path between DC in and the battery which does show some of the major components: http://dbhome.dk/sma/t41/t41_block_01_v1.1.pdf. While not 100% relevant It may help you a little.

[bmurphy]

Thank you, Nick.

I'll check the F2 fuse first and see what goes.

Regards,
Bernie

The fuses document is here.

Unfortunately there aren't any schematics available.

You say there's no continuity between the pins on the DC Jack - do you mean from the 4 pin connector on the board to the DC Jack? Are you getting 16V measured at the 4 pin connector to the DC jack?

Referring to the fuses diagram check the F2 next to the 4 pin connector - it's the most likely culprit.

FWIW There's also a block diagram a forum member's made of the DC path between DC in and the battery which does show some of the major components: http://dbhome.dk/sma/t41/t41_block_01_v1.1.pdf. While not 100% relevant It may help you a little.

[bmurphy]

Looks like F2 is indeed blown as you suggested. I bridged a fused ammeter across the fuse with the laptop running on battery and the laptop did a beep (I assume that is normal? ) -- also the display got brighter. The ammeter indicated 3.42 amps across the open blown fuse so that is probably OK. Noticed a tiny bit of discolourization on the edge of white mylar sheet which is part of the WiFi module caused by the adjacent surface mount voltage regulator -- hope that the regulator does not have a thermal problem!

My surface mount fixing experiencing is nil. I just need to replace the fuse but things a quite tight in that area of the board. Any suggestions for removing F2? Perhaps cutting the fuse in two with tiny pliers and then lifting it off with solder wick and a small iron? Obviously, a proper SMT air gun is the proper way to do the job but an air gun would cost more than what the T42 laptop is worth

[rkawakami]

A quick-and-dirty method for fixing a blown fuse is to solder the replacement right on top of the old one. The surface mount fuses typically have metal end caps which go all of the way around the ends. Tin the ends on the old fuse and then lay the new one right over it. Apply a small amount of heat on each end and it should adhere just like it was going directly on the motherboard. A soldering iron (of about 25W capability) with the sharpest tip you can get will do the trick.

[bmurphy]

Thank you Ray, for the tip.

Regards,
Bernie

[bmurphy]

The F2 SMT fuse was replaced and the laptop is now fully functional.

Thank you all for your assistance. What a great support group!

Regards,
Bernie

[poshgeordie]

It's a pleasure.