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T42 blown Fuse *PIC*

T4x series specific matters only
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moerph
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T42 blown Fuse *PIC*

#1 Post by moerph » Mon Jan 14, 2008 3:31 am

Hello,

I´ve got a T42 with a blow Fuse right behind the DC Jack labeled F2. Since there ist a marking on top stating "FU". I´ve got no idea what that mean. The F i think means that is a fast Type but i found nothing about the "U". It should state the Ampere Rating but i dont know which. Does anyone know the correct values of this fuse ?

thank you
moerph

Moderator note: Added PIC in subject line per request

sojourner
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#2 Post by sojourner » Mon Jan 14, 2008 9:09 am

I don't know what the markings mean (Canadian UL approval?) and wonder if that component is really a fuse (never had one apart that far to be familiar with it)! Did you check across the leads with a continuity tester? Are you are sure there is a complete break (blown 'fuse')?

If you are sure the component is a blown fuse you could try the following. Being I have never seen the battery charge rate indicator above 35 watts (and I take my batteries down to 10v, that's .1 to .2v just before the TP dies from low voltage, so the charge rate is maxed out), and assuming the TP itself draws a max of 20 watts (though I've never seen it that high), the fuse needs to handle 35 + 20 = (approx.) 55 watts / 16v = 3.44 amps minimum (approx.).

One last thought; the charger for my T41 allows up to 4.5 amps 16v draw (72 watts) ... but I don't think you'd ever see your lappie draw that much unless something was wrong. A common Raychem fast acting SMD chip fuse, 4 amps 24v (0402 series, .39 cents US) should work.

Personally however, I'd look into WHY the fuse blew before doing anything. Then, perhaps take a cheap common fast blow 1.5 - 2 amp fuse, attach it, and with battery removed try starting TP. If a 2 amp blows under those condition I'd be inclined to think there is a serious problem on the mobo or with one of the perpherials.
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#3 Post by Robbyrobot » Mon Jan 14, 2008 9:42 am

I don't know what the markings mean (Canadian UL approval?) and wonder if that component is really a fuse
For what it's worth, I first answered moerph in the German Thinkpad forum and suggested he ask here. I think the fuse he refers to is this one:
Image
As you see, it's right to the left of the mainboard power socket, and it would be logical for it to blow if an incorrect AC power suppy had been attached. The other question is whether anything else is damaged, and that will only become apparent after the fuse is replaced or provisionally bridged to see if the computer runs at all.

P.S. Could moerph or a moderator change the subject to reflect an image here? I can't do that myself.

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#4 Post by moerph » Mon Jan 14, 2008 11:54 am

Hello,


after hours of searching i found out what the marking on the Fuse means.

The marking "FU" on this Fuse means that it is a fast acting fuse rated at 7 amps.

thanks
moerph

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#5 Post by Robbyrobot » Mon Jan 14, 2008 12:54 pm

SEVEN Amps :roll: ?? I'm no electronics expert, but that seems just a bit high to me.

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#6 Post by sojourner » Mon Jan 14, 2008 1:12 pm

Robbyrobot wrote:SEVEN Amps :roll: ?? I'm no electronics expert, but that seems just a bit high to me.
I believe you are right! I too am not an EXPERT but a hobbiest. But to the best of my knowledge I have NEVER heard of a fuse amperage rating being LARGER than what the supply could provide !!!

In other words, does it make sense to have a supply of 4.5 amps and a 7 amps fuse to protect the laptop?

Your home likely has a supply source which can provide HUNDREDS of amps (e.g. 500 amps from tramsformer), however the house likely has a MAIN curcuit breaker (fuse) of two hundred amps (USA), which is less than the supply source, which is the way it always should be!

I did a little more research; with the little I know and can see from the excellent picture, that fuse is likely (or similar too) Raychem's fast acting SMD chip fuse series 1206, 4 amp 32v (dim's mm 1.1 x 1.6 x 3.2 [inch .043 x .063 x .126]). If your TP has the 90 watt supply you could use a five amp chip fuse. They made this chip up to 8 amps in this envelope size.

PDF: http://www.mouser.com/catalog/632/500.pdf
IBM Thinkpad T41 Home | X31 Travel | X60 fun
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#7 Post by rkawakami » Mon Jan 14, 2008 2:08 pm

The main fuse I've found on T23 motherboards are also labeled FU and are 7A fuses made by Littelfuse and can be found at mouser.com. The one you have in the T41 looks the same. Check this image:

http://www.rkawakami.net/ibm_t2x/let.jpg

At the top of the picture, next to the designation "F2", you should see the same type of fuse.
Ray Kawakami
X22 X24 X31 X41 X41T X60 X60s X61 X61s X200 X200s X300 X301 Z60m Z61t Z61p 560 560Z 600 600E 600X T21 T22 T23 T41 T60p T410 T420 T520 W500 W520 R50 A21p A22p A31 A31p
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#8 Post by SteveS » Mon Jan 14, 2008 9:10 pm

sojourner wrote:
I believe you are right! I too am not an EXPERT but a hobbiest. But to the best of my knowledge I have NEVER heard of a fuse amperage rating being LARGER than what the supply could provide !!!

In other words, does it make sense to have a supply of 4.5 amps and a 7 amps fuse to protect the laptop?
I have designed electronic equipment and can tell you that it is common practice to design in a fuse of higher rating that either the supply rating or load are expected to draw. The fuse is not intended to protect the power supply – it has built in current limiting. 7A is probably reasonable for the main power circuit in a T40 series. The fuse should blow only in an extreme fault condition – one in which the current is high enough to destroy other components or cause a fire from overheating circuit board traces. The inrush current during power on is quite high as all the capacitors are discharged. This stresses the fuse, and would eventually open one that was just rated at the current needed for the circuit.

BTW, the 4.5 A is needed for the PC, charging the battery, and powering 3 USB ports at ½ A each (2 on the PC and one on the port replicator.) I ran across a note on the IBM web site some time ago that indicated operating a T40 series on a 56W supply may result in unstable operation when using all of the USB ports.

Another interesting point – I have counted 17 fuses on the T43 system board! There may be more, but that is all I found.
2668G1U

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#9 Post by richk » Mon Jan 14, 2008 10:46 pm

The ones that are in the supply circuit from the batteries are 10 amp and I have seen them blown. (One can only imagine how) When I get boards that won't charge a battery or draw from a battery or won't take A/C, I always check the fuses. I have also tried countring the fuses, but I tend to lose interest. Many are stuck under the black covers. When I find them blown, I just pull one off a junk board in the same location.

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#10 Post by Robbyrobot » Tue Jan 15, 2008 2:09 am

The main fuse I've found on T23 motherboards are also labeled FU and are 7A fuses...
Amazing... learned something today :)

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#11 Post by rkawakami » Tue Jan 15, 2008 3:17 am

Here's another.... as I said in the post that I originally posted that picture in, semiconductor circuits protected by a fast-acting fuse with self-destruct FIRST, thereby protecting the fuse :) . Learned that Murphy's Law many, many years ago with transistorized circuits and it still remains true even with today's ICs.
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X22 X24 X31 X41 X41T X60 X60s X61 X61s X200 X200s X300 X301 Z60m Z61t Z61p 560 560Z 600 600E 600X T21 T22 T23 T41 T60p T410 T420 T520 W500 W520 R50 A21p A22p A31 A31p
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#12 Post by billymm » Mon Apr 21, 2008 8:02 pm

Hi all,

I was just wondering does anyone know what those 3 green things are in the bottom left of the pic that Robbyrobot kindly supplied?

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#13 Post by sjthinkpader » Tue Apr 22, 2008 12:44 am

They look like resistors.

As for the fuse, when voltage goes lower, the amperage goes higher to arrive at the same power. This is frequently the problem with low voltage semiconductor. 7 amp at 3 volts is only 21 watts.

The AC adapter is rated lower in amperage but higher in voltage.

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#14 Post by rkawakami » Tue Apr 22, 2008 1:20 am

sjthinkpader wrote:They look like resistors.
Although they don't look like a regular ceramic chip resistor, that seems to be a very good evaluation based upon this: Here's a photo that I've posted before showing the area near the DC input jack on a T23 motherboard:

http://www.rkawakami.net/ibm_t2x/let.jpg

You can see the same 7A F2 "FU" fuse near the top edge of the picture. Right below it is Q33, a MOSFET I believe, three of those same green resistors (labeled R225, 226 and 227) between it and another MOSFET, Q5. However, if I measure the resistance across those three resistors, I read very close to a dead short (0 ohms). If they are resistors, they have to be less than 1 ohm each since the three in parallel would be 1/3 the value of a single one (assuming they are of the same value). In this case, I'd be tempted to call them "fuses" as well :) .
Ray Kawakami
X22 X24 X31 X41 X41T X60 X60s X61 X61s X200 X200s X300 X301 Z60m Z61t Z61p 560 560Z 600 600E 600X T21 T22 T23 T41 T60p T410 T420 T520 W500 W520 R50 A21p A22p A31 A31p
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Re:

#15 Post by misfit » Thu Sep 15, 2011 2:25 am

sojourner wrote:I did a little more research; with the little I know and can see from the excellent picture, that fuse is likely (or similar too) Raychem's fast acting SMD chip fuse series 1206, 4 amp 32v (dim's mm 1.1 x 1.6 x 3.2 [inch .043 x .063 x .126]). If your TP has the 90 watt supply you could use a five amp chip fuse. They made this chip up to 8 amps in this envelope size.

PDF: http://www.mouser.com/catalog/632/500.pdf
Well, I currently have this problem with an R52, fuse F2 is open-circuit. I'm not that clued-up about electronics but have fixed this issue before with a T43p, removing F2 from a T43 that had a loose southbridge and piggy-backing it onto the blown fuse and it worked (and continues to work) perfectly.

However, this time I don't have a donor machine so decided to go to a site that I've used in the past for components. [http://www.activecomponents.com/Page-Products_0.aspx] They've been good both times I've used them before, displaying in NZ$ and delivering within a week or so after the components were ordered and paid for.

However, this time, trying to place an order has me tearing my hair out. The problem is I don't really speak electronics but have managed to fumble my way through in the past. This time I've had no luck finding a fuse suitable. I simply don't know how to set the search parameters and have had to give up trying thrice now due to excessive anxiety and lack of results. I'm afraid that, if I try again I'm likely to lose what's left of my mind.

If any kind member would care to look there and tell me the part number of a suitable component I would be deeply, deeply indebted. I wouldn't ask if I hadn't hit a brick wall....

Any help most gratefully accepted.
Shaun.
T60 2007-72U [T7400, UXGA FV]
T43p 2668-H2M [FV]
T43 2668-84M [FV]
R52 1847-A18
T42p 2373-KXM [FV]
T42 2374-M97 [SXGA+]
R51 1829-E5C [FV]
R40 2723-BAM [SXGA+]
R40 2723-26M
X32 x 2 2672-CM5/W58
X31's x 8 Four working.
X30 2672-4HM
X24 2662-FMT
Etc.

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Re: T42 blown Fuse *PIC*

#16 Post by RealBlackStuff » Thu Sep 15, 2011 6:04 am

This will be your life-saver: http://theboardroom.info/T4x_Fuses.pdf
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Re: T42 blown Fuse *PIC*

#17 Post by misfit » Thu Sep 15, 2011 6:40 am

RealBlackStuff wrote:This will be your life-saver: http://theboardroom.info/T4x_Fuses.pdf
Gosh darn it! I downloaded that ages ago but didn't realise that it had part numbers as I was more looking at the fuse locations!

Thanks heaps Dom (and Nick), I've just ordered 15 of the little things (and a flux pen, minimum order of $20) so, going by past experience I'll have them in a couple of weeks or so.

Thanks again. I can't believe I didn't notice that myself! My next step was to consult that pdf and look to see if there was another fuse on the donor T43 that I could substitute for F2.

:bow: :bow: :bow:
Shaun.
T60 2007-72U [T7400, UXGA FV]
T43p 2668-H2M [FV]
T43 2668-84M [FV]
R52 1847-A18
T42p 2373-KXM [FV]
T42 2374-M97 [SXGA+]
R51 1829-E5C [FV]
R40 2723-BAM [SXGA+]
R40 2723-26M
X32 x 2 2672-CM5/W58
X31's x 8 Four working.
X30 2672-4HM
X24 2662-FMT
Etc.

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