Replacing blown fuse...

[error202]

First post and looking for a little help. I have a T42 that has a blown fuse on the motherboard. I tested with a multimeter and found that F8 is the source of trouble. The blown fuse presents itself as no longer lighting the green leds on the inverter board (battery/hdd activity/power/caps num lock). Only the wifi led is working.

My question to the experienced and knowledgeable: can I use fuses from another source? I have a doner board but it is a Dell Inspiron and have looked it over dozens of times and cannot find a fuse "F" anywhere. I have been helped a lot from other posts describing this fuse and its properties as well as a great fuse map for the T4x series. Could an equivalent fuse be marked as something else? Can I use a fuse close enough in characteristics to get this laptop back in working order? I hope someone else has been in a similar situation and can offer me some advice.

Thanks in advance for any replies!


Mark

[Harryc]

F8 is a 500mA fuse marked 'F', Mouser would be a good source if you are in the US.
http://www.mouser.com/

The problem is going to be to purchase quantity one or two ...

http://www.mouser.com/ProductDetail/Lit ... MWdZaC0%3d

[rkawakami]

And this is where Digikey.com can help sometimes...

http://search.digikey.com/scripts/DkSea ... F2879CT-ND

$US0.97 in single-unit quantities. Shipping is probably going to kill you .

P.S. Welcome to thinkpads.com!

[error202]

rkawakami and HarryC,

Thanks for the quick replies. After looking at the fuse pdf on the T4x series, it mentions a 0603 size and 32V. I was hoping I would be lucky and find something similar on that Dell motherboard that would do the trick. Is it possible to fit the 1206 size wiht 63V on the motherboard?



Mark

[Paul Pennington]

One trick to replacing these surface-mount fuses is to just solder the new one right on top of the old one. The old one is open, and won't interfere with the circuit. Prevents ruining a motherboard trying to get the old fuse out.

Sometimes, the new fuse blows immediately, because the original problem is still there, but it's worth a try before you replace the motherboard.

--Paul

[error202]

Paul,

Thanks for the great tip, I was thinking that it would be next to impossible for me to get that blown fuse off cleanly without damaging something else in the process.


Mark

[error202]

Tonight I have looked over 4 old/spare/junk desktop motherboards, old junk modems, usb 1.1 cards, ethernet cards, a laptop cdrom and other junk video cards...

NOT A SINGLE ONE HAS AN "F" FUSE. WTF??? Did IBM/Lenovo buy up all these little fuses and horde them away? I am amazed that not a single electronic doodad I have around here has an "F" fuse. Wow...



Mark

[rkawakami]

Hmm.. maybe the fuse that Harry and I reference is not the right one. Checking the nice fuse map that's been provided by Nick:

http://nickpaton.fireflyinternet.co.uk/ ... 0Fuses.pdf

F8 is indeed listed as a 0603 size fuse. The 1206 is double the size and probably can't be soldered atop the existing fuse. Looking around, this Littelfuse catalog, http://sigma.octopart.com/10295/datashe ... 34.500.pdf (Slimline 0603 434 series) appears to be the correct one. It's the right size and the "F" marking maps to 0.500A. Digikey has them as "non-stocked" and Mouser currently has a "call to order" note on their page.

edit: Corrected amperage rating of fuse

[error202]

rkawakami,

After some more investigating, I have found a few components that have the blue looking fuse shown in a few of the pics in the fuse pdf. Do you know of anyone or any way to verify if the blue looking fuses are the same thing as the "F" marked fuses?



Mark

[rkawakami]

Not without either a schematic diagram of the board you are getting the fuse off of, or any significant markings that are on the fuse. Littelfuse uses letter codes to denote the amperage rating of the fuse. Another fuse manufacturer could use numbers, symbols, whatever. I don't believe that there's an industry-wide standard for marking fuses (unlike resistor color codes, for example). In situations like this, the recommended procedure is to get an identical (or at least, very similar) motherboard and pull the part off of that one. You just have to hope that the motherboard doesn't have the same problem as yours.

[suzannetf]

Has anyone ever managed to repair this?